Assessment of Environmental Impact of STP Discharge to Evans River

A part of BMT in Energy and EnvironmentAssessment of Environmental Impactof STP Discharge to Evans RiverFinal ReportSeptember 2010

DOCUMENT CONTROL SHEETBMT WBM Pty LtdBMT WBM Pty LtdLevel 11, 490 Upper Edward StreetBrisbane 4000Queensland AustraliaPO Box 203 Spring Hill 4004Tel: +61 7 3831 6744Fax: + 61 7 3832 3627ABN 54 010 830 421www.wbmpl.com.auDocument :Project Manager :Client :Client Contact:R.B17607.001.03.Revised Final.docDamion CavanaghRichmond Valley CouncilMark HesseClient Reference166.09Title :Author :Synopsis :Assessment of Environmental Impact of STP Discharges to the Evans River – FinalReportDamion Cavanagh; Fanny Houdré; Dr Michael Barry; Ryan Shojinaga; Rylan Loemkerand Ben AsquithThis report provides an assessment of the risk of impact from a number of dischargescenarios from the Evans Head Sewage Treatment Plant (STP) to the Evans River.The report initially provides a review of key estuarine processes governing waterquality within the estuary. The report then outlines various field data collectionactivities that have been undertaken for the purposes of establishing calibrated andvalidated hydrodynamic and advection-dispersion models of the Evans River. Finally,scenarios are assessed which examine the potential social and environmental impactsof ebb-tide, continuous and wetland / forest discharge options.REVISION/CHECKING HISTORYREVISIONDATE OF ISSUE CHECKED BY ISSUED BYNUMBER0 22 June 2010 M. Barry D. Cavanagh1 13 July 2010 M. Barry D. Cavanagh2 26 August 2010 M. Barry D. Cavanagh3 16 September 2010 M. Barry D. CavanaghDISTRIBUTIONDESTINATIONRichmond Valley CouncilBMT WBM FileBMT WBM LibraryREVISION0 1 2 32 + PDF2PDFPDFPDFPDF4 + PDFPDFPDF4 + PDFPDFPDFG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CONTENTSICONTENTSContentsList of FiguresList of TablesGlossaryExecutive Summaryivixxixiii1 INTRODUCTION 1-11.1 Background 1-31.2 Location and Overview of the Evans River 1-41.2.1 Rainfall and Climate 1-62 DATA COLLECTION AND REVIEW 2-12.1 Field Data 2-12.1.1 Tidal Flow 2-12.1.2 Conductivity, Temperature, Depth (CTD) and Turbidity 2-52.2 Existing Reports 2-82.3 MHL Data 2-92.3.1 Estuary Tide Heights 2-92.3.1.1 Fixed Recorders 2-92.3.1.2 Temporary Recorders 2-102.3.2 Tidal Velocity and Flow 2-132.3.3 Ocean Tide Heights 2-132.4 BoM Data 2-152.5 Bathymetric Data 2-162.6 Water Quality Data 2-202.6.1 Beachwatch Data 2-202.6.2 Council and DECCW Data 2-212.6.2.1 Water Quality Guidelines and Environmental Values 2-222.6.2.2 Comparison of Recorded Water Quality against Guideline TriggerValues 2-242.6.2.3 Key Points 2-302.7 Sewage Treatment Plant Flow and Quality 2-313 REVIEW OF ESTUARY PROCESSES 3-1G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CONTENTSII3.1 Entrance Conditions 3-13.2 Catchment Inputs 3-33.2.1 Internal Inputs 3-33.2.2 External Inputs 3-53.3 Sediments 3-103.4 Estuarine Hydrodynamics 3-103.4.1 Tidal Planes 3-113.4.2 Tidal Lags 3-133.4.3 Tidal Phasing 3-143.4.4 Tidal Flushing 3-163.4.5 Tidal Excursion 3-163.5 Water Quality 3-173.5.1 Dry Weather 3-173.5.2 Catchment Rainfall Events (No Overtopping of Tuckombil Weir) 3-193.5.3 Catchment Rainfall Events (Plus Overtopping of Tuckombil Weir) 3-203.6 Ecosystem Characteristics 3-203.7 Potential Ecosystem Responses 3-243.8 Social and Environmental Values 3-243.9 Summary of Processes 3-294 CATCHMENT MODELLING 4-14.1 WaterCAST Catchment Modelling Framework 4-14.1.1 Data Requirements for a WaterCAST Model 4-14.2 Evans River WaterCAST Input Data 4-24.2.1 Subcatchment Map 4-24.2.2 Land Use 4-44.2.3 Rainfall and Evapo-transpiration 4-74.2.4 Hydrology 4-74.2.5 Water Storages and Point Sources 4-84.3 Model Results 4-84.3.1 Estimated Total and Mean Annual Flows 4-94.3.2 Estimated Mean Annual Land Use Flows 4-104.3.3 Temporal Representation 4-104.3.4 Results Summary 4-115 WETLAND AND CARBON SEQUESTRATION MODELLING 5-15.1 Peer Review of Water and Carbon Group Models 5-15.1.1 Free Water Surface Wetland Treatment Performance 5-1G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CONTENTSIII5.1.2 Wetland Carbon Forest and Wetland Hydrology 5-25.2 Preliminary Concept for Modelling 5-45.3 Methodology and Data Input 5-45.3.1 Models Used 5-55.3.1.1 Reed Free Water Surface Wetland Model 5-55.3.1.2 MEDLI 5-55.3.1.3 Decentralised Sewage Model (DSM) 5-65.3.2 Development of Indicative Site Characteristics 5-75.3.2.1 Soil and Groundwater Dynamics 5-95.3.3 Free Surface Water Wetland Treatment Performance 5-105.3.3.1 Inflows from Evans Head STP 5-105.3.3.2 Wetland Configuration 5-115.3.3.3 Rate Constants and Temperature Coefficients 5-115.3.3.4 Background Concentrations 5-125.3.4 Hydrology and Nutrient Processes 5-125.3.4.1 STP Inflow and Concentration 5-135.3.4.2 Climate 5-135.3.4.3 System dimensions and configuration 5-145.3.4.4 Soil and Landscape Characteristics 5-155.3.4.5 Plant (Forest) Parameters 5-185.3.4.6 Irrigation Infrastructure and Scheduling 5-205.3.4.7 MEDLI Model Runs 5-215.3.5 Pathogens 5-215.3.6 Time Series for Modelling 5-225.4 Results 5-235.5 Outcomes and Recommendations 5-266 HYDRODYNAMIC MODELLING 6-16.1 Approach 6-16.2 Selection of Modelling Periods 6-16.3 Model Development 6-16.3.1 Model Extent and Mesh Definition 6-16.3.2 Bathymetry 6-36.3.3 Tidal Boundary Conditions 6-56.3.4 Meteorological Wind Forcing 6-66.3.5 Material Properties 6-66.3.6 Advection Dispersion Parameterisation 6-86.4 Model Calibration and Validation 6-86.4.1 Hydrodynamic Calibration 6-8G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CONTENTSIV6.4.1.1 Calibration Data 6-86.4.1.2 Calibration Results – Water Levels 6-86.4.1.3 Calibration Results – Flows 6-126.4.1.4 Discussion 6-136.4.2 Hydrodynamic Validation 6-146.4.2.1 Validation Data 6-146.4.2.2 Validation Results – Water Levels 6-146.4.2.3 Discussion 6-216.4.3 Model Continuity 6-216.4.4 Advection Dispersion Calibration 6-246.4.4.1 Calibration Data 6-246.4.4.2 Calibration Results – Salt Recovery 6-256.4.4.3 Discussion 6-276.4.5 Assumptions and Limitations 6-287 STP DISCHARGE SCENARIOS 7-17.1 Discharge Alternatives 7-17.1.1 Continuous and Ebb Discharge 7-17.1.2 Wetland / Forest Discharge 7-47.2 Modelling Period 7-57.3 Modelled Constituents 7-57.4 Modelling Framework 7-67.4.1 CORMIX Modelling 7-67.4.1.1 Inputs 7-67.4.1.2 Diffuser Configuration 7-77.4.2 RMA Modelling – Combination Method 7-87.5 Results 7-97.5.1 CORMIX 7-97.5.2 Advection-Dispersion Model 7-97.5.2.1 Data Extraction Locations 7-97.5.2.2 Continuous and Ebb-Tide Results 7-117.5.2.3 Effect of Reduced Discharge Periods for Ebb-Tide Discharges 7-237.5.2.4 Wetland / Forest Results 7-287.6 Summary of Findings 7-378 DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-18.1 Water Quality 8-18.1.1 Continuous and Ebb-tide Release Options 8-28.1.2 Wetland / Forest Release Options 8-3G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

LIST OF FIGURESV8.2 Physical Constraints Impacting on Discharge Constructability 8-48.2.1 Floods 8-58.2.2 Commercial and/or Recreational Interaction 8-108.2.3 Wave Conditions and Sand Movement 8-138.3 Operational Considerations 8-158.4 Construction Considerations 8-168.4.1 Terrestrial Pipeline from STP 8-168.4.2 Marine Pipeline and Discharge Structure 8-178.5 Potential Ecosystem Responses 8-188.6 Social and Environmental Value Impacts 8-198.7 Discharge Scenario Impact Risk Assessment 8-208.8 Approval Considerations 8-279 CONCLUSIONS AND RECOMMENDATIONS 9-19.1 Conclusions 9-19.2 Recommendations 9-49.3 Further Assessments 9-510 REFERENCES 10-1APPENDIX A: EVANS RIVER REVIEW OF ENVIRONMENTAL VALUESAND WATER QUALITY OBJECTIVES (HYDROSPHERE,2009) A-1APPENDIX B: ANALYSIS OF EVANS HEAD STP FLOWS INTERIMREPORT (HYDROSPHERE, 2010) B-1APPENDIX C: CREATING A WATERCAST CATCHMENT MODEL C-1APPENDIX D: WATERCAST WATER QUALITY ASSESSMENTS D-1LIST OF FIGURESFigure 1-1 Evans River Locality Map 1-5Figure 1-2 Rainfall, Wind and Temperature Data for Evans Head (VaryingPeriods) 1-6Figure 2-1 CTD Recorder and ADCP Transect Locations 2-2Figure 2-2 ADCP and GPS Instrumentation aboard Vessel 2-3Figure 2-3 Downstream Transect – Spring Tide (2 February 2010) 2-3G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

LIST OF FIGURESVIFigure 2-4 Upstream Transect – Spring Tide (3 February 2010) 2-4Figure 2-5 Downstream Transect – Neap Tide (8 February 2010) 2-4Figure 2-6 CTD Instrument and Turbidity Meter on Bottom Mount 2-5Figure 2-7 CTD Record – Initial Upstream Location (Upstream 1) 2-6Figure 2-8 CTD Record – Final Upstream Location (Upstream 2) 2-7Figure 2-9 CTD Record – Downstream Location (Downstream) 2-8Figure 2-10 Tidal Levels – Evans River Iron Gates and Fishing Co-op Sites 2-10Figure 2-11 Tidal Levels – Evans River Temporary Sites 2-11Figure 2-12 MHL Temporary and Permanent Tide Recorders 2-12Figure 2-13 Evans River Entrance Transect (Site 3) – 2 March 2006 2-13Figure 2-14 MHL Ocean Tide Recorders and BoM Evan Head RAAF AWS 2-14Figure 2-15 Ocean Level Data 2-15Figure 2-16 Evans Head RAAF Weather Station Data Sample 2-16Figure 2-17 Evans River and Ocean Digital Elevation Model (Downstream) 2-18Figure 2-18 Evans River and Ocean Digital Elevation Model (Upstream) 2-19Figure 2-19 Map of Council and DECCW Sample Sites (Hydrosphere, 2009) 2-22Figure 2-20 Council Water Quality Data (38 samples per site) 2-25Figure 2-21 DECCW Nitrogen Water Quality Data (6 samples per site) 2-29Figure 2-22 DECCW Phosphorus Water Quality Data (6 samples per site) 2-29Figure 2-23DECCW Electrical Conductivity and Chlorophyll-a Water QualityData (13 samples per site) 2-30Figure 3-1 Schematic of Estuarine Process Interactions 3-1Figure 3-2 Aerial Photographs of Lower Estuary 3-3Figure 3-3 Tuckombil Weir 3-5Figure 3-4 Rocky Mouth Creek Pacific Highway Bridge Tide Recorder 3-7Figure 3-5 June 2005 Flooding Event 3-8Figure 3-6 Comparison of tide heights over December 2007 to June 2008 3-9Figure 3-7 Locations of Tide Recording (MHL, 2006) 3-11Figure 3-8 Tidal Planes for Data Collected 7/12/05 to 19/01/06 (MHL, 2006) 3-12Figure 3-9Comparison of Recorded Tide Heights and Discharge at Sites‘Entrance’ and ‘Upstream 1’ 3-15Figure 3-10 Conductivity Time Series, August 2006 to February 2009(Source Council) 3-18Figure 3-11 TN Time Series, August 2006 to February 2009 (Source Council) 3-18Figure 3-12 TP Time Series, August 2006 to February 2009 (Source Council) 3-20Figure 3-13 Seagrasses, Mangroves and Saltmarsh Distribution Evans River 3-22Figure 3-14 Minor fish kill at Tuckombil Weir (March, 2010) 3-23Figure 4-1 Evans River Subcatchment Map 4-3Figure 4-2 Evans River Land Use Map 4-6Figure 4-3 Tuckombil Canal Inflow Time Series 4-8Figure 4-4 Evans River WaterCAST Model 4-9G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

LIST OF FIGURESVIIFigure 4-5 Estimated Annual Flows 4-11Figure 5-1Figure 5-2Indicative Wetland / forest Effluent Management Concept used forModelling 5-5Structure of MEDLI (Source: MEDLI Technical Description,Queensland DNR) 5-6Figure 5-3 Summary of the Structure of the DSM 5-7Figure 5-4Figure 5-5Indicative Discharge Locations for Wetland / forest EffluentManagement Systems 5-8Comparison of WCG MEDLI STP Inputs and Values Adopted forthis Study 5-13Figure 5-6 MEDLI Pond Input Parameters 5-14Figure 5-7 Soil Landscapes and Profiles used in Forest Modelling 5-16Figure 5-8 MEDLI Plant Parameters 5-19Figure 5-9 Biomass Accumulation (Standing Yield) for the Wetland Forest 5-19Figure 5-10 MEDLI Irrigation Parameters 5-20Figure 5-11 Water Balance for Selected Wetland / Forest Sites 5-24Figure 5-12 Net Changes in Water Balance for Selected Wetland / Forest Sites 5-25Figure 5-13Net Changes in Total Nutrients Loads for SelectedWetland / Forest Sites 5-25Figure 6-1 Evans River RMA Model Mesh 6-2Figure 6-2 Evans River RMA Model Bathymetry 6-4Figure 6-3 HD Calibration Tidal Boundary 6-5Figure 6-4 HD Validation Tidal Boundary 6-5Figure 6-5 AD Calibration Tidal Boundary 6-6Figure 6-6 Evans River RMA Model Material Distribution 6-7Figure 6-7 HD Calibration – Water Levels – Upstream 1 6-9Figure 6-8 HD Calibration – Water Levels – Upstream 1 – Zoom 6-9Figure 6-9 HD Calibration – Water Levels – Upstream 2 6-10Figure 6-10 HD Calibration – Water Levels – Upstream 2 – Zoom 6-10Figure 6-11 HD Calibration – Water Levels – Downstream 6-11Figure 6-12 HD Calibration – Water Levels – Downstream – Zoom 1 6-11Figure 6-13 HD Calibration – Water Levels – Downstream – Zoom 2 6-12Figure 6-14 HD Calibration – Spring Tide Flows – Upstream Section 6-12Figure 6-15 HD Calibration – Spring Tide Flows – Downstream Section 6-13Figure 6-16 HD Calibration – Neap Tide Flows – Downstream Section 6-13Figure 6-17 HD Validation – Water Levels – Site 11 – December 2005 6-15Figure 6-18 HD Validation – Water Levels – Site 9 – December 2005 6-15Figure 6-19 HD Validation – Water Levels – Site 7 – December 2005 6-16Figure 6-20 HD Validation – Water Levels – Iron Gate – December 2005 6-16Figure 6-21 HD Validation – Water Levels – Site 5 – December 2005 6-17Figure 6-22 HD Validation – Water Levels – Fishing Coop – December 2005 6-17Figure 6-23 HD Validation – Water Levels – Site 2 – December 2005 6-18G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

LIST OF FIGURESVIIIFigure 6-24 HD Validation – Water Levels – Site 11 – January 2006 6-18Figure 6-25 HD Validation – Water Levels – Site 9 – January 2006 6-19Figure 6-26 HD Validation – Water Levels – Iron Gate – January 2006 6-19Figure 6-27 HD Validation – Water Levels – Site 5 – January 2006 6-20Figure 6-28 HD Validation – Water Levels – Fishing Coop – January 2006 6-20Figure 6-29 HD Validation – Water Levels – Site 2 – January 2006 6-21Figure 6-30 Evans River RMA Model Continuity Check Sections 6-23Figure 6-31 AD Calibration – Salinity – Council Site 1 6-25Figure 6-32 AD Calibration – Salinity – Council Site 2 6-26Figure 6-33 AD Calibration – Salinity – Council Site 3 6-26Figure 6-34 AD Calibration – Salinity – Council Site 4 6-27Figure 6-35 AD Calibration – Salinity – Council Site 5 6-27Figure 7-1 Continuous and Ebb-Tide Discharge Locations 7-2Figure 7-2 Effluent Flow Rates (2008) 7-3Figure 7-3 Weekly Effluent Water Quality (2008) 7-3Figure 7-4 Tuckombil Canal Wetland / Forest Discharge Flows (2008) 7-4Figure 7-5 Brandy Arm Creek Wetland / forest Discharge Flows (2008) 7-5Figure 7-6 Model Data Extraction Locations 7-10Figure 7-7Continuous and Ebb-Tide Discharge, Point 2 (Tuckombil Canal),Total Nitrogen (2008) 7-11Figure 7-8 Continuous and Ebb-Tide Discharge, Point 4, Total Nitrogen (2008) 7-12Figure 7-9 Continuous and Ebb-Tide Discharge, Point 5, Total Nitrogen (2008) 7-12Figure 7-10 Continuous and Ebb-Tide Discharge, Point 6, Total Nitrogen (2008) 7-13Figure 7-11 Continuous and Ebb-Tide Discharge, Point 7, Total Nitrogen (2008) 7-13Figure 7-12Figure 7-13Figure 7-14Figure 7-15Figure 7-16Figure 7-17Figure 7-18Figure 7-19Figure 7-20Continuous and Ebb-Tide Discharge, Point 8 (Entrance),Total Nitrogen (2008) 7-14Continuous and Ebb-tide Discharge, Beach Point, TotalNitrogen (2008) 7-14Continuous and Ebb-Tide Discharge, Point 2 (Tuckombil Canal),Total Phosphorus (2008) 7-15Continuous and Ebb-Tide Discharge, Point 4, Total Phosphorus(2008) 7-15Continuous and Ebb-Tide Discharge, Point 5, Total Phosphorus(2008) 7-16Continuous and Ebb-Tide Discharge, Point 6, Total Phosphorus(2008) 7-16Continuous and Ebb-Tide Discharge, Point 7, Total Phosphorus(2008) 7-17Continuous and Ebb-Tide Discharge, Point 8 (Entrance), TotalPhosphorus (2008) 7-17Continuous and Ebb-tide Discharge, Beach Point, TotalPhosphorus (2008) 7-18G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

LIST OF TABLESIXFigure 7-21Incremental TN Concentrations Resulting from ContinuousRelease at Entrance - Neap Tide 27 July 2008 (left), SpringTide 3 August 2008 (right) 7-19Figure 7-22 Total Nitrogen, Continuous Discharge Impacts 7-24Figure 7-23 Total Nitrogen, Distribution of Ebb-tide Discharge Impacts 7-25Figure 7-24 Total Phosphorus, Distribution of Continuous Discharge Impacts 7-26Figure 7-25 Total Phosphorus, Distribution of Ebb-tide Discharge Impacts 7-27Figure 7-26 Net Wetland / Forest Runoff for Selected Schemes 7-28Figure 7-27Figure 7-28Comparison of Upper Catchment Flows to Net Wetland / ForestRunoff 7-29Wetland / Forest Discharge, Point 1 (Upstream), Total Nitrogen(2008) 7-31Figure 7-29 Wetland / Forest Discharge, Point 2, Total Nitrogen (2008) 7-31Figure 7-30 Wetland / Forest Discharge, Point 3, Total Nitrogen (2008) 7-32Figure 7-31Wetland / Forest Discharge, Point 1 (Upstream), Total Phosphorus(2008) 7-32Figure 7-32 Wetland / Forest Discharge, Point 2, Total Phosphorus (2008) 7-33Figure 7-33 Wetland / Forest Discharge, Point 3, Total Phosphorus (2008) 7-33Figure 7-34 Total Nitrogen, Distribution of Wetland / Forest Discharge Impacts 7-35Figure 7-35Total Phosphorus, Distribution of Wetland / Forest DischargeImpacts 7-36Figure 8-1 Site 1 Entrance Outfall Conceptual Arrangement 8-7Figure 8-2 Site 2 Bridge Outfall Conceptual Arrangement 8-8Figure 8-3 Site 3 Revetment Wall Conceptual Arrangement 8-9Figure 8-4 Discharges from Woodburn Drain, March 2010 8-13LIST OF TABLESTable 2-1 BoM Data Statistics (November 2005 – February 2010) 2-16Table 2-2 Water Quality Indicator Data Collected by Council and DECCW 2-21Table 2-3 Default trigger values for slightly disturbed ecosystems insouth-east Australia (Adapted from Tables 3.3.2 and 3.3.3,chapter 3, ANZECC 2000) 2-23Table 2-4Table 2-5Draft Chlorophyll/Turbidity Reference Values for NSW Estuariesprovided by DECCW (November 2009) 2-24Evans Head STP Treated Effluent Flow and Quality Data(June 2008 to Sept 2009) 2-31Table 3-1 Comparison of Tidal Planes (MHL, 2006) 3-12Table 3-2Identified Values and Potential Pressures Resulting from theDischarge 3-28Table 4-1 Functional Units Used in WaterCAST Based on Land Use Type 4-4Table 4-2 Land Use Area Breakdown 4-5Table 4-3 Estimated Total Flows from Evans River and via Tuckombil Canal 4-9G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

LIST OF TABLESXTable 4-4 Mean Annual Flows by Land Use 4-10Table 4-5Estimated Total Annual and Mean Flows from Evans RiverCatchment and Tuckombil Canal (2000 –2009) 4-10Table 5-1 Broad Site Suitability Analysis for Wetland Forest Locations 5-9Table 5-2 Average Inflow Characteristics from Evans Head STP to Wetland 5-11Table 5-3 Assumed Wetland Configuration for Modelling 5-11Table 5-4 Comparison of Potential Rate Constants 5-12Table 5-5 Adopted Background Concentrations (C*) for Wetland Treatment 5-12Table 5-6 Summary Statistics for SILO MEDLI Climate Data 5-14Table 5-7 MEDLI Soil Parameters 5-17Table 5-8 MEDLI Soil Parameters (Continued) 5-18Table 5-9 MEDLI Models and Iterations 5-21Table 5-10 DSM Virus Input Data 5-22Table 5-11 Source of Time Series Results for Wetland Forest Modelling 5-23Table 5-12Table 6-1Net changes in Water Balance and Pollutant Load Dischargesfrom Selected Wetland / Forest Sites 5-26Evans River RMA Model Material Categories and AssociatedRoughness 6-8Table 6-2 Results of the RMA Model Continuity Check 6-22Table 7-1 Ambient Velocity Categorisation 7-6Table 7-2 Ambient Channel Geometry 7-7Table 7-3 Effluent Flow Rate Categorization 7-7Table 7-4 Diffuser Discharge Velocities 7-8Table 7-5 CORMIX Dilution Factor Reference Matrix 7-9Table 7-6Table 7-7Median Concentrations and Modelled Increases for ContinuousDischarges 7-21Median Concentrations and Modelled Increase for Ebb-TideDischarges 7-22Table 7-8 MEDLI Predicted Reductions in Runoff and Pollutant Loads, 2008 7-29Table 7-9 WaterCAST Predicted Upper and Total Catchment Loads, 2008 7-29Table 7-10 Median Concentrations and Modelled Results for Wetland /Forest Discharges 7-34Table 8-1Key Physical Features at the Ebb-Tide and ContinuousRelease Sites 8-4Table 8-2 Multi-Criteria Impact Risk Assessment Matrix 8-24G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

GLOSSARYXIGLOSSARYAccretionADANZECCBODChl-aCORMIXDECCWDEMDilution factorDINDODONEbb-tideECEutrophicationEVFar FieldFlood TideFRPHDHHW (SS)ISLWkg/m 3m AHDm/sm 2 /sm 3 /smg/LMLDMLWSmmNear fieldNeap tideNH 3NO 2NO 3NOxPSUREREDDRMA10sSCUBASIGNALSinuositySpring tideSTPTDNTNBuild up of material, e.g. sand as a result of coastal or fluvial processesAdvection-DispersionAustralia and New Zealand Environment and Conservation CouncilBiological Oxygen DemandChlorophyll-aMixing zone model used to predict and assess impacts of continuous point source dischargeto surface waterDepartment of Environment, Climate Change and WaterDigital Elevation Modelvolumetric ratio of ambient water to effluent within a mixing regionDissolved Inorganic Nitrogen (i.e. Ammonia + Nitrogen Oxides)Dissolved OxygenDissolved Organic Nitrogen (found in complex forms i.e. amino acids, proteins, urea andhumic acids)The outgoing tide from an estuaryElectrical ConductivityRefers to an increase in the rate at which organic material is supplied to an estuaryEnvironmental Valuearea of mixing region dominated by the ambient turbulent diffusion, i.e., ambient velocity andchannel geometryThe incoming tide to an estuaryFilterable Reactive Phosphorus (also Orthophosphate)HydrodynamicHigher High Water (Summer Solstice) ElevationIndian Spring Low Water. This is the lowest level, for most practical purposes, which the tidefalls. Only in exceptional circumstances will the tide fall lower.kilograms per cubic metreElevation relative to Australian Height Datum in metersmeters per secondsquare metres per secondcubic metres per secondmilligrams per litreMillion litres per dayMean Low Water Surface Elevationmillimetresarea of mixing region dominated by the initial momentum of dischargeThe tides which happen near the first and last quarter of the moon, when the differencebetween high and low water is less than at any other part of the month.Chemical nomenclature for AmmoniaChemical nomenclature for NitriteChemical nomenclature for NitrateAbbreviation to represent sum of Nitrite and NitratePractical salinity unitsRegional EcosystemRegional Ecosystem Description DatabaseFinite element hydrodynamic and advection dispersion modelSelf Contained Underwater Breathing ApparatusStream Invertebrate Grade Number Average LevelRefers to highly curved sections representing sinusoidal wave formThe tides which happen at, or soon after, the new or full moon, which rises higher thancommon tides. Spring tides have the greatest range.Sewage treatment plantTotal Dissolved Nitrogen (TDN) is sum of DIN and DONTotal NitrogenG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

GLOSSARYXIITPTrophicTSSUSEPAWaterCASTWQOWSETotal PhosphorusRefers to the rate at which organic material is supplied to estuariesTotal Suspended SolidsUS Environmental Protection AgencyeWater catchment model, later version of E2Water Quality ObjectiveWater Surface ElevationG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXIIIEXECUTIVE SUMMARYIn 1995, Richmond Valley Council (‘Council’) and the Department of Land and Water Conservation(now Department of Environment, Climate Change and Water, DECCW) recognised the need toinvestigate strategies to improve the Woodburn-Evans Head wastewater system. Initially thisinvolved the upgrade of the existing Evans Head Sewage Treatment Plant (STP) to improvedischarge water quality and the capacity of the plant. Furthermore, DECCW identified the need forconsideration of alternative options for discharge of the treated effluent, as the release of effluent toSalty Lagoon was no longer regarded as an acceptable long-term solution.In this regard, a number of effluent management strategies have been investigated which can broadlybe divided into reuse and disposal (of excess treated effluent) options. Council has identified variouseffluent disposal and/or reuse options to divert STP discharges from Salty Lagoon. Options whichare currently considered to be potentially viable include:• Dry weather open space irrigation in Evans Head and Woodburn;• Deep well injection;• Wetland and carbon sequestration forest with wet weather discharge to Evans River; and• Discharge to Evans River.Cost, environmental and social considerations have been identified by Council as critical factors inthe selection of the preferred option.In 2009, Council engaged BMT WBM to investigate the effect of disposing treated effluent from theEvans Head STP to the Evans River, to address the questions of:• The ability of the Evans River estuary to accept and assimilate or dissipate STP effluentdischarges; and• The impact of STP discharges on the environmental and social values of the Evans Riversystem.The outcomes of the investigation will further enhance Council’s understanding of the impact risk ofthese disposal options, and will fulfil the Pollution Reduction Program (PRP) 6 requirements outlinedin the Evans Head STP Licence with DECCW. PRP 6 is restated as follows,“To assist in considering the feasibility of effluent disposal locations, the Licensee mustundertake hydrodynamic and water quality modelling of the Evans River system. Theassessment needs to address the proposed locations for effluent discharge. A reportshould be prepared and submitted to DECCW.”This study has developed and assessed a number of discharge scenarios, including:• Ebb-tide release scenarios (various locations);• Continuous release scenarios (various locations); and• Wetland and carbon sequestration forest polishing release scenarios (various locations).G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXIVAssessments performed for the impact risk assessments have focused on the ultimate, i.e. 2050flows and quality from the upgraded STP. To enable assessment of the estuarine discharges, BMTWBM has developed (amongst others) linked hydrodynamic (HD) and advection/dispersion (AD)models. These models have been used to assess the relative contributions of total nutrients as aresult of various discharge scenarios to the estuary. The models allow for interrogation of resultswithin the estuary and immediately offshore.The following sections outline activities (particularly modelling) which have been completed by BMTWBM as part of this investigation. Figure 1 provides a schematic showing the linkages between thevarious modelling elements.Catchment Model(WaterCAST) –Inputs rainfall,evaporation,topographyOutputs – catchmentflows to estuaryHydrodynamicModel – Inputs,ocean tides,catchment flows,wind, bathymetryOutputs – calibrated modelwhich captures watermovements within estuaryAdvectionDispersion Model –Inputs HD model,salinity recovery dataOutputs – calibratedmodel that capturesmixing / flushing ofpollutants within estuaryOutputs – AD / HD modelsbetter represent near fieldmixing and pollutantevolutionDiffuser conceptdesign + CORMIX –Inputs – diffuser,channel geometry,tidal currents,discharge detailsWetland Models –Inputs wetlandconceptual design,soils data, rainfall,evaporation,cropping dataOutputs – time-series offlow/load from wetland /forest to estuaryScenarioAssessmentsInputs – STPflows/loads, Wetlandflows/loadsFigure 1 Linkages between Project ElementsG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXVParameter/StatisticImpact risks of options have been identified by comparison of predicted water quality as a result ofthe various discharge options (discussed further below) against previously established water qualityobjectives (discussed further below) for the Evans River estuary. Additionally, other social and/orenvironmental impact risks have been documented along with a review of the engineering sitelimitations and risks posed by various discharge locations and types.A preferred scenario (if one exists) could then be progressed by Council to detailed concept designstage to allow for final environmental approvals, concept costing, etc to be completed. This wouldallow for the preferred scenario to be compared with other potentially viable options for effluentdischarge, which is essential for any future stakeholder consultation.Evans Head STP Effluent QualityStatistical analysis of STP effluent data (flow and quality) is presented in Table 1. These data havebeen used as the basis for defining the quality of future discharges to the estuary or wetland / forestsystem. Predicted analysis of likely flow regimes for future discharge scenarios have been developedby Hydrosphere (2010) for use in this study. Based on observations of other STP discharges, theEvans Head STP effluent may have a characteristic odour, although the presence, characteristicsand strength of this odour have not been defined or assessed as part of this investigation.Table 1 Evans Head STP Treated Effluent Flow and Quality Data (June 2008 to Sept 2009)TotalNitrogenAmmonia Nitrate NitriteTotalPhosphorusTotalSuspendedSolidsBiologicalOxygenDemandFaecalColiformsUnits mg/L mg/L mg/L mg/L mg/L mg/L mg/L Cfu/100mL pH units ML/dayMedian 5.10 0.31 3.40 0.14 0.205 8.0 1.0 2.0 7.0 1.37Average 5.55 0.58 3.64 0.32 0.238 8.6 1.2 4.7 6.9 1.5510th perc. 3.70 0.15 2.00 0.04 0.110 4.0 0.0 0.0 6.7 1.0490th perc. 7.37 1.27 4.66 0.25 0.347 15.6 3.0 8.8 7.2 2.22Maximum 21.00 4.00 20.40 4.81 0.820 25.0 5.0 50.0 7.3 5.03Count 64 64 63 64 64 63 64 63 63 473pHFlowWater Quality ObjectivesThe Australian and New Zealand Environment and Conservation Council (ANZECC, 2000) guidelinesprovide default trigger values for slightly disturbed ecosystems in south-east Australia. These defaulttrigger values are recommended for use where no locally specific guideline values exist and areprovided in Table 2. For analysis of model results outside of the estuary (i.e. Airforce beach) themarine objectives apply.Table 2 Default trigger values for slightly disturbed ecosystems in south-east Australia(Adapted from Tables 3.3.2 and 3.3.3, chapter 3, ANZECC 2000)Ecosystem Chl-a Turbidity TP Sol P TN NOx NH 4 DO pHtype OEstuaries v(µg/L)4(NTU)0.5-10(mg/L)0.03(mg/L)0.005(mg/L)0.30(mg/L)0.015(mg/L)0.015(%sat)80-110 7.0-8.5Marine e1 na 0.025 0.01 0.12 0.005 0.015 90-110 8.0-8.4G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXVIOverview of Evans River Catchment and EstuaryThe catchment of the Evans River is approximately 92 km 2 (excluding water areas) and is mostlycomprised of forests (75%). Grazing in the upper reaches occupies approximately 11% of thecatchment, with other forms of agriculture, intensive uses, urban and rural residential lands, etccomprising the remaining 14% of the catchment.The Evans River itself commences at the Tuckombil weir, some 16km from the mouth of the estuary.The estuary is tidal for its full length and has a number of minor tributaries, such as Brandy ArmCreek. The Evans River joins the ocean at Evans Head, where twin breakwaters were constructed inthe 1960’s to aid boating navigation into and out of the estuary.Currently there is no active oystering or commercial fishing within the estuary, although somecommercial offshore fishing vessels moor within the Evans Head boat harbour which is within theEvans River estuary. The Evans River estuary is popular for a variety of recreational pursuitsincluding passive recreation, fishing, boating and swimming; generally consistent with other estuariesalong the northern NSW coastline. Evans Head is home to an aged demographic (compared to theNSW state average) and is a popular holiday destination.Key Processes Influencing Estuarine ConditionEstuarine water quality and ecology are a function of several influencing factors including catchmentconditions, entrance conditions, sedimentary processes and the key hydrodynamic factors of tidesand floods. Some of these processes can and have been influenced by the actions of man in theEvans River catchment and estuary.As noted above, the catchment of the Evans River is largely forested, and this typically correlates withlower loads of sediments and nutrients being discharged from the catchment in comparison to acatchment subject to other more intensive land-uses. However, areas of agricultural production existin the upper estuary near Woodburn, while urban and rural residential areas exist in the mid- to lowerestuary. Overflows from the Rocky Mouth Creek and Richmond River, via the Tuckombil weir andcanal, have been observed to significantly affect estuarine hydrodynamics and water quality. Prior tothe construction of the fixed height Tuckombil weir in 2001, the upper estuary was noted to have ahistory of poor water quality punctuated by numerous fish kills after flood events. The current fixedheight weir has changed drainage patterns in the upper estuary and appears to have largelyprevented these fish kills from occurring.The entrance of the Evans River estuary had breakwaters constructed in the 1960’s. Entranceconditions are now likely to be in a form of dynamic equilibrium with a net inflow of sand during drierperiods and erosion occurring during flood periods. A relatively stable entrance shoal is reported tohave established (PBP, 1999a), however, further investigation would be required to quantify sedimentbudgets in the entrance zone and identify if there is any net change in shoaling in the lower estuary.Tides constitute one of the key driving processes of the Evans River estuary and dominate estuarinehydrodynamics during dry weather periods. Flooding has been observed to dominate estuaryhydrodynamics on occasions, such as for the large flood event of early 2008 and again in May 2009.Tidal ranges decrease with increasing distance from the entrance bar to approximately where BrandyArm Creek meets the Evans River as a result of hydraulic losses associated with bed friction andG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXVIIother hydraulic losses. The upper sections of the estuary between the Brandy Arm Creek confluenceand Tuckombil weir appear to be hydraulically efficient and there is no significant reduction in tidalranges through this zone. Tidal phasing (i.e. difference in timing between slack tides and peakdischarges) is evident in the river. Tidal flushing is reported (PBP, 1999a) to increase from less than3 days in the lower estuary (up to Iron Gates) up to greater than 70 days at the far upstream end ofthe estuary.In terms of fluvial sedimentary processes, active accretion is reported (PBP, 1999a) to be occurringbetween Iron Gates and the Elm Street Bridge, although the rate may be quite small. This sedimentis likely to be sourced from the erosion of riverbanks and bed between Brandy Arm Creek and IronGates. This indicates that tidal hydrodynamics may continue to alter upstream of Iron Gates until astable river form is achieved. The lower estuarine hydrodynamics will be influenced by entranceconditions such as the entrance bar and shoal, although the system is believed to be dynamicallystable within a range of influences (i.e. flood, tides, etc).Water quality in the estuary generally exhibits a quasi-linear trend from near oceanic water qualityconditions at the downstream end, to a condition more defined by catchment inflows at the upperend. The quasi-linear trend along the estuary during periods of dry weather is governed by the tideand during these periods of low catchment flows, upstream water quality conditions can besignificantly improved. However, during periods of catchment inflows water quality conditions canworsen throughout the estuary, but most noticeably at the upper end of the estuary.For example, Figures 2 and 3 show time-series of total nitrogen (TN) and total phosphorus (TP) datarecorded by Council within the Evans River estuary. It is noted that there were numerous minorcatchment floods during the recording period, these typically did not result in weir overtopping.However, there was a large weir overtopping event in January 2008. The substantially increasedlevels of total nitrogen and total phosphorus are evident in the recorded water quality data, indicatingthe significant impact that overflows can have on estuarine water quality. Site 1 is at the tidal limit ofthe estuary, Site 2 is in the upper estuary, Site 3 is in the mid-estuary, Site 4 is in the lower estuaryand Site 5 is near the entrance.3.002.50TN (mg/L)2.001.501.000.500.00Aug 06Sep 06Oct 06Nov 06Dec 06Jan 07Feb 07Mar 07Apr 07May 07Jun 07Jul 07Aug 07Sep 07Oct 07Nov 07Dec 07Jan 08Feb 08Mar 08Apr 08May 08Jun 08Jul 08Aug 08Sep 08Oct 08Nov 08Dec 08Jan 09Feb 09Site 1 Site 2 Site 3 Site 4 Site 5Figure 2 TN Time Series, August 2006 to February 2009 (Source Council)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXVIII0.400.350.300.250.200.150.100.050.00Aug 06Sep 06Oct 06Nov 06Dec 06Jan 07Feb 07Mar 07Apr 07May 07Jun 07Jul 07Aug 07Sep 07Oct 07Nov 07Dec 07Jan 08Feb 08Mar 08Apr 08May 08Jun 08Jul 08Aug 08Sep 08Oct 08Nov 08Dec 08Jan 09Feb 09TP (mg/L)Site 1 Site 2 Site 3 Site 4 Site 5Figure 3 TP Time Series, August 2006 to February 2009 (Source Council)Monitoring completed by Council and DECCW, in the upper estuary did not achieve all of theDECCW or ANZECC annual median guideline trigger values for chlorophyll-a, TN, TP and turbidity.The mid- to lower estuary water quality monitoring results consistently achieved the guideline triggervalues. The water quality objectives (WQOs) utilised in the study are included in Table 1 and medianvalues calculated using water quality data collected by Council over 2008 are included in Tables 4, 5and 6. The location and extent of the exceedences of WQOs can be determined from these graphs.Catchment ModellingPrincipally to assist in the development of the hydrodynamic model, BMT WBM established aWaterCAST catchment model to predict flows from the catchment to the Evans River estuary.Catchment load predictions were also developed, but were not required for use in the advectiondispersionmodelling due to the modelling approach adopted.The flows were input to the hydrodynamic model to allow for its calibration and validation and toensure that key driving mechanisms of tides and catchment runoff were accurately represented.The WaterCAST model was built using the best available local climatic and topographic informationand parameterised using generally accepted factors for hydrology (and water quality). However,there was insufficient information available to fully calibrate the model.The catchment model also included overflows from Rocky Mouth Creek into the Evans River via theTuckombil Weir/Canal. As part of this project BMT WBM purchased available tide height informationfrom Manly Hydraulics Laboratory (MHL) at a number of locations in the estuary. Data from theirrecording station immediately adjacent to the Tuckombil weir was used to estimate weir overflowsusing previously obtained channel cross-section information for the Tuckombil Canal.Figure 4 represents catchment model and weir flow estimates from 2000 to 2009. It can be seenfrom this figure that the Tuckombil overflows can be significant and can exceed catchment runofflevels in certain years. It is noted that there are some limitations in the approach used to determineweir overflows, in that a more sophisticated hydraulic model would provide a more accurate estimateG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXIXof weir overflows for very large events (i.e. where the weir is likely to drown out due to flood tailwatereffects). Development of such a hydraulic model was outside the scope of this study.300,000250,000Evans River Catchment Tuckombil Canal Rainfall2,5002,000ML/Year200,000150,000100,00050,0001,5001,000500Rainfall (mm)‐2000 2001 2002 2003 2004 2005 2006 2007 2008 2009Year‐Figure 4 Estimated Annual FlowsHydrodynamic and Advection Dispersion ModellingThe hydrodynamic model (HD) was established across the entire estuary, extending out well past theentrance to capture the effect of water being discharged from and returning to the estuary across thetidal cycle.The hydrodynamic model was calibrated to field data collected by BMT WBM between 31/01/2010 to19/02/2010 and validated across 01/11/2005 to 31/05/2006 to data collected by MHL.The advection-dispersion (AD) model operates within the model extent developed for the HD model(i.e. across the entire estuary and extending out past the entrance). The AD model was calibratedbetween 21/07/2006 to 31/12/2006 using available Council collected electrical conductivity datawithin the Evans River. The approach used was to reproduce salinity recovery rates after specificrainfall events.For scenario modelling the period between 1/1/2008 to 31/12/2008 was used for assessment. Thisencompassed a period of best available data and was suitable for calculation of annual medianconcentrations, consistent with comparison with chronic (i.e. long term) water quality objectives.As discussed in the catchment modelling section, there remains some uncertainty with the catchmentinflows and to some extent with the bathymetric data, however, the hydrodynamic model was foundto reproduce the major hydrodynamic features of the Evans River estuary.Overall, the models were successfully calibrated and/or validated and were deemed suitable for usein the assessments required by the study.CORMIX ModellingTo better represent the movement of pollutants from a discharge location (i.e. pipe / diffuser) into theestuary it is necessary to model the near field (i.e. diffuser and mixing zone) and input informationG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXfrom this model into the AD model (i.e. far field model). If this linkage is not applied, plume evolutionwould not be accurately captured and water quality predictions would likely be inaccurate in the nearto mid zones around the discharge.CORMIX was used to determine the initial dilution (i.e. mixing of discharge) into receiving water asthe result of the initial momentum of discharge. To do this, BMT WBM has proposed a diffuserarrangement, conceptually developed to achieve the greatest diffusion. The diffuser was up to 20mlong with three ports of 100mm diameter. The diffuser has initially been assumed to sit on the bottomof the channel perpendicular to the direction of the currents. Diffuser ports were oriented downstreamat a vertical angle of 30 degrees incident to the bottom of the channel. Based on this port elevationwas 0.5 m above the manifold (i.e. channel bed).Continuous and Ebb-Tide Discharge ModellingThree potential diffuser sites were adopted including the bridge (Elm St), a location on the northernrevetment wall and one near the entrance of the estuary as shown in Figure 5. Appropriate channelproperties at these locations were input to the CORMIX model.Figure 5 Continuous and Ebb-Tide Discharge LocationUsing the assumed diffuser design, specifics of the channel geometry, range of tidal currents,discharge flow rates and discharge qualities (provided by Council) at the adopted discharge locations,CORMIX was used to develop a three-dimensional ‘lookup’ table. This table was looked updynamically by the AD model to alter the inserted flow rate and constituent concentrations based onthe calculated diffusion rates.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXIWetland Carbon Sequestration Forest ModellingPrevious studies by the Water and Carbon Group (WCG) had identified the feasibility of using aWetland/Carbon Sequestration Forest to polish STP effluent prior to discharging it to the Evans River.BMT WBM have utilised this conceptual design developed by WCG to remodel the system to providethe necessary time-series of flows and pollutants to the Evans River. It is constituted of a free watersurface wetland for effluent polishing with effluent irrigation of a 125 ha wetland forest intended to beoperated for carbon sequestration as shown in Figure 6.Figure 6 Schematic of Wetland / Forest Discharge OptionFollowing an initial review of the modelling process adopted in WCG (2009), a methodology wasdeveloped to undertake a more detailed and dynamic mass balance modelling process to provide arepresentative time-series for use in AD scenario modelling.Potential wetland / forest discharge locations were developed as shown in Figure 7 and relevant sitespecific information e.g. soil properties, were applied in modelling. A preliminary site feasibilityassessment has ruled out potential wetland / forest sites near Doonbah Village and Iron Gates, onthe basis of there being insufficient land area available that is not already reserved for othersignificant uses e.g. National Park. Results for the Tuckombil Canal and Brandy Arm Creek sitesonly, are presented.Overall, the wetland / forest modelling indicated that the wetland / forest schemes were very effectiveat removing the nutrients contained in the STP effluent. Modelling also identified that discharges tothe Evans River from the forest (noting that the wetland rarely overflowed) were determined to occurwhen catchment rainfall filled soil moisture stores and lead to runoff events (similar to the surroundingcatchments). Discharges from the irrigated forest to the Evans River were assumed to be of thesame quality as those from surrounding forested catchments. This is to say that the Event MeanConcentration (EMC) of pollutants in the runoff from the wetland / forest were the same as thesurrounding forested catchments. Hence, any pollutant load reductions to the estuary resulting fromthe scheme are entirely a function of the changed water balance rather than any changes in landuse.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXIIFigure 7 Wetland / Forest Discharge LocationsDaily time-series of hydraulic and nutrient loads discharging to the Evans River from the wetland /forest were derived from the modelling results, and are shown in Figures 8, 9 and 10 with summarydata provided in Table 3.The “Existing” data presented in Figure 8 represents an existing forested site without a STP wetland /forest scheme present. The assumed landuse for the potential future case which involves theimplementation of a STP wetland / forest was also forest. It can be seen from Figure 8 that theexisting sites have slight differences in the water balance, with typically greater levels of evapotranspirationand surface runoff occurring in the Tuckombil Canal site. The Brandy Arm Creek sitewas predicted to have greater levels of deep drainage. These differences are a function of variancesin soil properties (i.e. soil storage capacity, hydraulic conductivity, etc) between the two sites.Figure 9 provides insight into the relative impact on the water balance at each location associatedwith the implementation of the scheme. It has been predicted that the implementation of the schemewill significantly increase evapo-transpiration rates for both sites (Tuckombil Canal greater thanBrandy Arm), it will slightly increase deep drainage (Brandy Arm greater than Tuckombil Canal) and itwill lead to slight decreases in surface runoff (similar magnitude of reduction at both sites).The changes in predicted evapo-transpiration rates vary between sites largely due to differences insoil water storage capacity. Higher soil storage capacity provides greater opportunities for effluent tobe available for plant uptake and evaporation. Similarly, runoff volumes vary as a result ofdifferences in soil storage capacity and hydraulic conductivity which affects the quantity of waterwhich runs off to the estuary or which goes into groundwater stores.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXIII2500Evapo-transpiration Deep Drainage Runoff20001500mm/year10005000Tuckombil Canal ExistingTuckombil Canal withSTP Wetland / ForestBrandy Arm CreekExistingBrandy Arm Creek withSTP Wetland / ForestFigure 8 Water Balance for Selected STP Wetland / Forest Sites1000Evapo-transpiration Deep Drainage Runoff800600mm/year4002000-200Tuckombil CanalBrandy Arm CreekFigure 9 Net Changes in Water Balance for Selected Wetland / Forest SitesG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXIV300TNTP200100kg/year0-100-200-300Tuckombil CanalBrandy Arm CreekFigure 10Net Changes in Total Nutrients Loads for Selected Wetland / Forest SitesFigure 10 identifies that due to the predicted reductions in surface runoff (as shown in Figure 9) fromthe wetland/forest sites, there is a corresponding net reduction in total nutrient loads discharged tothe Evans River estuary.Table 3 Net changes in Water Balance and Pollutant Load Discharges from Selected Wetland/ Forest SitesEvapotranspirationDeepDrainageSurfaceRunoffLocationTN Load TP Loadmm/year mm/year mm/year kg/year kg/yearTuckombil Canal 645 31 -50 -244 -7Brandy Arm Creek 552 120 -51 -211 -6Connectivity between shallow groundwater and the Evans River is yet to be investigated in any detail.Similarly, the impact on long-term groundwater elevation of irrigation on the sites has not beenestimated.Receiving Water Scenario ModellingFigures 5 and 7 show the locations of continuous (i.e. 24 hr per day discharge) / ebb-tide (6 hr perday discharge) and wetland / forest releases, respectively.For these scenarios, the identified flows and loads from the effluent transfer system (in the case ofthe ebb-tide / continuous release) and wetland / forest models have been used as inputs to the ADmodel. Information from the AD model has been obtained by extracting time-series of information atlocations shown in Figure 11.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXVFigure 11Model Data Extraction LocationsAll discharge results have been calculated as a change in concentration above the backgroundambient concentrations of total nitrogen and total phosphorus.The process used to calculate the total modelled concentration at a given data extraction point hasbeen to determine the maximum value of modelled daily maximums during a two-week period aroundeach Council sampling event in 2008. This incremental value was then added to the backgroundambient median concentration within the estuary (calculated from available Council data over thescenario modelling period, i.e. 1/1/2008 to 31/12/2008). Since there were 5 Council monitoring sitesfor water quality and there were 8 data extraction points, conservative assumptions were appliedbased on proximity of extraction points to monitoring sites to effect these additions.Table 4, 5 and 6 show this information. The column labelled ‘Measured Background Concentration’represents the calculated or interpolated median ambient water quality condition at the dataextraction location. The column labelled ‘Incremental Concentration Increase’ represents expectedincreases predicted by the AD modelling and represents the component of pollutant added by theSTP discharge. The column labelled ‘Predicted Resultant Concentration’ represents the summationof the column ‘Measured Background Concentration’ with the column ‘Predicted ResultantConcentration’. Release locations are represented in the rows as per Figures 5 and 7.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXVITable 4 Median Concentrations and Modelled Increases for Continuous DischargeData ExtractionLocation andDischarge OptionMeasured BackgroundConcentrationTNmg/LTPmg/LIncremental ConcentrationIncrease bTNmg/LTPmg/LPredicted ResultantConcentrationTNmg/LWQO 0.30 0.03 Default Trigger Values for Estuary Ecosystem aData Extraction Point 1Background 0.675 0.060TPmg/LEntrance 0.007 (1%) 0.000 (0%) 0.682 0.060Bridge 0.009 (1%) 0.000 (0%) 0.684 0.060Revetment 0.008 (1%) 0.000 (0%) 0.683 0.060Data Extraction Point 2Background 0.635 0.028Entrance 0.007 (1%) 0.000 (0%) 0.642 0.028Bridge 0.010 (2%) 0.000 (0%) 0.645 0.028Revetment 0.009 (1%) 0.000 (0%) 0.644 0.028Data Extraction Point 3Background 0.635 0.028Entrance 0.011 (2%) 0.000 (0%) 0.646 0.028Bridge 0.015 (2%) 0.001 (4%) 0.650 0.029Revetment 0.014 (2%) 0.000 (0%) 0.649 0.028Data Extraction Point 4Background 0.430 0.030Entrance 0.016 (4%) 0.000 (0%) 0.446 0.030Bridge 0.023 (5%) 0.000 (0%) 0.453 0.030Revetment 0.019 (4%) 0.000 (0%) 0.449 0.030Data Extraction Point 5Background 0.250 0.025Entrance 0.010 (4%) 0.000 (0%) 0.260 0.025Bridge 0.016 (6%) 0.001 (4%) 0.266 0.026Revetment 0.013 (5%) 0.001 (4%) 0.263 0.026Data Extraction Point 6Background 0.250 0.025Entrance 0.011 (4%) 0.000 (0%) 0.261 0.025Bridge 0.021 (8%) 0.001 (4%) 0.271 0.026Revetment 0.016 (6%) 0.001 (4%) 0.266 0.026Data Extraction Point 7Background 0.155 0.025Entrance 0.022 (14%) 0.001 (4%) 0.177 0.026Bridge 0.039 (22%) 0.002 (8%) 0.194 0.027Revetment 0.030 (21%) 0.002 (8%) 0.185 0.027Data Extraction Point 8Background 0.155 0.025Entrance 0.021 (14%) 0.001 (4%) 0.176 0.026Bridge 0.034 (22%) 0.002 (8%) 0.189 0.027Revetment 0.033 (21%) 0.002 (8%) 0.188 0.027WQO 0.12 0.025 Default Trigger Values for Marine Ecosystem aData Extraction Beach Point 1Background NA c NA cEntrance 0.014 0.001 NA NABridge 0.012 0.001 NA NARevetment 0.013 0.001 NA NAValues in bold indicate concentrations in excess of objective(a) ANZECC 2000(b) Percentage increases were determined by dividing the incremental increase by the measured backgroundconcentration(c) No existing monitoring data available for the beach zone suitable to establish background conditionsG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXVIITable 5 Median Concentrations and Modelled Increase for Ebb-Tide DischargesData ExtractionLocation andDischarge OptionMeasured BackgroundConcentrationTNmg/LTPmg/LIncremental ConcentrationIncrease bTNmg/LTPmg/LPredicted ResultantConcentrationTNmg/LWQO 0.30 0.03 Default Trigger Values for Estuary Ecosystem aData Extraction Point 1Background 0.675 0.060TPmg/LEntrance 0.005 (1%) 0.000 (0%) 0.680 0.060Bridge 0.006 (1%) 0.000 (0%) 0.681 0.060Revetment 0.005 (1%) 0.000 (0%) 0.680 0.060Data Extraction Point 2Background 0.635 0.028Entrance 0.006 (1%) 0.000 (0%) 0.641 0.028Bridge 0.007 (1%) 0.000 (0%) 0.642 0.028Revetment 0.006 (1%) 0.000 (0%) 0.641 0.028Data Extraction Point 3Background 0.635 0.028Entrance 0.009 (1%) 0.000 (0%) 0.644 0.028Bridge 0.011 (2%) 0.000 (0%) 0.646 0.028Revetment 0.009 (1%) 0.000 (0%) 0.644 0.028Data Extraction Point 4Background 0.430 0.030Entrance 0.010 (2%) 0.000 (0%) 0.440 0.030Bridge 0.013 (3%) 0.000 (0%) 0.443 0.030Revetment 0.011 (3%) 0.000 (0%) 0.441 0.030Data Extraction Point 5Background 0.250 0.025Entrance 0.007 (3%) 0.000 (0%) 0.257 0.025Bridge 0.011 (4%) 0.000 (0%) 0.261 0.025Revetment 0.008 (3%) 0.000 (0%) 0.258 0.025Data Extraction Point 6Background 0.250 0.025Entrance 0.007 (3%) 0.000 (0%) 0.257 0.025Bridge 0.018 (7%) 0.001 (4%) 0.268 0.026Revetment 0.010 (4%) 0.000 (0%) 0.260 0.025Data Extraction Point 7Background 0.155 0.025Entrance 0.013 (8%) 0.001 (4%) 0.168 0.026Bridge 0.052 (34%) 0.003 (12%) 0.207 0.028Revetment 0.022 (14%) 0.001 (4%) 0.177 0.026Data Extraction Point 8Background 0.155 0.025Entrance 0.014 (9%) 0.001 (4%) 0.169 0.026Bridge 0.040 (26%) 0.002 (8%) 0.195 0.027Revetment 0.040 (26%) 0.002 (8%) 0.195 0.027WQO 0.12 0.025 Default Trigger Values for Marine Ecosystem aData Extraction Beach Point 1Background NA c NA cEntrance 0.014 0.001 NA NABridge 0.013 0.001 NA NARevetment 0.013 0.001 NA NAValues in bold indicate concentrations in excess of objective(a) ANZECC 2000(b) Percentage increases were determined by dividing the incremental increase by the measured backgroundconcentration(c) No existing monitoring data available for the beach zone suitable to establish background conditionsG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXVIIITable 6 Median Concentrations and Modelled Increases for Wetland / Forest DischargeData ExtractionLocation andDischarge OptionMeasured BackgroundConcentrationTNmg/LTPmg/LIncremental ConcentrationIncrease b cTNmg/LTPmg/LPredicted ResultantConcentrationTNmg/LWQO 0.3 0.03 Default Trigger Values for Estuary Ecosystem (a)Data Extraction Point 1Background 0.675 0.060TPmg/LTuckombil Canal -0.068 (-10%) 0.000 (0%) 0.607 0.060Brandy Arm Ck -0.002 (0%) 0.000 (0%) 0.673 0.060Data Extraction Point 2Background 0.635 0.028Tuckombil Canal 0.000 (0%) -0.001 (-4%) 0.635 0.027Brandy Arm Ck -0.013 (-2%) 0.000 (0%) 0.622 0.028Data Extraction Point 3Background 0.635 0.028Tuckombil Canal 0.000 (0%) 0.000 (0%) 0.635 0.028Brandy Arm Ck -0.008 (-1%) 0.000 (0%) 0.627 0.028Data Extraction Point 4Background 0.430 0.030Tuckombil Canal 0.000 (0%) 0.000 (0%) 0.430 0.030Brandy Arm Ck -0.004 (-1%) 0.000 (0%) 0.426 0.030Data Extraction Point 5Background 0.250 0.025Tuckombil Canal -0.004 (-2%) 0.000 (0%) 0.246 0.025Brandy Arm Ck -0.003 (-1%) 0.000 (0%) 0.247 0.025Data Extraction Point 6Background 0.250 0.025Tuckombil Canal -0.005 (-2%) 0.000 (0%) 0.245 0.025Brandy Arm Ck -0.003 (-1%) 0.000 (0%) 0.247 0.025Data Extraction Point 7Background 0.155 0.025Tuckombil Canal 0.000 (0%) 0.000 (0%) 0.155 0.025Brandy Arm Ck -0.003 (-2%) 0.000 (0%) 0.152 0.025Data Extraction Point 8Background 0.155 0.025Tuckombil Canal -0.007 (-5%) 0.000 (0%) 0.148 0.025Brandy Arm Ck -0.003 (-2%) 0.000 (0%) 0.152 0.025WQO 0.12 0.025 Default Trigger Values for Marine Ecosystem (a)Data ExtractionBeach Point 1Background NA d NA dTuckombil Canal 0.000 0.000 NA NABrandy Arm Ck 0.000 0.000 NA NAValues in bold indicate concentrations in excess of objective(a) ANZECC 2000(b) Percentage increases were determined by dividing the incremental increase by the measured backgroundconcentration(c) Modelling approach adopted for wetland / forest scheme provides indicate results(d) No existing monitoring data available for the beach zone suitable to establish background conditionsG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXIXKey findings and observation from the modelling included:• Nutrient concentrations downstream of each discharge location are generally increased abovethose in the upstream direction, as a result of tidal action (i.e. tidal exchange or flushing) carryingeffluent out of the estuary;• Ebb-tide discharges generally result in higher nutrient concentrations in the downstream directionand lower in the upstream direction, as more effluent is pushed towards the ocean on the ebbingtide, as opposed to continuous discharges which allow a greater proportion of effluent to carryupstream;• Predicted resultant TN concentrations increases/decreases are larger than those for TP, as thereare lower loads/concentrations of TP in the treated effluent being discharged via the ebb-tidecontinuous and wetland options;• A number of sites (mainly in the upper estuary) recorded ambient water quality conditions inexcess of the identified guideline trigger values. This outcome was independent of whether STPdischarges were included or not;• Discharges from the bridge results in larger increases in TN and TP at all data extraction points,than discharges at the entrance / revetment wall for both ebb-tide and continuous discharges.Discharges at entrance and revetment wall sites results in more rapid dispersion because of theimmediate mixing with the larger body of ocean water. Ebb-tide discharge demonstrates greaterdispersion as a result of the dose and rest cycling, allowing for the same amount of dispersion inthe absence of discharge during rest periods;• The greatest increase above background concentrations for the continuous and ebb-tide optionsis for an ebb-tide discharge from the bridge, which was calculated to be approximately 0.052mg/L TN at Data Extraction Point 7 (~ 34% above ambient conditions at that location). Thisoption also provided the greatest increase in TP concentrations which was determined to be0.003 mg/L (~ 12% above ambient conditions at that location);• Predicted resultant TN concentration increases in the mid to upper estuary (i.e. upstream of DataExtraction Point 5) indicates minor predicted nutrient increases of less than 6% abovebackground ambient concentrations for both ebb-tide and continuous releases;• In line with the effect of the wetland / forest scheme reducing net flows (and consequentlypollutant loads) to the estuary, modelling results indicate reductions in TN concentrations in thefar upper estuary (i.e. Data Extraction Point 1) for the Tuckombil Canal wetland / forest scheme.Negligible reductions in ambient nutrient concentrations were predicted as a result of theimplementation of Brandy Arm wetland / forest; and• There is insufficient available background water quality data for the beach location to predict aresultant concentration, however, in terms of incremental increases the wetland / forestdischarge provided no discernable increase at the beach, while the ebb-tide and continuousreleases (from all discharge locations) provided minor increases of up to 0.014 mg/L TN and0.001mg/L TP.To illustrate the effect of effluent being conveyed differently through the estuary on different tides,Figure 12 shows incremental increases in TN for a continuous entrance discharge during spring tideand neap tide events on 27 th July and 3 rd August 2008.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARY XXX0 hr8 hr flood0 hr8 hr flood2 hr ebb10 hr flood2 hr ebb10 hr flood4hr ebb12 hr flood4hr ebb12 hr flood6 hr ebb14 hr ebb6 hr ebb14 hr ebbFigure 12Incremental TN Concentrations Resulting from Continuous Release at Entrance - Neap Tide 27 July 2008 (left), Spring Tide 3 August 2008 (right)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXXIThe colouring within the images represents the incremental increases in TN concentrations resultingfrom the STP discharge. The dark blue shading (most commonly shown) represents the minimumincremental TN concentration of 0.005mg/L above background concentrations (incremental increasesbelow 0.005 mg/L have not been shown). The model had been running for the entire year of data(i.e. since 1/1/2008) prior to this data being extracted, and hence the model was sufficiently ‘warmedup’. The images show:• For both neap and spring tides, the incremental TN concentrations at the boundary are less than0.005 mg/L (as the images do not show discharges reaching the model boundary inconcentrations greater than this). Hence artificial losses of TN over the model boundary arelikely to be negligible. The ocean boundary selected appears to have been suitably located forthe purposes of these assessments;• An ebbing tide (i.e. outgoing tide) is unable to remove the entire TN mass within the estuary outto the ocean. Hence, this mass of TN is moved backward and forwards through the estuaryacross the ebbing and flooding tide; and• Spring tides result in greater distribution of the effluent throughout the upper estuary and out intothe ocean (when compared to a neap tide) as a result of the stronger tidal currents experiencedduring spring tides.Results for discharges on the ebb-tide were similar to those for the continuous release except thatless effluent gets conveyed upstream of the discharge point. However, some effluent does getconveyed upstream despite it being discharged from the estuary on the ebb-tide, a proportion returnsfrom the ocean on the next flooding tide.Social and Environmental Factors, Construction and OperabilityWater quality modelling provides an indication of potential risks to water quality related values, suchas protection of aquatic ecosystems, and associated risks for adverse biological responses e.g. algalblooms, etc. There are also a number of other factors which will influence the suitability of thedischarge scheme based on the potential impacts it may have on other social and environmentalvalues. Suitability of schemes also relate to the design, construction and operability risks it presents.Table 7 includes a multi-criteria impact risk assessment matrix which identifies key design,construction and operability considerations including:• Natural variability in bathymetry;• Increased water velocities;• Commercial and recreational interaction;• Waves and sand movement;• Construction of the pipeline and discharge infrastructure;• Discharge infrastructure fouling with marine growth; and• Saltwater corrosion of discharge infrastructure materials.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXXIITable 7 also identifies key environmental and social value risk areas, including:• Nature conservation values;• Cultural and heritage values;• Education and scientific values;• Scenic values;• Recreation and tourism values; and• Socio-economic values.Factors related to pipeline route land acquisition, wetland/forest scheme land acquisition andassociated approvals for the pipeline route, and wtland / forest site, and discharges to the estuaryhave not been considered in detail as part of this study. Consequently these have not been includedin the impact risk assessment.Multi-Criteria Impact Risk AssessmentMulti-criteria impact risk factors have been compared against the objectives established for them andprovide a determination of what degree of impact risk the factor presents for the discharge schemesbeing compared. It should be noted that not all risks could be quantified as part of this study, henceconservatively where risks are uncertain, these have been identified as a potential impact subject tofurther investigation as identified in the matrix. The colour coding presents an easy visual tool toassist in interpreting the impact risk outcome.A number of the discharge scenarios to the lower estuary provided similar performance in terms ofwater quality and also provided similar sets of impacts. Based on this, impact risk assessments havebeen limited to consideration of wetland / forest discharges (from the Tuckombil Canal and BrandyArm Creek sites) and ebb-tide and continuous releases from the revetment wall.The revetment wall discharge site is favoured over the entrance discharge option as it is likely topresent a more readily constructible option with lower construction risks and potentially costs. Therevetment wall site option provides for similar (albeit slightly lessened) water quality outcomes andprovides the added benefit of having a significant anchor point (i.e. the revetment wall) to secure anydischarge infrastructure, as opposed to what is likely to be a shifting sand bed on the bottom of theestuary for the entrance site. The revetment wall site is favoured over the bridge discharge site as itprovides the improved water quality outcomes due to increased dispersion/tidal exchange at thislocation. The bridge site also has discharge infrastructure closest to the water surface, presenting thegreatest potential opportunity for the general public to interact with it and observe its operation, bothof these factors present inherent risks.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXXIIIAspect Region / Value / Element ObjectiveWater Quality(total nutrientconcentrations)Physicalconsiderationsaffectingdesign andconstructionUpper estuaryLower estuaryGroundwaterNatural variability inbathymetryIncreased watervelocitiesCommercial andrecreational interaction• SnorkellingModelled conditionsnot to exceedANZECC guidelinetrigger vales fornutrientsEnsure dischargesfrom the irrigatedforest do notnegatively impactupon groundwaterquality and its usesEnsure that thedischargeinfrastructure(including pipeline)does not becomeexcessively coveredor exposedEnsure that risks ofshear stress failureare minimisedEnsure that theseexisting uses are notoverly compromisedWetland / Forest Discharge(Tuckombil Canal)Guideline trigger values for nutrients alreadyexceeded in upper estuary. The Tuckombil Canalsite discharge is predicted to result in a minorimprovement in TN concentrations in the farupper estuary (i.e. decrease in ambient TNconcentration). The reduction in nutrientsreduces risk of adverse biological effects (e.g.algal bloom) occurring in the upper estuary.Table 7 Multi-Criteria Impact Risk Assessment MatrixWetland / Forest Discharge(Brandy Arm)Neutral or possibly minor beneficial impact toexisting water quality. ANZECC guidelinetrigger values for nutrients already exceeded inupper estuary.No impact to existing water quality. ANZECC guideline trigger values are achieved in the lowerestuary.Modelling indicated reduced groundwater inflowsfrom the Tuckombil Canal wetland / forest sitewhen compared to the Brandy Arm Creek forest /wetland site. There remains a risk thatgroundwater quality in this zone may be impactedby the scheme and this remains an aspect forfurther detailed investigation.Modelling indicated increased groundwaterinflows from the Brandy Arm Creek forest /wetland site when compared to the TuckombilCanal wetland / forest site. There remains arisk that groundwater quality in this zone maybe impacted by the scheme and this remainsan aspect for further detailed investigation.There may be some active bank erosion and accretion in sections of the upper estuary although themagnitude of this risk is considered to be negligible.No discharge infrastructure to be located within the channel.No impactRevetment Ebb-Tide DischargeRevetment Continuous DischargeGuideline trigger values for nutrients already exceeded in upper estuary and both schemesare predicted to increase nutrient concentrations further. Ebb-tide releases were predictedto result in slightly lower concentrations than the continuous release in the upper estuary.Increasing nutrient concentrations further above the ambient (background) concentrationwhich already exceeds the ANZECC guideline trigger values further increases the risk ofadverse biological responses occurring (e.g. algal bloom).Discharges to the lower estuary provides the best environment for discharge mixing anddilution and the lower estuary has been demonstrated to have low ambient nutrientconcentrations and sufficiently high assimilative capacity to avoid exceedence of theguideline trigger values for nutrients. Further data collection is required to determine ifANZECC guideline trigger values will be exceeded on Airforce Beach, although theassessed incremental increases as a result of the STP discharge are very small.No impactThe entrance shoal which extends from the end of the breakwaters to immediatelydownstream of the Elm Street Bridge is actively shifting as a result of tides and floodmovements, presenting greater risk of scour and sedimentation of discharge infrastructure.Further assessment of the range of estuary bed movement is required to assist indetermining maximum depths at which discharge infrastructure can be placed.The revetment wall site provides a potentially solid foundation to mount the dischargeinfrastructure on to; however, it will still be exposed to high periodic stresses as a result ofhigh water velocities. It is considered that design should be able to limit potential impactsfrom high water velocities.There is some risk of water ingestion during snorkelling activities which may lessen anindividual’s willingness to undertake this activity, however, visibility is unlikely to be affected.• SCUBA diving No impact There is some risk of water ingestion during SCUBA diving which may lessen anindividual’s willingness to undertake this activity, however, visibility is unlikely to be affected.There is an increased risk of physical contact with the release infrastructure which may beencrusted in barnacles presenting an abrasion risk.• Swimming• Fishing• Poweredrecreational boating• Non-poweredrecreation boating• Commercial fishingcraft egress• Passive recreationThe discharge of STP effluent to the estuary may influence an individual’s perceptions of thecleanliness and safety of undertaking swimming within the estuary.Discharges unlikely to affect fish, however, there may be some perceptions of declining fish health orcatch.No impactNo impactNo impactNo impactThe discharge of STP effluent to the estuary may influence an individual’s perceptions ofthe cleanliness and safety of undertaking swimming within the estuary.Fish responses to the discharge have not been determined, although the limited increasesin nutrient concentrations indicate that any response would be minor. There may be someperceptions of declining fish health or catch as a result of the discharge.No impact. There may be some risk of catching an anchor on the discharge infrastructure.No impactBased on current information available for minimum tide levels, bed depths and the drafts ofboats which may use the entrance channel for egress to and from the ocean, the height ofthe discharge infrastructure does not provide sufficient freeboard to eliminate risk of contactand would be unacceptable. The use of appropriate channel markers may lessen this risk toa more acceptable level. Also, further definition of the range of estuary bed depths hasbeen recommended for further investigation to better define the maximum depth at whichthe discharge infrastructure can be located.The discharge of STP effluent may create a visual difference between the discharge andthe ambient water. Density differences between the effluent water and saline estuary waterwill result in effluent rising to the surface leading to the present of surface ripples part of thetime (most notable for continuous releases). Furthermore, the smell of treated anddisinfected effluent when discharged to the estuary may be noticeable to some persons asthe discharge plumes surfaces. Further investigation of this effect has been recommended.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYAspect Region / Value / Element ObjectiveOperationalconsiderationsaffectingdesign andoperationSocial andEnvironmentalValuesSand movementConstruction of thepipeline and dischargeinfrastructure(terrestrial)Construction of thepipeline and dischargeinfrastructure (aquatic)Discharge infrastructurefouling with marinegrowthSaltwater corrosion ofdischarge infrastructurematerialsNature conservationvaluesCultural and heritagevaluesEducation and scientificvaluesScenic valuesRecreation and tourismvaluesSocio-economic valuesEnsure that risks ofsand ingress areminimisedMinimise potentialconstruction risksMinimise potentialconstruction risksMinimise the risk ofmarine growthcausing operationalfailureMinimise the risk ofcorrosionMinimise impacts tothe natureconservation valuesof the estuaryMinimise impacts tothe cultural andheritage values ofthe estuaryMinimise impacts tothe education andscientific values ofthe estuaryMinimise risk to thescenic values of theestuaryMinimise impacts onrecreation potentialof the estuaryMinimise economicimpacts of theNo impactWetland / Forest Discharge(Tuckombil Canal)Wetland / Forest Discharge(Brandy Arm)Pipeline route distances to the wetland / forest site are likely to be considerable longer than those tothe lower estuary. Route selection should occur where possible to minimise social and orenvironmental impacts to cultural heritage, noise, air quality, traffic, relocation of existing services,surface and groundwater quality, vegetation, etc.No assessment of geotechnical or soil conditions, for the purposes of pipeline construction, wasmade as part of this study and remains a construction risk.The wetland / forest discharge may take the form of open channels which will not be subject tofouling. If submerged pipes are used, potential for fouling will need to be considered, although theextent of fouling in the upper estuary is unlikely to be as significant as the lower estuary due tochangeable salinity regimes limiting opportunities for marine organism growth.It is likely that concrete infrastructure can be used in the outlet structure for the wetland discharge.Corrosion resistant concrete and reinforcing should be considered for use.The Evans River catchment has a variety of terrestrial flora and fauna values. The siting of thewetland / forest and associated pipelines to this system or to lower estuarine discharge locationswould need to be cognisant of these terrestrial values. It has been assumed that pipeline routes andwetland / forest sites can be selected to mitigate potential risks / impacts in this regard.The pipeline and wetland / forest would need to be sited to avoid significant impact on these values,if any were identified in or adjacent the project footprint.The pipeline and wetland / forest would need to be sited to avoid impacting the subfossil coral reef(in Doonbah locality) as it has been recognised as being of significant scientific value.The wetland / forest system is likely to be sited a significant distance away from highly populatedareas. Furthermore the area will be forested and may not be distinguishable from surroundingareas.As for fishing and swimming above, there may be some perceptions of declining fish health or catchor unsafe swimming conditions. It is possible that these perceptions could be addressed throughmonitoring and public consultation.Reductions in an individual’s perceived ability to recreate within the estuary may impact on thetourism potential of the estuary, increasing the risk of socio-economic impacts.Revetment Ebb-Tide DischargeThe discharge location is within the activeentrance shoal. The associated movementof sand in this area presents a greater riskof sand ingress into the dischargeinfrastructure, and scour as a result offlooding. Design of ebb-tide releaseoutlets will need to be considered toreduce risk of sand ingress during restperiods. Anchoring to the revetment wallreduces flood scour risks.Revetment Continuous DischargeXXXIVThe discharge location is within the activeentrance shoal. The associated movement ofsand in this area presents a greater risk ofsand ingress into the discharge infrastructure,and scour as a result of flooding. Continuousrelease discharge infrastructure will maintaina positive flow reducing opportunity for sandingress. Anchoring to the revetment wallreduces flood scour risks.Pipeline route distances to the lower estuary discharge sites are likely to be considerableshorter than those to the wetland/forest. Route selection should occur where possible tominimise social and or environmental impacts to cultural heritage, noise, air quality, traffic,relocation of existing services, surface and groundwater quality, vegetation, etc.The revetment wall discharge site was selected to provide an alternative to the Entrancedischarge site which presented significant construction risks. No assessment ofgeotechnical conditions or stability/structural capacity of the breakwaters for the purposes ofpipeline construction were made as part of this study and remain a construction risk.Discharge infrastructure in the lowerestuary will be subject to marine growth.Design of the ebb-tide release outlets willneed to be cognisant of these risks.Similarly maintenance programs will needto account for the potential effects offouling. Failure risks (e.g. valves failing toclose) and associated impacts, such assand or saltwater ingress are increased forebb-tide release infrastructure which hasrest periods.It is likely that the discharge infrastructurewill contain metal components which willbe subject to erosion in saltwater. There isan increased risk of saltwater intrusion upthe discharge pipeline for ebb-tide release.Discharge infrastructure in the lower estuarywill be subject to marine growth.Maintenance programs will need to accountfor the potential effects of fouling (i.e. reducedcapacity to discharge flow).It is likely that the discharge infrastructure willcontain metal components which will besubject to erosion in saltwater. There is areduced risk of saltwater intrusion up thedischarge pipeline for continuous releasesdue to maintenance of positive dischargeflows.Minor increases in nutrient concentrations have been predicted throughout the estuary forebb-tide and continuous release discharge scenarios thereby increasing the risk of abiological or ecosystem response, e.g. changes in macroinvertebrate communityabundance and distribution, increased algal production and associated risk of algal blooms,changes in trophic status of estuary, etc. These outcomes if realised could impact onidentified nature conservation values and have longer term cumulative impacts on theestuary to support certain fish and bird populations. Determination of actual biological /ecosystem response was beyond the scope of this study and would need to be addressedas part of any future detailed assessment of a discharge in this location.As for Nature Conservation Values, impacts to the health of the estuary and its ability tosupport wildlife and harvest seafoods may increase the risk of impacting on cultural valuesassociated with the estuary. Further assessment of biological / ecosystem responsesassociated with the discharge are required.No impactThis discharge increases the risk of discharges being noticeable to the public either throughthe presence of surface ripples, or via differences in water clarity/hue in the immediatevicinity of the discharge. These effects if noticeable would only be noticeable under certainconditions.As for fishing and swimming above, there may be some perceptions of declining fish healthor catch or unsafe swimming conditions. Further assessment of potential impacts ofdischarges on recreational primary and secondary contact, and consumption of cookedaquatic food water quality standards would be recommended, as has a more detaileddetermination of potential biological/ecosystem responses. It is possible that theseperceptions could be addressed through monitoring and public consultation.Reductions in an individual’s perceived ability to recreate within the estuary may impact onthe tourism potential of the estuary, increasing the risk of socio-economic impacts. TheG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYAspect Region / Value / Element ObjectiveFlood mitigation valuesdischarge within thesurroundingcommunityMaintain role ofEvans River estuaryfor mitigation of floodimpacts from theRichmond RiverWetland / Forest DischargeWetland / Forest Discharge(Tuckombil Canal)(Brandy Arm)The potential for the wetland scheme to cause groundwater quality impacts has not been fullyassessed.No impact No impact No impactRevetment Ebb-Tide DischargeRevetment Continuous DischargeXXXVrisks of impact in this respect are increased in the lower estuary as this is where themajority of fishing, swimming and passive recreation, etc is undertaken (immediatelyadjacent to Evans Head). Perceived impacts associated with fishing, swimming, dischargevisibility and potentially smell all increase the risk of socio-economic impact. Furtherassessments are required to better define if actual impacts would be experienced.LegendPotentially significant or unacceptable impact or riskSlight negative impact or riskNeutral impact or riskBeneficial impactG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXXVIConclusionsThe scenario modelling predicted that both the continuous and ebb-tide release options would resultin increases in total nutrient concentrations throughout the estuary (nitrogen more than phosphorus)and at the beach location outside of the estuary. This outcome is a function of tidal movementswhich move treated effluent throughout the estuary. The choice of ebb-tide discharges generallyresults in improved water quality outcomes (i.e. lower TN concentrations) as much of the effluent isconveyed out to the ocean and does not return. However, on certain tides, i.e. neap tides where lowtidal velocities exist, ebb-tide discharges can result in effluent being retained in the estuary orreturned to the estuary from the ocean on the next flooding tide.The movement of effluent throughout the estuary means that circumstances could arise where thedischarge results in modelled concentrations exceeding the guideline trigger values. This is to saythat prior to the discharge, a site may have had ambient water quality conditions below the guidelinetrigger value; however, with the introduction of the effluent, the pollutant concentrations increase andthen exceed the guideline trigger value. This was not noted to occur at any site within the estuary forthe assessments completed as part of this study, although the assessments were focused on oneyear, i.e. 2008.The modelling showed that the magnitude of the increase in total nutrient concentrations variedthroughout the estuary in response to the location of the ebb-tide and continuous discharge. All ebbtideand continuous release options were to the lower estuary, correspondingly the greatest modelledincreases in nutrients occurred in this location. However, better (i.e. lower) ambient nutrientconcentrations and increased tidal exchange in the lower estuary mitigates the impacts of thedischarge. The estuary in this zone is able to assimilate nutrients without exceeding the guidelinetrigger values.Modelling indicates that ebb-tide and continuous releases in the lower estuary results in increasednutrient concentrations in the upper estuary. The magnitude of the increase is less than thatobserved in the lower estuary as less effluent gets conveyed to the upper estuary by tidal exchange.Using the ANZECC guideline trigger values as the benchmark for scheme acceptability, thencontinuous and ebb-tide release options to the lower estuary may present an unacceptable risk toestuarine water quality by increasing the risk of an adverse biological response, e.g. algal blooms.However, given that the magnitude of the increases in total nutrients is small (i.e. is typically less than5% above background ambient levels in the upper estuary), further water quality and ecologicalassessments could be employed to quantify these risks should these options be further considered.Outside of the estuary, modelled data were extracted from a beach location. Incremental increasesof up to 0.014 mg/L TN and 0.001 mg/L TP were determined for this location. Due to the limitation ofnot having sufficient background water quality data for the beach location, it has not been possible todetermine the total modelled concentrations of TN or TP at this location sufficient to allow comparisonto ANZECC guideline trigger values.The findings of the assessment completed for the wetland / forest discharge scenarios identified thatthe implementation of the wetland / forest leads to increased in evapo-transpiration (ET) rates (i.e. therate at which water is taken up by evaporation and transpiration). This occurred as a result of theG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXXVIIforest having a constant water supply. This effect increased soil moisture deficits (i.e. amount ofrainfall that could be stored prior to runoff) and consequently reduced the volume and frequency ofrunoff events to the estuary. Reductions in volume of runoff events reduce the load of nutrientsdelivered to the estuary, compared to a similar forested area on the same soil profile.Consequently, modelling indicated that were some potential reductions in ambient TN concentrationsin the far upper estuary as a result of the implementation of the Tuckombil Canal wetland / forestoption for treatment and disposal of STP effluent. Full water quality modelling using calibratedcatchment loads and flows is required to refine estimates of the magnitude of the reductions.The outcomes of the impact risk assessment were that the wetland / forest discharge schemes wouldbe likely to present neutral or slight beneficial water quality outcomes within the upper estuary in thecase of the Brandy Arm Creek site, or potentially beneficial outcomes in the case of the TuckombilCanal site, reducing risks associated with adverse biological responses (which were previously notedfor the ebb-tide and continuous release schemes). However, these schemes presented some risksof slightly negative impacts associated with adverse public perceptions of reduced ability to, orenjoyment in recreational activities such as swimming and fishing as a result of a discharge of treatedand polished STP effluent to the estuary. It may be possible to reduce these potential negative risksthrough further assessment and community consultation to address residual community concerns.There are also some unknown factors associated with the wetland / forest site associated with thepotential connectivity of shallow groundwater beneath the forest site and the Evans River estuary andimpact the impact of irrigation on long-term groundwater elevations. Potential impacts of treated andpolished wetland discharges on groundwater quality have also not been assessed. These factorswould be required to be assessed in a more detailed investigation of an actual wetland / forest site.The ebb-tide or continuous discharges from the revetment wall presents a larger number of potentialnegative impact risks. Many of these could be eliminated or improved through further assessment,engineering and design innovation and community consultation and education. Aspects identified aspresenting significant or unacceptable impact risks (in addition to water quality risks discussed above)include:• Commercial fishing craft egress - Based on current information available for minimum tidelevels, bed depths and the drafts of boats which may use the entrance channel for egress to andfrom the ocean, the height of the discharge infrastructure does not provide sufficient freeboard toeliminate risk of contact. The use of appropriate channel markers may lessen this risk to a moreacceptable level.There is a degree of uncertainty of the range of estuary bed depths that may be present at thislocation and the maximum depth to which the discharge infrastructure can be lowered to reducecontact risks. This has been recommended for further investigation.• Passive recreation - The discharge of STP effluent may create a visual difference between thedischarge and the ambient water due to differences in water clarity. Density differences betweenthe effluent water and estuary water will result in effluent rising to the surface leading to thepresence of surface ripples part of the time (most notable for continuous releases). Furthermore,the smell of treated and disinfected effluent when discharged to the estuary may be noticeable toan individual as the discharge plumes surfaces.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXXVIIIThere are uncertainties as to the extent of rippling that may occur (and potentially this may bemitigated through design innovation). There is also uncertainty as to whether the smell of thehighly treated and disinfected effluent will be noticeable as the plume surfaces. Furtherassessment of this potential impact would be required.• Socio-economic values - Reductions in an individual’s perceived ability to recreate within theestuary may impact on the tourism potential of the estuary, increasing the risk of socio-economicimpacts. The risks of impact in this respect are increased in the lower estuary as this is wherethe majority of fishing, swimming and passive recreation, etc is undertaken (i.e. immediatelyadjacent to Evans Head). Perceived impacts associated with fishing, swimming, dischargevisibility and potentially smell all increase the risk of socio-economic impact.RecommendationsThe STP wetland / forest schemes are recommended as the first priority for further investigation.Overall the receiving water quality modelling and associated impact risk assessments identify that thewetland /forest discharge schemes provide a lower social and environmental risk option than therevetment wall ebb-tide or continuous release, subject to further detailed site investigation of theactual wetland / forest site. Initial assessments completed as part of this study recommend a wetland/ forest in the vicinity of the Tuckombil Canal rather than one in the vicinity of Brandy Arm Creek dueto potentially greater receiving water benefits in the Evans River estuary.The revetment wall discharge is recommended as the second priority for further investigation.Although not assessed as part of this study, if costs (or land availability, etc) prove prohibitive for awetland / forest scheme, then a revetment wall discharge would form a second preference. However,this scheme has been identified to present a number of social and environmental risks which withfurther assessment, design and community consultation have the potential to be eliminated orovercome.The adoption of a continuous release arrangement may reduce some operational risks (e.g. sandingress into the discharge infrastructure), but was found to contribute slightly higher total nutrientconcentrations in the upper estuary; the location most at risk of experiencing an adverse biologicalresponse as a result. Hence, it is difficult with the information presently available to recommend aparticular discharge strategy over another. It is recommended that as part of any future more detailedassessment (see below) that both discharge strategies be assessed. If it is determined that thepotential for a biological response is insignificant then a continuous release would be recommendedover an ebb-tide release for its potential operational benefits. A continuous release scheme may alsoprovide for cost savings by avoiding the need for additional transfer infrastructure from the STP to theestuary.The revetment wall site is favoured over other release sites at the Elm St Bridge and Entrance. TheElm St Bridge site has the shallowest bed structure and as such is likely to present the greatest risksfor human interaction with the discharge infrastructure and plume. The Entrance site is considered topresent the most challenging construction option, with the discharge infrastructure to be laid in thelocation of a mobile sand bed. Furthermore, the discharge infrastructure may provide a significantboat navigation hazard.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EXECUTIVE SUMMARYXXXIXFurther AssessmentsAny scheme adopted by Council would need to go through a further round of detailed conceptdevelopment, assessment and costing. At this stage, the scheme could be compared equitably withother schemes already progressed by Council for management of effluent from the Evans Head STPinto the future.Future assessments (potentially forming part of the approval process) that may be required for anyestuarine discharge are detailed below:• Full water quality modelling is required to simulate actual pollutant concentrations, rather thanconservative tracers as was undertaken for this study. The full water quality modelling wouldutilise the HD and AD model information already developed and then add an additional layer ofinformation on key processes (i.e. settling, decay, uptake, etc). This model would also be able tosimulate a range of nutrient species, water clarity, dissolved oxygen, faecal coliforms andchlorophyll-a, etc. In addition to allowing for comparisons of predicted receiving water quality withapplicable water quality objectives (i.e. protection of aquatic ecosystems, primary and secondarycontact recreation, etc), this model could also be used to ascertain potential ecosystem /biological responses associated with the discharge options.Further data collection to support the development and calibration of this model will be required.This will include calibration of flow and load predictions of the WaterCAST catchment model.Additional water quality and sediment quality / benthic flux information may also need to becollected to support the model calibration and validation. In particular better information on algalconcentrations in the estuary will be required, as will as a better definition of the quality ofoverflows from the Richmond River/Rocky Mouth Creek to the Evans River.In respect of the wetland site, the following future assessment would be required:• Further assessment of potential wetland sites would be required to establish their feasibility foruse. At present, key unknowns include the connectivity between shallow groundwater beneaththe forest site and the Evans River; the impact of irrigation on the long-term groundwaterelevation at the sites; and potential groundwater quality impacts of the irrigation of treated andpolished effluent from the wetland to the forest.In respect of the ebb-tide and continuous release, the following future assessments would berequired:• Further assessment of the range of estuary bed movement will be required to determine themaximum depths at which discharge infrastructure could be placed and hence determine theassociated risk of contact with vessels. Further discussion with regulatory authorities such asNSW Maritime will also be essential in determining feasibility and mitigation strategies which maybe appropriate; and• Odour assessments, assessments of plume evolution to the surface and the associated odourrisk this presents need to be assessed to determine if this potential risk would be realised.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

INTRODUCTION 1-11 INTRODUCTIONThis report outlines BMT WBM’s investigations into potential environmental and social impact risksassociated with the discharge of treated effluent from the Evans Head Sewage Treatment Plant(STP) to the Evans River. The study has been designed to address questions posed by RichmondValley Council (‘Council’) which included identification of:• The ability of the Evans River estuary to accept and assimilate or dissipate STP effluentdischarges; and• The impact of STP discharges on the environmental and social values of the Evans Riversystem.At present, treated effluent from the STP discharges to Salty Lagoon, however, the longevity of thiscurrent effluent disposal scheme is limited due to State agency concerns. Outcomes from this studywill provide further input to Council’s deliberations in respect of management of effluent from theEvans Head STP into the future.This report has assessed a number of discharge scenarios, including:• Ebb-tide release scenarios;• Continuous release scenarios; and• Wetland and carbon sequestration forest polishing release scenarios.Assessments have focused on the ultimate (i.e. 2050 flows) from the STP at Evans Head. Effluentdischarge quality for the assessments was based on current (i.e. June 2008 to January 2010)discharge quality recorded by Council at the plant. To this end, a time-series of STP discharges andquality has been used in the various assessments performed (see also report included in AppendixB).To enable assessment of the estuarine discharges, BMT WBM has for this project developed linkedhydrodynamic (HD) and advection/dispersion (AD) models using the RMA suite of modelling tools.These models were used to assess the relative contributions of key pollutants from the variousdischarge scenarios to the estuary. The models allow for interrogation of results at practically anylocation within and immediately offshore from the estuary.The thorough development of the models required BMT WBM to obtain a variety of field dataincluding tidal velocities, flows and salinity datasets at a number of sites in the estuary. Both the HDand AD models were calibrated against the field datasets and validated against informationpreviously collected and compiled by others.Potential discharge sites for all options were established in consultation with Council. With the initialdischarge sites identified, release options were developed. This enabled BMT WBM to complete‘near field’ modelling of the discharges using the CORMIX model to provide a first pass assessmentof likely dilution characteristics of the proposed discharges. The results from this ‘near field’modelling were used to inform the ‘far field’ (i.e. HD and AD) to allow them to more accurately modelplume / pollutant evolution through the estuary.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

INTRODUCTION 1-2For the wetland / carbon sequestration forest polishing option, BMT WBM re-established and refinedprevious modelling completed for this option as originally developed by the Wetland and CarbonGroup (2009). The purpose of this modelling was to convert the STP discharges defined byHydrosphere (2010) into an ultimate release scenario for the wetland and forest system, such that theeffects of the release could be assessed using the previously established HD and AD models.Subsequent to the scenario runs being completed, the models were interrogated and theconcentrations of key pollutant species (total nitrogen and total phosphorus) contributed by scenariosat points of interest (established in consultation with Council) were extracted from the model. Theadditional concentrations of pollutants as predicted by the models could then be compared toapplicable water quality objectives (WQOs) at that location. Comparisons to WQOs (which arethemselves cognisant of the various social and environmental values associated with estuary)provides a measure of the risk presented by the scheme to water quality and associated ecosystem /biological factors.Furthermore, an impact risk assessment was undertaken to compare the performance of selecteddischarge schemes against a set of objectives derived for existing identified estuarine values andother construction and operability factors.A preferred scenario could, subsequent to this study, be progressed by Council to detailed conceptdesign stage to allow for further environmental and social impact assessment studies to becompleted, with associated costs completed. This would allow for the preferred scenario to becompared with other potentially viable options, which is essential for any future stakeholderconsultation.This report has been laid out in the following sections:• Section 2 – Data Collection and Review – Discusses key datasets collected for use in thestudy, either by direct measurement or obtained from previous studies or third parties;• Section 3 – Review of Estuary Processes – Review key estuarine processes which influencewater quality within the estuary;• Section 4 – Catchment Modelling – Overview of catchment model establishment and review ofrelevant model outputs;• Section 5 – Wetland / Forest Modelling – Review of existing wetland and carbon sequestrationstudies and development of models to assess the performance of these systems;• Section 6 – Hydrodynamic and Advection/Dispersion Modelling – Discusses theestablishment, calibration and validation of these key modelling elements;• Section 7 – Scenario Assessment – Assesses various release scenarios, including continuous,ebb-tide and wetland / forest based discharges for their potential water quality impacts.• Section 8 – Impact Risk Assessment – Provides further discussion in respect of the modellingoutcomes and water quality effects, and related potential impacts on social and otherenvironmental values. Further definition of discharge arrangements are provided along with areview of potential site constraints that may be applicable in the design and construction of thedischarge; andG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

INTRODUCTION 1-3• Section 9 – Conclusions and Recommendations – Recommendations are provided forconsideration by Council in respect of the assessments performed as part of this investigation.1.1 BackgroundIn 1995, Council and the Department of Land and Water Conservation (now Department ofEnvironment, Climate Change and Water, DECCW) recognised the need to investigate strategies toimprove the Woodburn-Evans Head wastewater system. This was due to a number of factorsincluding:• The release of effluent to Salty Lagoon is no longer regarded as an acceptable long-termsolution by the Department of Environment, Climate Change and Water (DECCW);• The old STP was not meeting licensed water quality targets; and• Future population projections indicate that the capacity of the existing system was likely to beexceeded due to population growth.Investigations into necessary upgrade components commenced in 1996. In order to address theSTP capacity and effluent quality targets, the STP has been replaced with a new 5,500 EP (Stage 1)Intermittently Decanted Extended Aeration (IDEA) reactor with chemical dosing and disinfection. Thisplant came on-line in August 2007. Stage 2 (11,000 EP) will be completed to provide for futuregrowth in sewage flows.Associated with the plant upgrades a number of effluent management strategies have beeninvestigated which can be divided into two broad categories:• Reuse; and• Disposal (discharge of excess treated effluent).Council has identified various effluent disposal and/or reuse options to divert STP discharges fromSalty Lagoon. Options which are currently considered to be potentially viable include:• Dry weather open space irrigation in Evans Head and Woodburn;• Deep well injection;• Wetland and carbon sequestration forest with wet weather discharge to Evans River (focus ofthis investigation); and• Discharge to Evans River (focus of this investigation).There are significant cost implications for all potential discharge options (reviewing scheme costswere not a requirement for this study). Environmental and social considerations have also beenidentified as significant factors in the selection of the preferred option.In consultation with DECCW, Council has determined that:1. Effluent reuse opportunities will be considered in parallel with the discharge of wet weather flowsand will depend on the location of effluent transfer system infrastructure;G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

INTRODUCTION 1-42. Deep well injection is a potentially feasible option, however, further investigation will requireclogging/injection trials to confirm feasibility and design parameters. Due to the cost and timeframe required for these trials, other options are being investigated at this time; and3. There was a lack of knowledge of the Evans River flow regime and the potential for the estuaryto assimilate STP discharges. To enable comparison of the options involving discharge to theEvans River with other potential options, hydrodynamic and water quality modelling of the EvansRiver system was required.The item identified in dot point three (3) formed the basis of this investigation. In particular, Council’scurrent Evans Head STP licence with DECCW identifies Pollution Reduction Program (PRP) 6 whichis restated below,“To assist in considering the feasibility of effluent disposal locations, the Licensee mustundertake hydrodynamic and water quality modelling of the Evans River system. Theassessment needs to address the proposed locations for effluent discharge. A reportshould be prepared and submitted to DECCW.”This report will fulfil the PRP requirements outlined in the Evans Head STP Licence with DECCW.1.2 Location and Overview of the Evans RiverThe Evans River is situated in the Northern Rivers region of NSW (see Figure 1-1). It isapproximately 200km south of Brisbane (direct) and 530km NNE of Sydney (direct). The 2006census recorded a population of 2,600 permanent residents. Generally residents of the township areof an older demographic with populations of persons below 54 being below the NSW state averageand above for persons in excess of 54 years of age. This is consistent with a large number of retireeswho live within Evans Head. During holiday periods the total population of the township increasessignificantly. While Evans Head is the principal settlement in the catchment, there are a number ofrural residential allotments in the Doonbah locality. Woodburn resides at the upper end of thecatchment, although most parts of Woodburn drain towards the Richmond River and not into theEvans River.The catchment of the Evans River is approximately 92 km 2 (excluding water areas) and is mostly(75%) comprised of forested areas. Grazing in the upper reaches occupies a further 11% of thecatchment, with other forms of agriculture, intensive use, urban and rural residential lands, etccomprising 14% of the catchment.The Evans River itself commences at Tuckombil Weir, some 16km from the mouth of the estuary.The estuary is tidal for its full length and has a number of minor tributaries, such as Brandy ArmCreek. The Evans River joins the ocean at Evans Head, where twin breakwaters were constructed inthe 1960’s to aid boating navigation into and out of the estuary. Currently there are believed to be noactive oystering or commercial fishing within the estuary, although it is popular for a variety ofrecreational pursuits including fishing, boating, swimming, etc.The Evans River is separated by the Tuckombil weir at its upstream end from the Richmond River(and Rocky Mouth Creek). During flood events, the Tuckombil weir may overtop introducing floodwaters into the Tuckombil Canal as the top end of the estuary. The Evans Head STP dischargestreated sewage to Salty Lagoon to the north of Evans Head (outside of the Evans River catchment).G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

INTRODUCTION 1-61.2.1 Rainfall and ClimateData obtained from the Bureau of Meteorology (BoM) was analysed and average annual rainfall atEvans Head (RAAF Bombing Range) was 1,387 mm/yr over the period of 1/1/1999 to 31/12/2008(~4% of rainfall data entries were missing). At the upper end of the catchment, average rainfall atWoodburn over the period of 1/1/1886 to 31/12/2006 was 1,351 mm/year.Rainfall averages at Woodburn and Evans Head over a consistent period from 1999 to 2009 were1,311 mm/year and 1,422 mm/year, respectively.Figure 1-2 shows a plot of annual average rainfall at Evans Head and Woodburn over the period of1/1/1999 to 31/12/2006. Generally, it can be seen that the two localities have a similar pattern ofrainfall and that annual average rainfall at Woodburn is around 100 mm less than that at Evans Head.Figure 1-2 also shows other selected climate data including average monthly rainfall, temperatureand wind speed. Further information on climate including potential evapo-transpiration and winddirection are included in Sections 4.2.3 and 2.4, respectively.Rainfall Comparisons Evans River Catchment 1999 to 2009Average Monthly Rainfall Evans Head 1998 to 200825002502000Woodburn RainfallEvans Head Rainfall200Rain mmRainfall Totals (mm)15001000Rainfall Totals (mm)1501005005001999 2000 2001 2002 2003 2004 2005 2006 2007 2008 200930YearAverage Monthly Temperatures Evans Head 1998 to 200804Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMonthAverage Monthly Wind Speed Evans Head 2003 to 2008253.5Temperature o C2015105Max TMin TMean TAverage Wind Speed (m/s)32.521.510.5Wind m/s00Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecMonthYearFigure 1-2 Rainfall, Wind and Temperature Data for Evans Head (Varying Periods)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-12 DATA COLLECTION AND REVIEWThis section overviews field-data collection activities undertaken by BMT WBM, as well as thecollection, collation and review of data from third-parties. Commentary is provided on the suitability ofthe data for use in model development, calibration and validation.2.1 Field DataField data collection has been undertaken to provide tidal current, tidal depth, conductivity,temperature and turbidity data. Field data collection was commenced on 31 st January 2010 andconcluded on the 19 th February 2010.Further detailed description of data collection activities is provided in the following sections.2.1.1 Tidal FlowTidal flows were recorded using an Acoustic Doppler Current Profiler (ADCP). This instrumenttransmits bursts of sound at a known frequency into the water column. The sound is scattered byplankton-sized particles (reflectors) carried by the water currents and some is received back by theADCP, which listens for echoes. As echoes are received from deeper in the water column, the ADCPassigns different water depths (depth cells) to corresponding parts of the echo record. This enablesthe ADCP to define vertical profiles of the current velocity. The motion of the reflectors relative to theADCP causes the echo to change frequency by an amount proportional to their velocity. The ADCPmeasures this frequency change i.e. ‘Doppler shift’ and thus constructs vertical current profiles fromthe echoes returned below the vessel track. Using the bottom-track function of the instrument,discharge can be calculated from the measured velocities across the channel.The ADCP instrument used was a RD Instruments 1200 kHz Broadband ADCP. This instrument wasmounted on a 5.5m aluminium hulled commercial survey vessel owned by BMT WBM which isregularly used for such fieldwork (refer Figure 2-6).Two transect locations were selected as shown in Figure 2-1. Locations for cross-sections werepreferentially chosen in areas with clearly defined river banks in order to account for the river flow asaccurately as possible (i.e. avoid significant tidal flow losses in shallow areas not traversable by aboat). Measurements were recorded over a full tidal cycle for over 13 hours at 15 minute intervals.Tidal flow measurements have been collected on one spring (two transects) and one neap tide (onetransect). Based on the outcomes of the neap tide recordings at the far downstream end of theEvans River, the upstream neap tide recording was abandoned due to the expected low tidalvelocities. Such low tidal velocities would have been difficult to record as the limit of accuracy for theADCP is around ±0.1 m/s.The data collected along these transects is presented in Figure 2-3, Figure 2-4 and Figure 2-5 assummary current flow and velocity speed and direction. It is noted that the downstream spring tidedataset presents a clearer tidal signal than the other two datasets, principally due to the lowermagnitude of the current in the upstream section during spring tide conditions, and in the downstreamsection during neap tide conditions.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-3Figure 2-2ADCP and GPS Instrumentation aboard VesselFlow (m3/s)15050-50-150Current Speed (m/s)0.80.60.40.20Current Direction (Degree)3603002401801206002/02/201010:002/02/201011:002/02/201012:002/02/201013:002/02/201014:002/02/201015:002/02/201016:002/02/201017:002/02/201018:002/02/201019:002/02/201020:002/02/201021:002/02/201022:002/02/201023:003/02/20100:003/02/20101:00Figure 2-3 Downstream Transect – Spring Tide (2 February 2010)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-4150Flow (m3/s)50-50-150Current Speed (m/s)0.80.60.40.20Current Direction (Degree)3603002401801206003/02/201012:003/02/201013:003/02/201014:003/02/201015:003/02/201016:003/02/201017:003/02/201018:003/02/201019:003/02/201020:003/02/201021:003/02/201022:003/02/201023:004/02/20100:004/02/20101:004/02/20102:00Figure 2-4 Upstream Transect – Spring Tide (3 February 2010)150Flow (m3/s)50-50-150Current Speed (m/s)0.80.60.40.20Current Direction (Degree)3603002401801206008/02/201010:008/02/201011:008/02/201012:008/02/201013:008/02/201014:008/02/201015:008/02/201016:008/02/201017:008/02/201018:008/02/201019:008/02/201020:008/02/201021:008/02/201022:008/02/201023:009/02/20100:00Figure 2-5 Downstream Transect – Neap Tide (8 February 2010)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-52.1.2 Conductivity, Temperature, Depth (CTD) and TurbidityPre-calibrated loggers measuring conductivity, temperature and depth (CTD) were mounted to fixedstructures below low water datum at three locations along the Evans River, as shown in Figure 2-1.Figure 2-6 shows the structure immediately after retrieval. The fixed recorders measure changes intidal depth (pressure sensing), water temperature and conductivity across a recording period. Anadditional turbidity probe was added to the mounting structure to provide this additional dataset,although the results of the turbidity metering have not been presented as the probe became blockedafter a few days due to sand movement.A CTD logger (plus turbidity probe) was placed near the entrance of the Evans River (~3 weekdeployment), and a depth sensor (i.e. tide recorder) was placed initially in the upper estuary (~4 daydeployment) and then moved to a mid-estuary position for the remainder of the deployment (~2 weekdeployment) as shown in Figure 2-1. The instruments record datasets every 6 minutes.Figure 2-6CTD Instrument and Turbidity Meter on Bottom MountThe recorded datasets are presented in Figure 2-7, Figure 2-8 and Figure 2-9.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-61Tidal Elevation (m)0.50-0.5-1Water Temperature(Degree Celsius)3530252015Electrical Conductivity (uS/cm)60000500004000030000200001000031/01/20100:0031/01/201012:001/02/20100:001/02/201012:002/02/20100:002/02/201012:003/02/20100:003/02/201012:004/02/20100:004/02/201012:00Figure 2-7 CTD Record – Initial Upstream Location (Upstream 1)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-71Tidal Elevation (m)0.50-0.5-1Water Temperature(Degree Celsius)3530252015Electrical Conductivity (uS/cm)6000050000400003000020000100003/02/2010 0:00 5/02/2010 0:00 7/02/2010 0:00 9/02/2010 0:00 11/02/2010 0:00 13/02/2010 0:00 15/02/2010 0:00 17/02/2010 0:00Figure 2-8 CTD Record – Final Upstream Location (Upstream 2)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-81Tidal Elevation (m)0.50-0.5-1Water Temperature(Degree Celsius)3530252015Electrical Conductivity (uS/cm)60000500004000030000200001000031/01/20100:002/02/20100:004/02/20100:006/02/20100:008/02/20100:0010/02/20100:0012/02/20100:0014/02/20100:0016/02/20100:0018/02/20100:0020/02/20100:00Figure 2-9CTD Record – Downstream Location (Downstream)In respect of the logger data at site ‘Downstream’ it is noted that:• The tidal elevation record indicates some rough weather patterns during neap tide as denoted bythe increase in line thickness (i.e. wave swell) in Figure 2-9. The ocean roughness was alsoobserved in the field during tidal recordings at this time; and• The electrical conductivity record indicates some issues with the conductivity meter for most ofthe measurement period. This provides no issues to this study, as this data was not ultimatelyrequired for use in model calibration or validation.2.2 Existing ReportsThe following previously completed discharge and release investigation reports have been reviewed:• GHD (2006a) Report for Woodburn Evans Head Wastewater Management Scheme. SaltyLagoon and Ebb-tide Release Investigations – Water Quality (Report 1 of 5), Prepared forRichmond Valley Council, April 2006;• GHD (2006c) Report for Woodburn Evans Head Wastewater Management Scheme. Stage 1Effluent Release investigations, Prepared for Richmond Valley Council, September 2006;• MHL1796 (2007) Evans head Numerical Pollutant Dispersion Study, Manly hydraulicsLaboratory Report #1796, Prepared for Connell Wagner, December 2007;G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-9• Connell Wagner (2008) Final Report Woodburn Evans Head Wastewater Management Scheme:Stage 2 Release Investigation, Report #28268, Prepared for Richmond Valley Council, June2008;• Hydrosphere (2008) Evans Head STP Effluent Management Peer Review of Reuse and ReleaseOptions, Prepared for Richmond Valley Council; and• Aurecon (2009) Addendum: Offshore Pipeline and Diffuser Engineering Considerations.Woodburn Evans Head Wastewater Management Scheme: Stage 2 Release Investigations.Prepared for Richmond Valley Council, April 2009.Most of these previous studies have focused on ebb-tide releases in the vicinity of the mouth of theestuary and at deep ocean sites up to 800m north east of the estuary mouth. The Aureconaddendum to the Wastewater Management Scheme includes an offshore discharge location 2.3 kmnortheast of the estuary mouth.These studies utilise information from an initial release investigation study (GHD, 2006a) whichdefined the flushing characteristics of the estuary as being poor, based on a MIKE11 stationarycurrent assessment. In BMT WBM’s experience, such assessments are usually difficult to interpretand it is believed that a more accurate, dynamic hydrodynamic assessment of the estuary isnecessary to properly understand estuarine responses to tidal flushing and accordingly to assesspotential discharge sites within the estuary. Furthermore, earlier studies had very limited waterquality data available to them, which limited the conclusions which could be reached in these studies.Council has, since 2006, collected a large quantity of water quality data in the Evans River.Hence, it has been deemed that most of the material developed and/or used for the previousinvestigations was of limited use for the current study.A variety of other studies have been of use in defining physical conditions within the estuary andthese are referred to throughout the report.2.3 MHL DataPrevious study material includes Manly Hydraulics Laboratory (MHL) reconstituted tidal levels atEvans Head, Iron Gates and Tuckombil Floodgates for the periods 1/1/2005 to 2/1/2008 and1/1/1996 to 2/1/1998. It is noted that these data are reconstituted rather than recorded data. Furtherdata was provided by MHL for use in the current study. These data are presented in detail in thefollowing sections.2.3.1 Estuary Tide Heights2.3.1.1 Fixed RecordersTidal level data at three fixed monitoring stations within the Evans River and Rocky Mouth Creekwere purchased from MHL as follows:• Iron Gates Site: 15-minute data from August 1997 to March 2010;• Evans River Fishing Co-op Site: 15-minute data from July 1997 to March 2010;• Rocky Mouth Creek Site: 15 minute data from September 2004 to March 2010;G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-10• Tuckombil Floodgates: 15 minute data from 1990 to March 2010; and• Tuckombil Weir at Pacific Highway: 15 minute data 1989 to March 2010.A selection of this data at Iron Gates and Fishing Co-op Sites are presented in Figure 2-10 for theperiod November 2005 to February 2006. Refer to Figure 2-12 for the location of the five permanentmonitoring sites.It is noted that the Fishing Co-op data presents a gap for the first week of December 2005. It isbelieved that this will not be an issue as these datasets have been used for model validationpurposes (rather than calibration).Figure 2-10 Tidal Levels – Evans River Iron Gates and Fishing Co-op Sites2.3.1.2 Temporary RecordersFurther tidal level data were provided by MHL from the DNR Evans River Tidal Data Collection Study(MHL, 2006), as follows:• Site 2: 15-minute data from November 2005 to March 2006;• Site 5: 15-minute data from November 2005 to March 2006;• Site 7: 15-minute data from November 2005 to December 2005;• Site 9: 15-minute data from December 2005 to February 2006; and• Site 11: 15-minute data from November 2005 to March 2006.These data are presented in Figure 2-11. Refer to Figure 2-12 and/or MHL (2006) for the locations ofthese temporary monitoring sites.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-11As can be seen in Figure 2-11, data recorded at Site 7 will be of limited use in this study due to theshort time span compared to other datasets (approximately one month only). Data recorded at allother sites will be suitable for the hydrodynamic model validation.Figure 2-11 Tidal Levels – Evans River Temporary SitesG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-132.3.2 Tidal Velocity and FlowTidal velocity and flow data recorded as part of the DNR Evans River Tidal Data Collection Study(MHL, 2006) were provided for use in this study. These data are presented in Figure 2-13 andconsists of ADCP velocity and flow measurements taken over a complete flood and ebb-tide cycle ata single location within the Evans River entrance (‘Site 3’). Refer to Figure 2-1 for the exact locationof Site 3. These data are suitable for use in the hydrodynamic model validation process.Flow (m3/s)25015050-50-150-250Current Speed (m/s)10.80.60.40.20Current Direction (Degree)3603002401801206002/03/20063:002/03/20064:002/03/20065:002/03/20066:00Tidal Flood Period2/03/20067:002/03/20068:002/03/20069:002/03/200610:002/03/200611:002/03/200612:002/03/200613:00Tidal Ebb Period2/03/200614:002/03/200615:002/03/200616:002/03/200617:002/03/200618:00Figure 2-13 Evans River Entrance Transect (Site 3) – 2 March 20062.3.3 Ocean Tide HeightsOcean level data was purchased from MHL at two different locations north and south of the EvansRiver mouth, as follows:• Ballina: 15-minute data from January 1997 to June 2009; and• Yamba: 15-minute data from January 1997 to June 2009.These data are presented in Figure 2-15 over the period November 2005 to February 2006. Thelocation of MHL ocean tidal recorders is shown in Figure 2-14.These datasets will be used to generate downstream boundary conditions for the Evans Riverhydrodynamic model.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-152.4 BoM DataFigure 2-15 Ocean Level DataPrevious studies have used climatic data from the Bureau of Meteorology (BoM) station at BallinaAirport. However, it is believed that the local Evans Head station might be more relevant for thecurrent study. As such, climatic data was requested from the BoM at the Evans Head RAAFBombing Range Station (#058212) for the period April 1998 onwards providing:• Hourly rainfall;• Hourly wind speed and direction;• Hourly air temperature; and• Hourly relative humidity.Location of the Evans Head station is shown in Figure 2-14. Figure 2-16 provides a snapshot ofthese data over the period November 2005 to February 2010. It is noted that two significant datagaps have been identified within this period and are highlighted in red in this figure. The periodsselected for modelling purposes will be considered outside these gaps if possible. If this is notpossible, assumptions will be made in order to fill in those gaps with appropriate data (e.g. from asimilar period in a different year, or from the Ballina BoM weather data if available).Detailed statistics over this period are provided in Table 2-1. Key elements are as follows:• A maximum wind speed of 20 m/s was observed, with an average value of about 5m/s acrossthe entire period considered; and• The average wind direction is about 200 degrees. This indicates prevailing southerly to southwesterlywinds.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-16Table 2-1 BoM Data Statistics (November 2005 – February 2010)Rainfall Air Temp. Rel. Humidity Wind Speed Wind Dir.mm ºC % m/s º from NorthMinimum 0.0 4.0 9 0.0 0Maximum 153.2 38.7 100 20.0 360Average 2.1 19.2 76 4.6 19620th Percentile 0.0 15.1 60 3.1 9050th Percentile 0.0 19.3 77 4.2 20080th Percentile 0.6 23.0 97 6.1 320150Rainfall (mm)100500No Data - 23/1/2006 to 3/2/2010 No Data - 5/12/2006 to 19/12/2010Air Temperature(Degree Celsius)403020100Relative Humidity (%)10080604020035030025020015010050001/11/0531/12/0501/03/0630/04/0629/06/0628/08/0627/10/0626/12/0624/02/0725/04/0724/06/0723/08/0722/10/0721/12/0719/02/0819/04/0818/06/0817/08/0816/10/0815/12/0813/02/0914/04/0913/06/0912/08/0911/10/0910/12/0908/02/10Wind Speed (m/s)20151050Wind Direction(Degree coming from)Figure 2-16Evans Head RAAF Weather Station Data Sample2.5 Bathymetric DataThe following bathymetric data were sourced by BMT WBM:• 1997 DLWC hydrographic survey data outside of the Evans River entrance (i.e. coastal area);and• 2006 DECC hydrographic survey of the Evans River Estuary.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-17No details of the survey accuracy were provided.Both datasets were aligned to the same datum (i.e. Australian Height Datum) by subtracting 0.63mfrom the 1997 DLWC ocean bathymetric data, which was initially provided in low water ordinaryspring tide datum reference. The Evans Head mean low water springs (MLWS) level used in thisconversion, and is based on Wainwright (1997).The data was then used to generate a Digital Elevation Model (DEM) of the area. This DEM was alsocompleted in the offshore area using boating chart data from the 1:150,000 Hydrographic mapAUS813. The full DEM is shown in two parts representing the downstream and upstream sections ofthe estuary as shown in Figure 2-17 and Figure 2-18, respectively.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-202.6 Water Quality Data2.6.1 Beachwatch DataCouncil has been in the NSW Beachwatch Partnership Program since October 2006. Councilcommitted to this program for a 5 year period.The NSW Beachwatch Partnership Program is coordinated through the Department of EnvironmentClimate Change and Water (DECCW), who provide assistance with project planning, qualityassurance and community reporting including State of the Beaches Report. The program monitorswater at swimming locations to assess the level of faecal contamination.The program monitors enterococci as the single preferred indicator organism for the detection offaecal contamination in recreational waters (in accordance with National Health and MedicalResearch Council (NHMRC) guidelines). Sampling is undertaken regularly between November andApril at four locations around Evans Heads including Airforce Beach, Main Beach, Shark Bay and inthe Evans River at a place locally known as the Bream Hole. The results are posted on the internetand published in various reports, such as the State of the Beaches report.Prior to May 2009, Beachwatch also tested for the bacterial indicator, faecal coliforms (also known asthermotolerant coliforms). While this bacterial indicator is present in very high numbers in rawsewage, it dies off more rapidly than enterococci in marine waters and has been found to correlatepoorly with illness rates in swimmers.Compliance limits for the testing were originally established as part of the 1990 NHMRC SwimmingWater Quality Guidelines. These were current up until May 2009 when new guidelines were adopted.The 1990 guidelines provided compliance limits of 150 faecal coliforms/100 mL and 35enterococci/100 mL of water. The 2008 guidelines ‘Guidelines for Managing Risks in RecreationalWater’ (NHMRC, 2008), provide a revised methodology for providing beach classifications of whichmonitoring of enterococci levels in water remains a central component.Relevant to these 1990 guidelines, the following results were obtained:• During the 2006/07 monitoring period, all sites achieved a 6 out of 6 (i.e. six pass ratings out ofsix sampling events) for faecal coliforms and enterococci;• During the 2007/08 monitoring period, all sites external to the estuary achieved a 7 out of 7rating, however, the site in the Evans River achieved only a 6 out 7 rating. The test which failedwas observed to be February 2008 which coincides with periods of high local rainfall andpotentially flooding; and• During the 2008/09 monitoring period, all sites external to the estuary achieved a 7 out of 7rating, however, the site in the Evans River achieved only a 6 out 7 rating. The test which failedwas observed to be April 2009 which again correlates to a period of high rainfall.Generally, recorded levels of faecal coliforms and enterococci on the ocean beaches, i.e. AirforceBeach and Main Beach were observed to be responsive to rainfall. This was less evident at SharkBay. While levels in the Evans River were responsive to rainfall, there were occasions during periodsG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-21of dry weather when levels were elevated suggesting the influence of other factors, e.g. leaking septicor sewer systems.Although identified as another source of water quality data, the information compiled by theBeachwatch program is of limited use in this study as the models developed cannot at this stagesimulate the decay of pollutants. Furthermore, during dry weather periods the Evans Head STPdischarges waters would be expected to be low, and there would be expected to be an increase aftera flood event as a result of general catchment runoff.2.6.2 Council and DECCW DataCouncil initiated a monitoring program on the Evans River in August 2006. This program collecteddata over a 29 month period, with a mixture of monthly and fortnightly sampling and concluded inJanuary 2009. The program recorded data from 5 sites (see Figure 2-19) and collected a range ofphysico-chemical data as shown in Table 2-2.DECCW also collected water quality data from the Evans River as part of the State MonitoringEvaluation and Reporting (MER) Process. DECCW collected samples from 2 sites (see Figure 2-19)in the upper estuary and has provided data for a range of physico-chemical data as shown in Table2-2. Both information sets have been extracted from a supporting report included in Appendix A.Additional information has been provided by DECCW during the course of the study, representingdata collected from the Evans River in 2009 and early 2010. In review of this data it was noted thatdifferent site locations were used for the collection of this data and as such this data has not beenutilised in this study.Table 2-2Water Quality Indicator Data Collected by Council and DECCWCouncilpHTurbidityTemperatureDissolved OxygenElectrical ConductivityFaecal ColiformsBiological Oxygen DemandSuspended SolidsTotal NitrogenTotal PhosphorusTotal AluminiumTotal IronDECCWColourTurbidityTemperatureDissolved OxygenElectrical ConductivitySalinitySecchi Disk depthChlorophyll-aTotal NitrogenTotal Dissolved NitrogenTotal PhosphorusTotal Dissolved PhosphorusComparisons of existing water quality data to guideline values is provided later in this section.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-22Figure 2-19 Map of Council and DECCW Sample Sites (Hydrosphere, 2009)2.6.2.1 Water Quality Guidelines and Environmental ValuesHydrosphere (2009) which has been included in Appendix A, provides details of water qualityguidelines that are applicable to the Evans River. These guidelines include trigger values for a rangeof physical, chemical and biological water quality indicators.In general, guideline values are established for various types of waterways (e.g. freshwater,estuarine, marine, etc) to protect Environmental Values (EVs) particular to those systems. EVs areassigned by the community and stakeholders who utilise and manage the system and generallyrepresent aspirational goals for the current and future condition of the waterways.Exceedence of the trigger values can mean that desired EVs may not be achieved, and consequentlythere may exist an increased potential for environmental or social impacts to be realised. Some EVsfor the Evans River were established by DECCW in 1999. Using data provided in the Evans RiverEstuary Management Plan (WBM, 2002) and the water quality and river flow objectives currentlyrecommended by DECCW, the current set of EVs include:• Protection of aquatic ecosystems;• Visual amenity;• Secondary contact recreation;• Primary contact recreation;G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-23• Consumption of aquatic foods (to be cooked prior to eating);• Maintain wetland and floodplain inundation;• Manage groundwater for ecosystems;• Minimise effects of weirs and other structures; and• Maintain or rehabilitate estuarine processes and habitats.ANZECC Trigger ValuesThe Australian and New Zealand Environment and Conservation Council (ANZECC, 2000) guidelinesprovide default trigger values for slightly disturbed ecosystems in south east Australia. These defaulttrigger values are recommended for use where no locally specific guideline values exist and areprovided in Table 2-2 (after Hydrosphere, 2009). The trigger values do not apply to waterways duringperiods of rainfall (causing catchment runoff) or during periods of extreme dry. It is considered thatonly the estuarine values would be applicable to the monitoring carried out by Council and DECCW,as all sites are contained within tidal sections of the river. For analysis of model results in theproximity of the beach, the marine values would apply.Table 2-3Default trigger values for slightly disturbed ecosystems in south-east Australia(Adapted from Tables 3.3.2 and 3.3.3, chapter 3, ANZECC 2000)EcosystemtypeLowland River(< 150 m AHD)Chl-a(µg/L)Turbidity(NTU)TP(mg/L)Sol P(mg/L)TN(mg/L)NOx(mg/L)NH 4(mg/L)DO(%sat)5 6-50 0.05 0.02 0.50 0.04 0.02 85-100% 6.5-8.0Estuaries 4 0.5-10 0.03 0.005 0.30 0.015 0.015 80-110 7.0-8.5Marine 1 na 0.025 0.01 0.12 0.005 0.015 90-110 8.0-8.4pHDECCW (1999) Trigger ValuesLocally specific guideline values do however exist for the Evans River. As indicated earlier in thissection, DECCW have established a set of EVs for the Evans River (as it is part of the RichmondRiver system), associated with these were numerical water quality objectives. Upon review of theseguideline values it was established that the objectives for chlorophyll-a, turbidity, total phosphorus,total nitrogen, dissolved oxygen and pH are the same as established by ANZECC (2000) anddocumented in Table 2-3. No specific values were provided in these guidelines for solublephosphorus, ammonia or nitrogen oxide species (i.e. NOx). Consequently, the ANZECC (2000)values will be applicable.Numerical water quality objectives were documented by DECCW (1999) for visual amenity,secondary contact recreation and primary contact recreation and aquatic foods. Key objectivesinclude:• Secchi disk depth ≥ 1.6m (Primary Contact);•

DATA COLLECTION AND REVIEW 2-24•

DATA COLLECTION AND REVIEW 2-25pH9876543210pHSite 1 Site 2 Site 3 Site 4 Site 5Min OutlierMax OutlierDO (% Saturation)140%120%100%80%60%40%20%0%Dissolved OxygenSite 1 Site 2 Site 3 Site 4 Site 5Min Outlier Max OutlierElectrical Conductivity (µS/cm)700006000050000400003000020000100000Electrical ConductivitySite 1 Site 2 Site 3 Site 4 Site 5Min Outlier Max OutlierTrubidity (NTU)9080706050403020100TurbiditySite 1 Site 2 Site 3 Site 4 Site 5Min OutlierDECCW WQOs ‐ dashed blackANZECC WQOs ‐ solid redMax Outlier35Temperature160Total Suspended Solids16Biological Oxygen Demand3.5Total AluminiumTemperature (ºC)30252015105Total Suspended Solids (mg/L)14012010080604020Biological Oxygen Demand (mg/L))1412108642Total Aluminium (mg/L)32.521.510.50Site 1 Site 2 Site 3 Site 4 Site 5Min OutlierMax Outlier0Site 1 Site 2 Site 3 Site 4 Site 5Min OutlierMax Outlier0Site 1 Site 2 Site 3 Site 4 Site 5Min OutlierMax Outlier0Site 1 Site 2 Site 3 Site 4 Site 5Min OutlierMax Outlier0.4Total Phosphorus3Total Nitrogen9Total Iron2500Faecal ColiformsTotal Phosphorus (mg/L)0.350.30.250.20.150.10.05Total Nitrogen (mg/L)2.521.510.5Total Iron(mg/L)87654321Faecal Coliforms (CFU/100mL)2000150010005000Site 1 Site 2 Site 3 Site 4 Site 5Min Outlier Max Outlier0Site 1 Site 2 Site 3 Site 4 Site 5Min Outlier Max Outlier0Site 1 Site 2 Site 3 Site 4 Site 5Min Outlier Max Outlier0Site 1 Site 2 Site 3 Site 4 Site 5Min Outlier Max OutlierFigure 2-20 Council Water Quality Data (38 samples per site)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-26The box and whisker plots show a box of which the upper bar represents the 75 th percentile value,the middle bar represents the median (i.e. 50 th percentile value) and the lower bar represents the25% percentile value. The whiskers extend for 1.5 times the inter-quartile range (unless maximum orminimum data values lie within this range and they then form the end of the whiskers). If maximum orminimum values lie outside of the range of the whiskers, they are shown on the graph.The median values will tend to represent conditions during periods of dry weather for mostparameters. During periods of wet weather when inflows are entering the Evans River, variousparameters will either increase (such as for nutrients, turbidity, total suspended solids, faecalcoliforms, metals, etc) or decrease (such as electrical conductivity, dissolved oxygen, etc). The 25 thand 75 th percentile values and the whiskers shown on the graphs provide an indication of waterquality responses during periods of wet weather.Additionally, Auslebrook (2008) and Hydrosphere (2009) (included in Appendix A) provide time-seriesrepresentations of the same datasets as well. These datasets demonstrate the impact of wetweather events on water quality within the Evans River.Low flow conditions (i.e. periods of extended dry weather where catchment inputs are limited) allowthe concentrations of some physico-chemical parameters (not relevant for pH, DO, temperature orconductivity) to decrease as a result of extended periods of tidal flushing as well as other forms of instreamprocessing and biological uptake. Generally speaking, during periods of low flow waterquality objectives are achieved at all sites.In reference to Figure 2-20 and the time-series graphs included in Appendix A, the followingcomments are made:• pH trends from near oceanic pH (i.e. median about 8) at the downstream sites, to about 7.3 atthe upstream sites in a roughly linear fashion between sites during periods of dry weather. Theresultant pH in the estuary at various locations is a balance between fluvial and groundwaterdischarges at the upper end of the catchment and oceanic tidal exchange at the lower end.During periods of high rainfall, pH in the system can drop to as low as 5 (minimum 7recommended by ANZECC) as a result of catchment discharges (i.e. drainage from Brandy ArmCreek, or overflow from Rocky Mouth Creek);• Dissolved oxygen (DO) levels throughout the estuary were generally adequate with a fewinstances when median levels dropped below 80% saturation in the upper estuary (i.e. Site 2),presumably related to rainfall events and associated discharges from tributaries and maybeRocky Mouth Creek. There was one instance when levels throughout the estuary dropped below6 mg/L (~60% oxygen saturation) and this was associated with an event which occurred in April2007. The nature and specific details of the event are unclear;• Conductivity through the estuary during dry periods was observed to reach a maximum of 45mS/cm (median ~ 29 mS/cm) at the upstream end of the estuary with the downstream end ataround 53 mS/cm (reflecting ocean conductivity). During periods of rainfall and catchmentinflows conductivities can fall to 0 mS/cm (i.e. entirely fresh) for large flood events orconductivities may decrease in the upper reaches for a period of time with lower reaches stillrecording near oceanic conductivities;G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-27• Total Nitrogen (TN) concentrations within the estuary increased in a roughly linear fashionbetween sites from the downstream end to the upstream end. Median TN concentrations at theupstream end (i.e. Sites 1 and 2) were found to be above the ANZECC trigger values, theconcentrations at the downstream end were below the trigger values. During periods of lowcatchment inputs, TN concentrations at the upper end of the catchment may decrease below thetrigger value, but tend to spike during periods of rainfall when catchment inflows enter theestuary. A large spike in TN occurred throughout most of the estuary associated with the flood inearly 2008. This is likely to be a result of Richmond River flooding through the Tuckombil Canal;• Results and trends for Total Phosphorus (TP) were found to be very similar to that for TN, i.e.lowest concentrations at the downstream end increasing with distance upstream. Median TPvalues throughout the estuary exceeded ANZECC trigger values at Sites 1, 2 and 3 andcomplied at sites 4 and 5. Concentrations of TP tended to spike with catchment runoff eventsand the event of early 2008 caused significant spikes in TP concentrations throughout the upperand mid reaches of the estuary;• Turbidity concentrations exhibit a trend from low levels in the lower estuary to higher levels at theupstream end. Median levels at the upstream end (sites 1 and 2) were above both the ANZECCtrigger value of 10 NTU and DECCW interim trigger value of 5 mg/L. Downstream sites 3, 4 and5 were below both trigger values, except in periods of significant catchment inflows and thenturbidity levels were observed to increase through the estuary, with highest levels observed atthe upper extents of the estuary. Interestingly, turbidity and total suspended solids (TSS) are notentirely reflective of each other; this indicates that other substances such as tannins maycontribute to turbidity, particularly in the upper reaches;• Metal concentrations are observed to increase in a roughly linear fashion between sites from thedownstream end to the upstream end, with concentrations near Site 1 being quite significantlyhigher than in other areas of the estuary. The reasons for this are unclear at this stage but maybe related to groundwater or other inflows potentially from nearby acid sulphate soil areas; and• Median faecal coliform counts indicate that both primary and secondary contact recreationstandards would be achieved throughout the estuary during dry weather periods. High faecalcoliform counts may be observed in the estuary after rainfall events. This is typical of manyestuaries in the North Coast region. See also section 2.6.1, which discusses Beachwatch data.This program did identify that one site in the Evans River did on occasion fail to meet the passcriteria.DECCW DataIn addition to the comprehensive water quality datasets compiled by Council, DECCW have collectedsome additional water quality datasets including:• Chlorophyll-a;• Ammonia;• Phosphate;• Nitrogen Oxides;• Silica;• Total Dissolved Phosphorus;G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-28• Total Dissolved Nitrogen;• Total Phosphorus (this was also collected by Council); and• Total Nitrogen (this was also collected by Council).From these results, the following additional values were derived:• Dissolved Inorganic Nitrogen (Ammonia + Nitrogen Oxides);• Dissolved Organic Nitrogen (Total Dissolved – Dissolved Inorganic N); and• Dissolved Organic Phosphorus (Total Dissolved Phosphorus – Phosphate).Furthermore, the following datasets were collected by DECCW:• Colour; and• Physico-chemical (including secchi disk depth, temperature, pH, electrical conductivity, dissolvedoxygen, salinity, turbidity, etc). Profiling (i.e. sampling at different depths) has been conductedusing a water quality sonde to collect these data.Box and whisker plots of nutrient and chlorophyll-a data collected by DECCW is presented in Figure2-21, Figure 2-22 and Figure 2-23. ANZECC (2000) WQO have been included in Figure 2-21 andFigure 2-22, while the DECCW WQO is included in Figure 2-23. It should be noted that DECCW hasnot extensively quality assured all data provided at this stage.DECCW data has been collected on 13 separate sampling trips in 2007, 2008 and 2009, althoughdata for nutrients has been extracted from six sampling events undertaken on 12/09/2007, 9/10/2007,27/11/2007, 13/02/2008, 12/03/2008 and 22/04/2008. Of these data samples, the samples collectedin 2008 are likely to have been affected by the large flood event which occurred in January 2008.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-291400Total Nitrogen1000Total Dissolved Nitrogen900Dissolved Organic Nitrogen12001000TN (µg/L)800600400200TDN (µg/L)900800700600500400300200100DON (µg/L)8007006005004003002001000ENV1EVN20ENV1EVN20ENV1EVN2Min OutlierMax OutlierMin OutlierMax OutlierMin OutlierMax Outlier140Dissolved Inorganic Nitrogen60Ammonia60NOx1205050DIN (µg/L)100806040Ammonia (µg/L)403020NOx (µg/L)4030202010100ENV1EVN20ENV1EVN20ENV1EVN2Min OutlierMax OutlierMin OutlierMax OutlierMin OutlierMax OutlierFigure 2-21 DECCW Nitrogen Water Quality Data (6 samples per site)250Total Phosphorus80Total Dissolved Phosphorus60Phosphate200706050TP (µg/L)150100TDP (µg/L)504030Phosphate (µg/L)403020502010100ENV1EVN20ENV1EVN20ENV1EVN2Min OutlierMax OutlierMin OutlierMax OutlierMin OutlierMax OutlierFigure 2-22 DECCW Phosphorus Water Quality Data (6 samples per site)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-3060Electrical Conductivity60Chlorophyll-a5050EC (mS/cm)403020Chlorophyll-a (µg/L)40302010100ENV1EVN20ENV1EVN2Min OutlierMax OutlierMin OutlierMax OutlierFigure 2-23 DECCW Electrical Conductivity and Chlorophyll-a Water Quality Data (13samples per site)The DECCW data indicates that dissolved nitrogen species accounts for around two-thirds of the totalnitrogen concentration. Dissolved organic nitrogen species accounted for nearly all of the totaldissolved nitrogen, with concentrations of inorganic species such as NOx and ammonia being wellbelow guideline levels.Similarly, filterable reactive phosphorus (the fraction that is available for biological uptake) is seen tomake up a small proportion of the total phosphorus recorded (below guideline values), while the totalphosphorus levels were above guideline values.Overall, the results are indicative of a waterway influenced by organic nutrients which are likely to bederived from catchment runoff.The median chlorophyll-a data indicates that concentrations were in the range of 0.5 to 10 µg/Lrecommended by ANZECC (2000), but in exceedence of the 2.3 µg/L trigger value recommended byDECCW for waters with an electrical conductivity greater than 25 mS/cm.2.6.2.3 Key PointsA substantial amount of useful water quality information has been compiled for the Evans River since2006. The information compiled will provide improved understanding of water quality processeswithin the Evans River and will be utilised in establishing the advection-dispersion (AD) model as partof this study (see Section 6).The data compiled by Council and DECCW reinforces similar findings from earlier studies, such asthe Evans River Estuary Processes Study (PBP, 1999a) that identified the presence of water qualityissues at the upper end of the Evans River (i.e. from Doonbah locality up to the weir) as a result ofdischarges from Brandy Arm Creek and overflows from Rocky Mouth Creek. The Council andDECCW identifies that chlorophyll-a, turbidity, TN and TP concentrations during dry weather exceedthe ANZECC guideline trigger values as well as the DECCW interim trigger values.Councils monitoring Sites 3, 4 and 5 were observed to provide water quality results generally withinthe acceptable ranges of the ANZECC and DECCW interim trigger values.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-312.7 Sewage Treatment Plant Flow and QualityCurrent Operating DataParameter/StatisticInformation on the Evans Head Sewage Treatment Plant flow and quality has been provided byCouncil for use in the study. Basic statistical data for selected key pollutants has been included inTable 2-5 to allow for an appreciation of the quality and quantity of flow being discharged from theupgraded plant. Iron, aluminium and oil and grease were not considered to be key potentialpollutants and were not considered.Table 2-5 Evans Head STP Treated Effluent Flow and Quality Data (June 2008 to Sept 2009)TotalNitrogenAmmonia Nitrate NitriteTotalPhosphorusTotalSuspendedSolidsBiologicalOxygenDemandFaecalColiformsUnits mg/L mg/L mg/L mg/L mg/L mg/L mg/L Cfu/100mL pH units ML/dayMedian 5.10 0.31 3.40 0.14 0.205 8.0 1.0 2.0 7.0 1.37Average 5.55 0.58 3.64 0.32 0.238 8.6 1.2 4.7 6.9 1.5510th perc. 3.70 0.15 2.00 0.04 0.110 4.0 0.0 0.0 6.7 1.0490th perc. 7.37 1.27 4.66 0.25 0.347 15.6 3.0 8.8 7.2 2.22Maximum 21.00 4.00 20.40 4.81 0.820 25.0 5.0 50.0 7.3 5.03Count 64 64 63 64 64 63 64 63 63 473pHFlowThese current operational data for the Evans Head STP will conservatively be assumed to bedischarge quality for the future or ultimate (2050) discharges. It is possible that the plant will bemodified in some respect prior to 2050, however, it is expected that concentrations of pollutants withinthe discharge would decrease and not increase as a result of any modification.When these data are considered in the context of water quality conditions within the Evans Riverestuary (see Section 2.6.2 and Figure 2-20 and Figure 2-21), the following key observations aremade:• Median concentrations of Total Nitrogen, Ammonia, Nitrate, Nitrite and Total Phosphorus in STPeffluent are in excess of median water quality conditions within the Evans River and may presenta risk to estuarine water quality;• Median concentrations of Total Suspended Solids (TSS) in STP effluent are at levels equal to orlower than median water quality conditions within the Evans River estuary and are notconsidered to pose a risk to estuarine water quality. There are no guideline trigger valuesavailable for TSS; and• Median concentrations of Faecal Coliforms in STP effluent are at levels equal to or lower thanmedian water quality conditions within the Evans River estuary, which in turn are lower than thecurrent ANZECC guideline trigger values for primary and secondary contact recreation. Hencedischarges of Faecal Coliforms are not considered to pose a risk to estuarine water quality;• Median Biological Oxygen Demand (BOD) concentrations are low at 1 mg/L and are at levelsequal to or lower than median water quality conditions within the Evans River estuary and are notconsidered to pose a risk to estuarine water quality. There are no guideline trigger valuesavailable for BOD; and• Median pH levels in the STP effluent are similar to levels in the upper estuary, although they areslightly more acidic than conditions in the lower estuary. The STP effluent is within ANZECCG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-32guideline trigger values. The pH of discharges is not considered to pose any risk to estuarinewater quality, particularly due to the very large dilution that would be achieved for the more acidicdischarges to the lower estuary.Median discharges of STP effluent to the estuary are currently 1.37 ML/d and are forecast to increaseto around 1.9 ML/d in 2050 (Hydrosphere, 2010). These quantities of flow remain insignificant inrelation to typical tidal exchange volumes within the estuary. ADCP measurements undertaken byBMT WBM as part of the study have been used to estimate tidal exchange volumes (see Section 2-1). On a small neap tide cycle at the entrance, the daily STP discharge would constitute less than0.1% of the daily tidal exchange volume. As such, significant dilution of the freshwater STPdischarge within the saline receiving waters of the lower estuary would occur. Based on theestimated levels of dilution, discharge of low saline STP effluent is not considered to pose a risk toestuarine water quality in these locations.Future Operating DataAssessments to be performed as part of this study are intended to focus on future or “ultimate”conditions in 2050. Flow estimate at this time take into account future population growth in thesewage catchment of Evans Head STP and for other factors which may reduce long term inputs tothe treatment plant, such as infiltration reduction.Information for use in the study has been documented in the report ‘Analysis of Evans Head STPFlows, Interim Report’ (Hydrosphere, 2010) (included in Appendix B) which was completed to providea time-series of outflows from the STP to be considered as inputs to the estuary.The assessments performed in Hydrosphere (2010) have included an analysis of STP inflow data. Inparticular the study has investigated the impacts of:• Groundwater levels and inflows to the STP;• Higher loadings that may be experienced during holiday periods;• Influence of dry weather on STP inflows; and• Influence of tidal cycles of STP inflows.The key findings of this phase of the study were as follows:• “Maximum instantaneous STP inflow is affected by surging past the step screen and shows nosignificant relationship to the daily STP inflow;• Rainfall events have a significant impact on groundwater levels. The duration and magnitude ofthis effect depends on the magnitude, duration and frequency of rain days;• Periods of high STP inflow correspond with periods of high groundwater table and wet weather;• During dry weather, the STP inflow remains relatively constant with non-holiday loading atapproximately 1.063 ML/d;• The effect of holiday loads on STP inflows is not as significant as the effect of wet weather; and• Tides do not have a significant impact on groundwater level or STP inflows.”G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DATA COLLECTION AND REVIEW 2-33To generate the ultimate (2050) time series of flows for use in this study, Hydrosphere (2010)generated a synthetic series of data using the historical climatic conditions represented by the STPflows between October 2007 and February 2010 and taking account of:• Increases in population being serviced by the STP;• Reductions in dry weather ground infiltration as a result of ongoing schemes to limit infiltrationrates; and• Reductions in wet weather flows as a result of ongoing schemes to limit infiltration rates.Furthermore to allow for time series to be generated for ebb-tide release scenarios (as well ascontinuous release scenarios), Hydrosphere (2010) have developed conceptual schemearrangements which allow for the storage and transfer of effluent. The effect of the schemearrangements has been reflected in the time-series of flows (for continuous and ebb-tide release)utilised in this study. Refer to Appendix B for further information.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-13 REVIEW OF ESTUARY PROCESSESThe physical, chemical and biological processes of estuarine environments, such as the Evans Riverestuary are highly inter-related. The process interactions for the estuary are shown schematically inFigure 3-1.In simple terms, external processes (such as those which govern entrance condition and catchmentinputs) influence the internal physical hydraulic processes, which in turn influence the sedimentaryand water quality responses, which in turn, define the ecological structure of the estuary.Figure 3-1Schematic of Estuarine Process InteractionsThis section provides a review of these key estuarine processes and associated responses usingavailable information. The review has been tailored towards developing an understanding of theflushing and assimilative capacity of the Evans River to accept treated sewage effluent. As outlinedin the study brief the following were identified as key points to address:• Flow characteristics;• Response to rainfall and flood events;• Response to tides;• Ecosystem characteristics;• Water quality characteristics (spatial and temporal variability, tidal variability); and• Comparison of modelled conditions with identified social and environmental values.These aspects and more are addressed in the following sections.3.1 Entrance ConditionsThe entrance of the Evans River is trained by twin breakwaters which were constructed in the early1960’s to improve boating navigation through the entrance. Estuarine conditions would haveG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-2changed at that time in response to the construction of the walls. However, it is expected that thecondition of the entrance has now stabilised, and conditions in the lower estuary are now in a form ofdynamic equilibrium between the controlling forces of the tide and fluvial activity of the river and thelittoral processes of the adjacent beaches.As such, the configuration of the river and entrance channels as well as the adjacent coastline islikely to be continually changing under the natural variability of the prevailing conditions. Thefollowing general observations are made for entrance conditions in the Evans River:• During normal day-to-day tide and wave conditions, there is a general tendency for gradualsediment infeed from the beach system. The rate is typically increased following scour from aflood event and decreased at times when the entrance is shoaled. As shoaling of the entranceregion continues, this has the effect of constricting the channel and reducing the tidal range withlower high tides and higher low tides; and• Fluvial or flooding activity can have dramatic short-term effects with high flows and velocitiestransporting large quantities of sediment downstream and into the littoral drift beach system.These events have the ability to alter the bed characteristics of localised areas of the river andentrance due to the amounts of sediment that may be transported and redeposited overrelatively short periods. Scour of river entrances is a typical characteristic of flood events. Thisresults in a more hydraulically efficient entrance with a subsequent increase in tidal range andflow within the estuary.The Estuary Processes Study (PBP, 1999a) reviewed entrance conditions of the Evans River byestimating sand fluxes between the estuary and ocean. This sediment budget approach led into areview of shoaling patterns and the likely penetration of ocean sands into the estuary and theircirculation in the entrance zone.The EPS determined that there was a net ocean infeed of sand to the Evans River (not during floodyears), although the exact rate was not quantified, and was recommended for further investigation.The extent of the penetration of these materials was identified to be at the approximate limit of oceanswells into the estuary, as these facilitate sand ingress on flooding tides. It was identified that thelikely limit of swell penetration was to where Woodburn Street meets the estuary (i.e. a few hundredmetres downstream of the Elm Street Bridge).The EPS suggests that while floods scour the entrance shoals, the entrance is dynamically stableand that flood scour and net tidal influx of sand are approximately balanced. Figure 3-2 shows aerialimagery of the lower estuary at different times.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-3Figure 3-2Aerial Photographs of Lower EstuaryThe first image (on the left) was included in GHD (2006a). The date of the aerial image used in thisreport is unknown. The image on the right uses aerial photography data provided by Council(captured January 2009). It is likely that the two images have been captured within several years ofeach other as there are limited observed changes in the buildings within Evans Head (i.e. newbuildings). The two images appear to have been captured on different tides but demonstrate similarshoaling patterns and characteristics in the entrance zone up to the location of the bridge andbeyond. Further interrogation of historical photography would provide further evidence of changes inshoaling patterns (the focus would necessary be post-breakwater construction, i.e. 1960s onwards).Given the likely permanency of the breakwaters and associated stability of the entrance shoals,noting that they oscillate through flood (scour) and dry (accretion) periods, it is unlikely that entranceconditions are relatively stable.The hydrosurvey information which has been used in this study (see Section 2.5) used data from twoperiods, i.e. 2006 for within the estuary and 1997 for areas outside of the estuary. Exact conditions atthe time of the hydrosurvey are unknown, although conditions could be inferred from antecedentrainfall records which would indicate if there had been any major flood events within the estuary priorto the surveys (see Section 3.2 which discusses internal and external catchment inputs).3.2 Catchment Inputs3.2.1 Internal Inputs‘Catchment inputs’ refers to the sediment, nutrient and other inputs contributed to the Evans Riverfrom its catchment. Catchment inputs are primarily defined by the aspects of catchment size andhydrology, landuses and local climate factors such as rainfall and evaporation. Major namedcatchment inputs include the Woodburn Drain which drains agricultural areas in the upper catchmentnear Woodburn. Additionally, there are catchment inputs from Brandy Arm Creek, a tributary whichdrains mainly forested areas also in the upper catchment. Other catchment inputs enter the river viaunnamed creeks typically draining through low-lying wetland areas.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-4In the case of the Evans River, there are external inputs which can periodically enter the catchment,typically during flood events via the Tuckombil Canal. These external inputs are derived from theRichmond River catchment and are described separately.LanduseThe Estuary Processes Study (PBP, 1999a) described the Evans River as, “one of the least disturbedon the North Coast of NSW”, with approximately 84% of the catchment (at that time) in a naturalstate.As part of this current study, BMT WBM has developed a catchment model of the Evans River (seeSection 4). As part of the model development, current land statistics have been recalculated usingup-to-date land use classification data, as presented in Table 4-2. The key findings of this include:• Forested lands occupy 75.1% of the catchment;• Grazing occupies 11.4%;• Intensive uses (i.e. industry, special purpose) occupy 3.1%;• Rural residential lands occupy 4.1%;• Urban residential lands occupy 1.8%; and• Sugar cane and horticulture occupy 1.5%.Although it is difficult to directly compare current results to results presented in the EPS due to theuse of different land use designations, it is suggested that there has been little change in land-useover the previous decade.Catchment FlowsThe WaterCAST catchment model prepared by BMT WBM for this study takes into accountcatchment size and hydrology, landuses and local climate factors such as rainfall and evaporation inpredicting catchment inputs. The model results are presented in Section 4.3 and specifically Table4-3. Over the 10 year period assessed, it was found that catchment inflows accounted forapproximately 51% of the total inflows to the Evans River.This is consistent with the findings of the Estuary Processes Study (PBP, 1999a) which indicates thatthe catchment contributed around 56% of the total inflows to the Evans River. It should be noted thatthese calculations were performed during the period when the Tuckombil Canal fabridam (referSection 3.2.2) was still operational.Catchment LoadsCatchment pollutant loads were not included as inputs to the advection-dispersion (AD) model, thereasons for which are discussed in Section 4. A more detailed water quality model could includecatchment loads and should be considered for additional studies.Driven by catchment hydrology and landuse, the WaterCAST model provides estimates of pollutantloads from the catchment to the Evans River. External inputs determined from overflows via theTuckombil canal were incorporated into the model. The model results are presented in Appendix D.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-5WaterCAST model results were consistent with findings in the Estuary Processes Study (PBP,1999a) and indicate that the external catchment loads of suspended solids and nutrients can besignificant in relation to the typical internal catchment loads, with the magnitude of the external inputsbeing related to the size of the overtopping event which introduces external floodwaters to the EvansRiver estuary.3.2.2 External InputsIn addition to catchment inputs, flood flows from the Richmond River / Rocky Mouth Creek, enteringvia the Tuckombil Canal, have the potential to input large quantities of sediments and nutrients to theEvans River. The Estuary Processes Study predicted these inputs to be approximately the samemagnitude, on an annual load basis, as those pollutants derived solely from the Evans Rivercatchment.The Tuckombil Canal is a manmade waterway connecting the Evans River to Rocky Mouth Creek,which itself is part of the Richmond River system. The canal functions as a flood relief for theRichmond River, alleviating flood levels and reducing inundation times across the floodplain to thewest of Woodburn. The canal was excavated to its current form in 1965. Originally a fabridam wasused to control flooding and tides. Due to numerous failures, the fabridam was replaced in 2001 witha ‘temporary’ fixed concrete weir at 0.94m AHD. The current weir structure located immediatelybelow the Pacific Highway just to the south of Woodburn is shown in Figure 3-3. The weir representsthe upstream tidal limit of the estuary and is also on the catchment boundary of the Evans River.Figure 3-3Tuckombil WeirThe flood relief function of the Tuckombil Canal (and weir) is likely to have influenced thehydrodynamics of both the Richmond and Evans Rivers systems as detailed in the Geolink et al(2008):• “operation of the canal is likely to have approximately doubled the total volume of freshwaterbeing discharged by the Evans River each year (PBP, 1999a);• peak flood discharges into the Evans River from the Richmond are likely to have increased; andG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-6• flows from the canal are likely to have changed the fluvial regime and the geomorphology of theEvans River, which had previously evolved in response to more local catchment flows.”Further consideration of the type of weir, its height and operation has been recently reviewed as partof the ‘Tuckombil Canal - A report regarding a replacement structure for the Canal’ (Geolink et al,2008) and other flood related studies completed by BMT WBM for the Richmond River CountyCouncil. Any future changes to the weir height and operating status of the canal or weir may requirea reassessment of the flood (and or tide) related inflows to the upper Evans River and associatedinfluences on hydrodynamics (i.e. tidal flushing, recovery after floods, etc) of the Evans River.Richmond River County Council will be able to advise Council on the future of the Tuckombil Weirand any potential changes which may occur in respect of its height and function.For the purposes of hydrodynamic and advection-dispersion modelling (see Section 4) estimates offlows and pollutant loads entering the Evans River from the Richmond River / Rocky Mouth Creek viathe Tuckombil Canal were required to be developed. This information was used as ‘boundarycondition’ data within these models. With the information built into the models, they are forced tosimulate the effects of external flows and loads entering the system. Consequently, the modelsprovide a more accurate representation of the effects of flooding events on estuary salinity andassociated recovery after flood events.To determine the external flow and loads entering the estuary, BMT WBM developed a method toconvert water levels in Rocky Mouth Creek to weir overflows into the Evans River. Essentially, theprocess used recorded (MHL) water level data in Rocky Mouth Creek at the location of the PacificHighway bridge (which is immediately adjacent to the Tuckombil Canal) to determine when waterlevels exceed the weir height. A simple weir calculation, based on the specific cross section of theTuckombil weir and adjoining channel was then used to convert the water heights into inflow. Figure3-4 shows the tide recorder with the Tuckombil weir located immediately behind it.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-7Figure 3-4Rocky Mouth Creek Pacific Highway Bridge Tide RecorderIt should be noted that these calculations assume that there are no tailwater effects within theTuckombil Canal affecting weir overflows, calculations also assume no blockages with debris. It isacknowledged that these are significant assumptions, however, a more sophisticated hydraulic modelof Rocky Mouth Creek, Tuckombil Weir and Tuckombil Canal would be required to more accuratelypredict weir inflows. This level of assessment is beyond the scope of the current study.An example of a flooding event which occurred in June 2005 is shown in Figure 3-5. The figureshows a rapid increase in water levels across a one day period at the tide recorder on the PacificHighway Bridge over 29 th and 30 th June. These water levels are maintained for the next three daysuntil the flood resides and the tidal signal is once again evident about one week after thecommencement of the flood. In this flood, flood heights peaked at around 2.0 m AHD and the tidegauge provided peak discharges of up to 10,000 ML per day. It should be noted that in these figures,the weir discharge is shown to start to occur prior to the flood height reaching 0.94 m AHD. This issimply a function of the way the data has been graphed and does not represent actual conditions.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-8June 2005 Flood Event ‐ Rainfall at Evans Head and Calculated Tuckombil Weir Discharge30012,000250rainfallweir discharge10,000Rainfall (mm)2001501008,0006,0004,000Discharge (ML/d)502,0000022 Jun 05 23 Jun 05 24 Jun 05 25 Jun 05 26 Jun 05 27 Jun 05 28 Jun 05 29 Jun 05 30 Jun 05 01 Jul 05 02 Jul 05 03 Jul 05 04 Jul 05 05 Jul 05 06 Jul 05 07 Jul 05DateJune 2005 Flood Event ‐ Pacific Highway Bridge Tide Levels and Calculated Tuckombil Weir Discharge2.512,0002Water Levelweir discharge10,000Tide Level (m AHD)1.510.58,0006,0004,000Weir Discharge (ML/d)02,000‐0.5022 Jun 05 23 Jun 05 24 Jun 05 25 Jun 05 26 Jun 05 27 Jun 05 28 Jun 05 29 Jun 05 30 Jun 05 01 Jul 05 02 Jul 05 03 Jul 05 04 Jul 05 05 Jul 05 06 Jul 05 07 Jul 05DateFigure 3-5June 2005 Flooding EventCurrent available water level information (post weir construction to February 2010) provides for thefollowing periods of weir overtopping and associated total discharge volumes:• 25 February 2004 to 27 February 2004 – 1,500 ML;• 6 March 2004 to 9 March 2004 – 8,200 ML;• 30 June 2005 to 5 July 2005 – 29,300 ML;• 19 January 2006 to 23 January 2006 – 10,000 ML;• 4 March 2006 to 8 March 2006 – 13,500 ML;• 5 January 2008 to 12 January 2008 – 42,100 ML;• 30 March 2009 to 11 April 2009 – 16,500 ML;• 20 May 2009 to 2 June 2009 – 183,300 ML; and• 21 June 2009 to 28 June 2009 – 3,200 ML.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-9The earlier stated limitations of the approach used to calculate weir flows should be considered ininterpreting these results. Also, MHL input data for the tide recorded on the Pacific Highway Bridgewas not operating during the period 20 December 2007 through to 20 June 2008. For this period,tidal records for Rocky Mouth Creek were used as a surrogate measure of tidal height for thepurposes of calculating weir overtopping. Figure 3-6 provides a comparison of tidal records at bothrecorders over the period of interest. While there are likely to be minor differences in the tidalrecords, the use of Rocky Mouth Creek data was used for the purposes of estimating flood flows tothe Evans River.Figure 3-6 Comparison of tide heights over December 2007 to June 2008The WaterCAST catchment model prepared by BMT WBM for this study (see Section 4.3 andspecifically Table 4-3) identifies that over the 10 year period assessed, Tuckombil Canal inflowsaccounted for approximately 49% of the total inflows to the Evans River.In terms of water quality data for external inputs to the Evans River, the tide recorder at Rocky MouthCreek records some basic physical water quality parameters in addition to recording tide levels.These datasets include temperature, pH, salinity and dissolved oxygen. Raw data from this site wasobtained from Dec 2005 to April 2010 (data provided by Richmond River County Council). Thesalinity levels were determined at times of overflow into the Evans River and the inputs of salinitywere included in the boundary condition files of the advection-dispersion model.Also, there are likely to be significant concentrations of other pollutants entering the Evans River attimes of weir overflow. For the purposes of catchment modelling, previously establishedconcentrations of key pollutants including Total Nitrogen, Total Phosphorus and Total SuspendedSolids were adopted from the Estuary Processes Study (PBP, 1999a) as detailed in Appendix D.The WaterCAST catchment model prepared by BMT WBM for this study (see Section 4.3 andspecifically Table 4-3) identifies that over the 10 year period assessed, Tuckombil Canal inflowsaccounted for approximately 85% of Total Suspended Solids, 32% of Total Nitrogen and 56% of TotalPhosphorus (TP) loadings to the Evans River.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-103.3 SedimentsIn respect of fluvial sedimentary processes, the Estuary Processes Study (PBP, 1999a) developed aconceptual understanding of sedimentary processes which drew on all information available at thattime. The model identified:• Different sedimentary patterns existed upstream and downstream of Brandy Arm Creek, with theupstream section containing muddy sediments with actively accreting river banks and thedownstream section containing sandy sediments with banks actively eroding and the bedscouring;• Additional flows and sediment loads enter the Evans River through the Tuckombil Canal. Theseadditional flows and loads will affect the natural hydrodynamics of the river and the associatedsedimentary processes. It is likely that the inflows are forcing the Evans River to adjust to thenew hydraulic conditions;• Active accretion is likely to be occurring between Iron Gates and the Elm Street Bridge. Thissediment is likely to be being sourced from the erosion of riverbanks and bed between BrandyArm Creek and Iron Gates; and• The majority of the catchment or Richmond River derived fine sediments are transported throughthe system and discharged to the ocean during high flow events (e.g. floods).These findings are relevant to this study in that the sedimentary patterns and hence tidalhydrodynamics will continue to alter upstream of Iron Gates until a stable river form is achieved. Thelower estuarine hydrodynamics will be dominantly influenced by entrance conditions such as theentrance shoal and bar. As discussed in Section 3.1, these systems were reported in the EstuaryProcesses Study to be dynamically stable with balanced rates of flood scour and tidal influx.The Evans River upstream of the location of Brandy Arm Creek would appear to provide relativelyquiescent conditions suitable for settling of finer materials and hence it is anticipated that tidalexchange rates in this vicinity would be low.Material types and dispersion rates within the upper section of estuary, to represent the variation insediments (i.e. friction) and mixing (i.e. dispersion) were adjusted in the hydrodynamic and advectiondispersionmodels to allow them to best represent these identified conditions (see Section 6).3.4 Estuarine HydrodynamicsTides constitute one of the key driving processes of the Evans estuary. Tidal action pushes oceanwaters into the estuary thereby forcing tidal mixing and exchange. The efficiency of these processesvaries through the estuary in line with the degree to which the tides can propagate through theestuary. Tidal energy is dissipated with travel along estuaries from the mouth as a result of friction(mainly with the estuary bed) and other hydraulic losses (constrictions in the channel, bridges, etc).The tides and associated tidal processes of the Evans River have been reviewed in a number ofstudies. The Estuary Processes Study (PBP, 1999a) provides a relatively recent account of keyprocesses. This study reviewed a number of earlier studies and datasets.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-11Also, MHL has undertaken an extensive data collection exercise on the Evans River on behalf of thethen Department of Natural Resources, over a six month period from 2005 to 2006. The aim of theexercise was to facilitate a better understanding of hydraulic flushing and mixing processes of theEvans River. As part of the data collection exercise, tide recorders were deployed at eight sitesalong the length of the estuary, and additional tidal velocity and volumetric discharge assessments(i.e. ADCP transects) were undertaken across a flood-ebb diurnal tidal cycle, during a spring tide (i.e.a period characterised by higher high tides, lower low tides and increased tidal velocities andvolumetric exchange across the tidal cycle).Key findings and conclusions from the Estuary Processes Study and MHL study are outlined in thefollowing sections.3.4.1 Tidal PlanesTidal planes represent water levels within the estuary at various states of the tide. Comparison oftidal planes at various locations within the estuary can provide an understanding of tidal propagationthrough the estuary and likely tidal exchange.The most recent study providing detailed information on tidal planes within the estuary is contained inthe MHL (2006) investigation as detailed in Table 3-1 and Figure 3-8. Details of the sites used forrecording tide levels are shown in Figure 3-7. Please note that Site 0 is not shown on the figuresbelow, as it represents tide data collected at Coffs Harbour.Figure 3-7 Locations of Tide Recording (MHL, 2006)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-12Tidal Planes Site 0(m AHD)Table 3-1 Comparison of Tidal Planes (MHL, 2006)Ocean Evans River Tuckombil CanalSite 2(m AHD)Site 4(m AHD)Site 5(m AHD)Site 6(m AHD)Site 7(m AHD)Site 9(m AHD)Site 10(m AHD)Site 11(m AHD)HHW(SS) 1.133 1.100 - 1.056 1.008 - 0.875 0.882 0.869MHWS 0.738 0.701 - 0.660 0.620 - 0.530 0.537 0.522MHW 0.589 0.554 - 0.549 0.525 - 0.463 0.466 0.452MHWN 0.439 0.406 - 0.437 0.429 - 0.396 0.395 0.382MTL 0.056 0.045 - 0.104 0.117 - 0.145 0.146 0.129MLWN -0.326 -0.317 - -0.229 -0.195 - -0.105 -0.102 -0.124MLW -0.476 -0.465 - -0.341 -0.291 - -0.172 -0.173 -0.194MLWS -0.626 -0.612 - -0.453 -0.387 - -0.240 -0.245 -0.264ISLW -0.907 -0.897 - -0.735 -0.663 - -0.486 -0.491 -0.512HHW(SS) – Higher High Water (Spring Solstices); MHWS – Mean High Water Spring; MHW – Mean High Water; MHWN –Mean High Water Neap; MTL – Mean Tide Level; MLWN – Mean Low Water Neaps; MLW – Mean Low Water; MLWS – MeanLow Water Springs and ISLW – Indian Spring Low waterFigure 3-8 Tidal Planes for Data Collected 7/12/05 to 19/01/06 (MHL, 2006)The tidal plane information identified in Table 3-1 and Figure 3-8 show expected reductions in tidalplanes as a result of significant hydraulic structures and as a result of bed friction with increasingtravel along the estuary. Tidal planes reduce initially across the entrance (i.e. between Site 0 andSite 2) and then remain relatively constant up to Site 5 at the downstream end of Iron Gates.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-13Tidal planes contract significantly across Iron Gates (i.e. between Site 5 and 6) and then continue tocontract up to around Site 9 which is as the end of Brandy Arm Creek, approximately 11km from theestuary entrance. Between Site 9 and Site 11, the estuary straightens and widens (particularly in thelocation of the Tuckombil Canal) and as a result the tidal planes tend to remain constant.The tidal plane information will also be indicative of relative degree of tidal flushing, with the largestdifferences in tidal planes at a site representing the highest levels of tidal exchange and henceflushing. The MHL data indicates that tidal flushing rates would increase downstream of Site 9 andreach a maximum value near the entrance.Tidal planes can change as a result of changes in shoaling patterns as a result of floods andaccretion or erosion of sediments within the estuary. The Estuary Processes Study identified thatshoaling may have been occurring in the upper estuarine areas with little shoaling occurring in thelower section (i.e. downstream from Iron Gates to the Elm Street Bridge). A thorough review ofshoaling within the estuary is outside the scope of this study, although it remains an importantconsideration for any upper estuarine discharge scenarios that may be considered, as shoaling willaffect tidal levels and associated exchange.Tidal level information collected as part of this study (see Section 2.1.1) was collected for thepurposes of model calibration and validation and does not necessitate specific mention in thissection.3.4.2 Tidal LagsTidal lags are defined as the time delay for a specific tide (e.g. mean high water springs) between anytwo locations within an estuary. MHL (2006) includes specific details of calculated tidal phasedifferences for all tidal planes from the entrance (i.e. ocean levels recorded at Coffs Harbour) to theTuckombil weir. The MHL report identified that the following tidal lags for all tidal planes (i.e. all tidalplanes have been averaged to provide a single result):• Site 2 – 6 minutes (standard deviation 5 minutes);• Site 5 – 37 minutes (standard deviation 14 minutes);• Site 6 – 60 minutes (standard deviation 19 minutes);• Site 9 – 141 minutes (standard deviation 35 minutes);• Site 10 – 149 minutes (standard deviation 38 minutes); and• Site 11 – 146 minutes (standard deviation 38 minutes).It is noted that tidal lags are relatively short up to around site 5 (downstream of Iron Gates) and in therelatively short travel distance through Iron Gates (~500m), tidal lag times nearly double. Tide lagsincrease dramatically from Site 6 to Site 9. Upstream of site 9, tidal lags remain relatively constant.The timing of tidal lags will be an important future design consideration for any discharge optionswhich rely on currents to remove effluent from the estuary during a tidal cycle.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-143.4.3 Tidal PhasingEstimates of tidal phasing (i.e. difference in time between high or low tide slack water and peak ebbor flood discharges) were also discussed in the Estuary Processes Study (PBP, 1999a). Furtheruseful information was also obtained by BMT WBM as part of the recent field work.Work completed as part of the Estuary Processes Study (PBP, 1999a) identified that peak flood tidedischarge at the entrance occurs 1.5 hours before high water, while peak ebb-tide discharge occurssome 4 hours before low water, while at the Elm Street Bridge, the peak flood tide discharge occurs 2hours before high water, while peak ebb-tide discharge again occurs 4 hours before low water.Field data collection conducted by BMT WBM in February 2010 (refer Figure 3-9), identified:• For a spring tide at the entrance (i.e. Site Downstream) it was observed that high tide occurred ataround 10:30am with peak flood tide flows occurring at around 1pm, i.e. 2.5 hrs after the peaktide height and about 4 hours prior to low water. For the ebb-tide, low was observed at around4:30pm with peak ebb-tide flows occurring at around 9:30pm, some 5 hours after the minimumtide height, and about 1.5 hours before the next high at 11pm; and• For the spring tide at the upstream site (i.e. Upstream 1) it was observed that high tide occurredat around 1:00pm with peak flood tide flows occurring at around 4pm (estimate), i.e. 3 hrs afterthe peak tide height. For the ebb-tide, low was observed at around 9:00pm with peak ebb-tideflows occurring at around 12:00am, some 3 hours after the minimum tide height, and about 1.5hours before the next high at 1:30am.It can be seen that very similar findings were observed between the Estuary Processes Study andBMT WBM’s field data collection at the entrance.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-15Comparison of Recorded Tide level and Estuary Discharge - Entrance 20 Feb 201020016012080DischargeTide Height10.80.60.4400-40-80-120-160-2000.20-0.2-0.4-0.6-0.8-110:00:00 AM11:00:00 AM12:00:00 PM1:00:00 PM2:00:00 PM3:00:00 PM4:00:00 PM5:00:00 PM6:00:00 PMFlow (m3/s)7:00:00 PM8:00:00 PM9:00:00 PMTide Level (m)10:00:00 PM11:00:00 PM12:00:00 AM1:00:00 AMComparison of Recorded Tide level and Estuary Discharge - Upstream 1, 3 Feb 2010604530DischargeTide Height0.80.60.4150-15-300.20-0.2-0.4-45-0.6-60-0.812:00:00 PM1:00:00 PM2:00:00 PM3:00:00 PM4:00:00 PM5:00:00 PM6:00:00 PM7:00:00 PM8:00:00 PM9:00:00 PM10:00:00 PM11:00:00 PM12:00:00 AM1:00:00 AM2:00:00 AMFlow (m3/s)Tide Level (m)Figure 3-9Comparison of Recorded Tide Heights and Discharge at Sites ‘Entrance’ and‘Upstream 1’G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-163.4.4 Tidal FlushingThe Estuary Processes Study (PBP, 1999a) provides an estimate of flushing times for the EvansRiver. The flushing times were estimated based on salinity regimes, but did not have the support of ahydrodynamic and advection/dispersion model to accurately calculate flushing times.Irrespective of this, the flushing times identified in the Processes Study were as follows:• Lower reaches of the river, i.e. up to Iron Gates < 3 days;• Between Iron Gates and Doonbah ~ 25 days;• Brandy Arm Creek junction ~40 days; and• Tuckombil Canal > 70 days.Updated estimates of tidal flushing could be calculated using the hydrodynamic and advectiondispersionmodels developed as part of this study.3.4.5 Tidal ExcursionBased on the ACDP recording performed by BMT WBM for the project, tidal excursion distanceswere able to be determined. Tidal excursion relates to the maximum distance travelled that may betravelled by a water particle on a tide, i.e. an incoming tide between slack tides. The estimatesprovided have been calculated by multiplying recorded velocities during the ADCP transects (whichaverage velocities across the channel) by the interval in between recording (2 transects every 15minutes). Details of the sites are provided in Figure 2-1.For the ADCP recording performed at the entrance (i.e. site Downstream) the following tidalexcursions were calculated for a spring tide:• Flooding tide – 10.0 km; and• Ebbing tide – 6.7 km.This site was approximately 300 from the estuary entrance and on a strong neap tide such as the onerecorded (i.e. about 1.7m between high and low tide) tidal excursions were found to be high andwaters would be carried well out into the ocean from this point.For the ADCP recording performed at the upstream site (i.e. site Upstream 1) the following tidalexcursions were calculated for a spring tide:• Flooding tide – 6.1 km; and• Ebbing tide – 4.5 km.This site was approximately 10 km from the estuary entrance and even on a strong neap tide such asthe one recorded (i.e. about 0.8 m between high and low tide), it is expected that waters within theestuary at this point would only reach about half way to the entrance.For the ADCP recording performed at the entrance site (i.e. site Downstream) the following tidalexcursions were calculated for a neap tide:• Flooding tide – 1.9 km; andG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-17• Ebbing tide – 2.2 km.The Estuary Processes Study (PBP, 1999a) indicated tidal excursions of between 1.5 and 2.5 kmthroughout the estuary. It is considered that these reported figures are potentially correct, but relatemore to tidal excursions during neap tides. The neap tide monitored by BMT WBM during the studywas a very minor tide (i.e. about 0.3 m between high and low tide) and the results may beapproaching the lower limits of tidal excursion within the estuary (see Figure 2-9 for recorded tideheights).3.5 Water QualitySection 2.6 provides a review of Environmental Values, Water Quality Objectives and comparisons ofexisting data to these objective values. This section aims to provide more process understandingand in particular what tends to happen to water quality within the estuary during floods and dryperiods in different localities in the estuary.3.5.1 Dry WeatherDuring dry weather, tides are found to be the dominant aspect within the estuary regulating waterquality conditions. Dry conditions are characterised by periods where there are low levels ofcatchment runoff (and inputs from external sources such as the Tuckombil Canal).Conditions that allow for catchment runoff to occur vary and will be a function of a number of factorssuch as the intensity of the rainfall, total volume of rainfall and catchment conditions at the time of therainfall. As such, it is difficult to determine exactly what quantity of rainfall will lead to catchmentrunoff being generated. Above this threshold, low salinity water with higher concentrations ofsediment and nutrients will enter the estuary from the catchment.If the duration of the dry is sufficient, near oceanic conductivity (i.e. salinity) levels can be observedthroughout the estuary and extending up to the tidal extent, i.e. at the Tuckombil weir. As can beseen in Figure 3-10, during the period of January 2007 to May 2007 conductivity levels at Site 1reaches 45,000 µS/cm which is approximately 90% of the level typically observed in sea water. Sitelocations are included in Figure 2-19.During this period, Evans Head received 13 mm in January 2007, 49 mm in February, 95 mm inMarch, 153 mm in April and 55 mm in May. Rainfall levels were below seasonal averages in Januarywhich normally sees around 140mm of rainfall, February 170 mm, March 190 mm and May 105mm.Only April had typical rainfall. Seasonal average rainfall figures are presented in Figure 1-2.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-1860,00050,00040,00030,00020,00010,000001/08/0601/09/0601/10/0601/11/0601/12/0601/01/0701/02/0701/03/0701/04/0701/05/0701/06/0701/07/0701/08/0701/09/0701/10/0701/11/0701/12/0701/01/0801/02/0801/03/0801/04/0801/05/0801/06/0801/07/0801/08/08Conductivity (µS/cm)01/09/0801/10/0801/11/0801/12/0801/01/0901/02/09Site 1 Site 2 Site 3 Site 4 Site 5Figure 3-10 Conductivity Time Series, August 2006 to February 2009 (Source Council)Similarly for other water quality constituents, dry periods allow for the concentrations of theconstituents to reduce towards that which would be observed in the ocean. What is observed in theEvans River estuary for many constituents is that there is regular gradation in concentrations from theentrance, which typically records the lowest concentrations (i.e. best water quality) andconcentrations increase from the entrance to the end of the estuary at Tuckombil Weir.To exemplify this point, TN concentrations at Site 1 during the period of January 2007 to May 2007 (adry period) are observed to gradually decrease until May when the lowest concentrations areobserved. Site 1 is at the tidal limit of the estuary and is the most responsive site to catchmentinputs, i.e. concentrations in TN will rise after catchment runoff events. Hence, it can be deduced thatduring dry periods, tides can dominate and improve water quality up to the tidal limit of the estuaryduring dry periods. Concentrations of TN then increase again in June which was a wetter month (seeFigure 3-11).3.002.50TN (mg/L)2.001.501.000.500.00Aug 06Sep 06Oct 06Nov 06Dec 06Jan 07Feb 07Mar 07Apr 07May 07Jun 07Jul 07Aug 07Sep 07Oct 07Nov 07Dec 07Jan 08Feb 08Mar 08Apr 08May 08Jun 08Jul 08Aug 08Sep 08Oct 08Nov 08Dec 08Jan 09Feb 09Site 1 Site 2 Site 3 Site 4 Site 5Figure 3-11 TN Time Series, August 2006 to February 2009 (Source Council) 11 The zero (0) results are a function of the accuracy of the laboratory testing completed to derive the result. If the samplecontains less TN or TP less than was detectable by the laboratory procedure utilised, then this result has been recorded as0, although this is not strictly correct.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-19During this dry period, the concentrations of TN averaged 0.64 mg/L at Site 1, 0.26 mg/L at Site 2,0.14 mg/L at Site 3, 0.09 mg/L at Site 4 and 0.07 mg/L at Site 5 which closely represent the longerterm medians determined from the Council water quality dataset (see Figure 2-20 for box and whiskerplots of Council TN data).3.5.2 Catchment Rainfall Events (No Overtopping of TuckombilWeir)As mentioned in the previous section, the catchment of the Evans River will generate runoff to theEvans River during some, but not all rainfall events. The occurrence of runoff will be a function of anumber of factors such as the intensity of the rainfall, total volume of rainfall and catchmentconditions at the time of the rainfall. Large regional rain events have the capacity to lead to freshes inRocky Mouth Creek or even flooding of the Richmond River. Both of these events either singularly orin combination can lead to water flooding across the Tuckombil Weir into the Evans River.However, certain localised rain events or even large regional events can occur which do not lead toflooding of the Tuckombil Weir. During these events only catchment runoff enters the estuary. Twosuch events were observed to have occurred in November 2007 and July 2008.In November 2007, 210 mm of rain fell from 7 to 11 November, and in July 2008 120mm of rain fellover 24 to 26 July. No corresponding inflows were observed to enter the estuary via the TuckombilWeir. These two events are discussed in more detail below.November 2007Subsequent to the rainfall event on 7 to 11 November 2007, water quality was collected from theEvans River on 8 th November and 30 th November 2007.The sampling on the 30 th November indicated elevated TN concentrations at Sites 1 and 2 with othersites remaining close to the long term median value.In respect of TP (see Figure 3-12), it is noted that results for 30 th November 2007 show a minor spikewith elevated concentrations at all sites.July 2008Subsequent to the rainfall event on 24 to 26 July 2008, water quality sampling was undertaken on22 nd August (quite some time after the event).This sampling event revealed slightly elevated concentrations for TN at Site 2 and 3 (upper to midestuary), but failed to identify any elevations in TP at any location throughout the estuary. It is notedthat the effects may have been diminished as it was nearly a month between the rainfall event andthe water quality sampling event.Overall, for the parameters of TN and TP, the estuary definitely showed a response for the +200 mmrainfall event in November 2007. However, there was no clear estuary response for the 120 mmevent in July 2008 and this may have been attributable to a lack of suitable data with which to assessthe event.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-200.400.350.300.250.200.150.100.050.00Aug 06Sep 06Oct 06Nov 06Dec 06Jan 07Feb 07Mar 07Apr 07May 07Jun 07Jul 07Aug 07Sep 07Oct 07Nov 07Dec 07Jan 08Feb 08Mar 08Apr 08May 08Jun 08Jul 08Aug 08Sep 08Oct 08TP (mg/L)Nov 08Dec 08Jan 09Feb 09Site 1 Site 2 Site 3 Site 4 Site 5Figure 3-12 TP Time Series, August 2006 to February 2009 (Source Council) 23.5.3 Catchment Rainfall Events (Plus Overtopping of TuckombilWeir)In addition to the catchment runoff discussed in the previous section, on occasions external runoff willenter the estuary via the Tuckombil weir/canal. Section 3.2.2 discusses the timing and predictedvolume of these overtopping events over the past several years. The catchment modelling whichwas completed (see Appendix D) identified the significant load contributions which may be input tothe estuary during these events. This is of course based on an assumed quality of water whichenters the estuary and it is recommended that further testing of influent waters should be conductedover time to refine these estimates.Given the large quantity of pollutants potentially entering the estuary, it would be expected that therewould be corresponding increases in pollutants measured within the estuary. The only period forwhich water quality data is available for an overtopping event, is for the event which occurred inJanuary 2008. As shown in Figure 3-11 and Figure 3-12 there were large responses in estuarinewater quality observed, most noticeable in the upper estuarine areas. Also, Figure 3-10 identifieshow the salt within the estuary is flushed out as a response to the large flood event.Hence, significant Richmond River overflows are likely to have a profound effect on water qualitywithin the Evans River, potentially more significant than catchment discharges alone to the estuary.3.6 Ecosystem Characteristics2Previous studies, such as the Estuary Processes Study (PBP, 1999a) which have reviewedecosystem characteristics, particularly, in-stream characteristics appear to have been largelydominated by conditions prior to and at the time of the contributing studies. The observation is madethat conditions within the Evans River at this time were likely to be significantly affected by theoperation of the fabridam on the Tuckombil Canal. The new fixed weir option is believed to providebetter water quality within the Evans River than the fabridam (M. Wood, Richmond River CountyThe zero (0) results are a function of the accuracy of the laboratory testing completed to derive the result. If the samplecontains less TN or TP less than was detectable by the laboratory procedure utilised, then this result has been recorded as0, although this is not strictly correct.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-21Council, Pers Comm, 2010), although, a comprehensive comparison of water quality conditions preandpost weir have not been undertaken as part of this study.Brief discussion in respect of key ecosystem components, including dominant in-stream and fringingvegetation and in-stream fauna has been provided. It should be noted that conditions are likely tohave changed as a result of the introduction of the Tuckombil weir. No discussion has been providedat this time in respect of terrestrial flora and fauna. It is expected that terrestrial flora and fauna wouldbe unlikely to be impacted by STP discharges to the estuary. The construction and operation of thewetland / forest (including pipelines) may impact on existing terrestrial communities depending onwhere it is sited and how it is operated. Further assessment of potential impacts and mitigationoptions for these communities would be completed once a preferred scheme and arrangement wasdeveloped.Seagrasses, Mangroves and Saltmarsh DistributionInformation prepared as part of the Comprehensive Coastal Assessment (NSW Dept. Of Planning,2007) included mapping of the distribution of seagrasses, mangroves and saltmarsh within theestuary as shown in Figure 3-13.This figure shows the seagrass beds within the estuary extend up to 7km from the entrance. Themost extensive beds exist within the first 4 kilometres of the entrance.Seagrasses can provide a number of valuable functions within estuaries such as processing ofnutrients, increasing dissolved oxygen, provision of food and or habitat, etc. Seagrasses can benegatively affected by excess turbidity within waterways which may be a result of suspendedsediments or even as a result of algae or other suspended matter. Other impacts can occur as aresult of changes in bed morphology which results in excessive velocities and scour of seagrassbeds. Other impacts can results from trampling and physical disturbances.This figure also identifies the locations of saltmarsh and mangrove along the estuary. It is noted thatextensive regions of saltmarsh and mangroves exist along the estuary from immediately west ofEvans Head to the commencement of the Tuckombil canal. Mangroves are generally hardy plantsbut can be affected by changes in the hydraulic and salinity regimes. Saltmarshes can also beaffected by changes to hydraulic and salinity regimes. Both saltmarsh and seagrass are sensitive tochanges in wave climate, such that may be induced by boating which affects bank stability.FishThe Evans River estuary supports a variety of estuarine fish species common to estuaries in theregion. The Estuary Processes Study (PBP, 1999a) includes details of a variety of fish andcrustacean species which were observed to have died during various water quality episodes withinthe estuary over the past 20 years. A brief summary of the primary causes of some of the moresignificant recorded fish kills are provided below:• March 1993 - This fish kill was associated with an acute discharge of acid sulfate soils runofffrom the Rocky Mouth Creek catchment. No barrier was present at the confluence of RockyMouth Creek and the Evans River at this time, which allowed highly acid water to drain fromRocky Mouth Creek into the upper reaches of the Evans River.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-23• March 1999 - this extensive fish and invertebrate kill was determined to be at least partlyattributable to acute oxygen depletion or anoxia. This may have been caused by water from theRocky Mouth Creek catchment entering the Evans River. The flood waters originated in theswamp areas of the Rocky Mouth Creek and water was retained there for more than a weekbecause of minor flooding in the Richmond River. The influent waters were determined to havea high biological oxygen demand as a result of biological decay of entrained organic materials.Chemical oxidation demand may have also been increased as a result of acid sulphate soilinteraction in this area as well.• Geolink et al (2008) reported a fish kill in 2001 as a result of a deoxygenation event when anoxicwaters entered the Evans River via Tuckombil Canal from Rocky Mouth Creek catchment andthe Mid Richmond. Geolink et al (2008) identified that a blackwater event (an event that cancontribute to the formation of anoxic conditions) did not result in a fish kill in the Evans River afterfloods in 2008. This was believed to be due to the weir preventing anoxic water from enteringthe Evans River from the Richmond River (M. Wood pers comm. 2008).Consistently, it can be seen from these examples, that the primary cause of fish kills in the EvansRiver was either acid sulphate soil runoff or organic rich runoff from the Rocky Mouth Creek orRichmond River catchment. These findings are consistent with the causes of fish kills in theRichmond River (WBM, 2006).It is understood that water quality conditions in the Evans River have significantly improved as aresult of the introduction of the fixed height weir in 2001 and has reduced the occurrence of fish killsin comparison to that happening in Rocky Mouth Creek / Richmond River (M. Wood, Richmond RiverCounty Council, Pers. Comm., 2010).As part of a site inspection of the Tuckombil Weir conducted in March. A minor fish kill was observedin Rocky Mouth Creek at the location of the fixed weir. Approximately 20 mullet were observed to befloating against the wall or bank on the southern extent of the Tuckombil Weir where it adjoins theembankment, as shown in Figure 3-14.Figure 3-14 Minor fish kill at Tuckombil Weir (March, 2010)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-243.7 Potential Ecosystem ResponsesThe introduction of non-saline STP effluent, containing relatively high concentrations of nutrients incomparison to background ambient conditions, into a mostly marine environment can impact waterquality and lead to associated biological / ecosystem responses. The following points identify someof the ecosystem responses that may occur:• Increases in nutrient concentrations can lead to changes in macroinvertebrate species. Certainmacroinvertebrate species are sensitive to increased nutrient concentrations and would beunlikely to be present in zones of the estuary experiencing lower water quality;• Increased nutrient concentrations can increase algal growth. Increased algal growth couldimpact on water quality through algal photosynthesis and respiration affecting diurnal dissolvedoxygen concentrations. Dieoff of algal blooms and associated bacterial decay could lead todeoxygenation of the water column potentially stressing fish and other benthic organisms.Excessive algal growth may increase water turbidity, reducing the depth to which light penetratesand hence impact on light dependent species, such as seagrass;• Settling of nutrient rich sediments may lead to nutrient rich sediments. Discharges of non-salineSTP effluent into saline environments may promote the flocculation of suspended materialcontained in the STP effluent. This flocculated material may settle to the bed of the estuary andcould potentially accumulate over time. If rates of nutrient release from the sediments is lessthan the rate at which new sediments are added, this may lead to an excess of nutrients formingin the sediments. The sediments over time could impact on the quality of surface water qualityby liberation of nutrients; and• Increased nutrient concentrations in the water column may promote growth of other waterdependent floral communities such as saltmarsh, mangrove and other littoral communities andassociated weeds.Significant changes in water and sediment quality as identified above, may lead to longer termbiological responses such as changes in the quantity and distribution of in-stream and littoral floralcommunities which would similar impacts on dependant fauna communities. Section 8.5 providesfurther discussion of the discharge schemes considered in relation to likely ecosystem responses.3.8 Social and Environmental ValuesA variety of social and environmental values were identified in the Estuary Management Study (WBM,2002). Values identified included:• Nature Conservation Values;• Cultural and Heritage Values;• Education and Scientific Values;• Scenic Values;• Recreation and Tourism Values;• Socio-Economic Values; and• Flood Mitigation Values.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-25Values which may potentially be affected by the proposed scheme have been discussed in furtherdetail in the following sections.Nature Conservation ValuesEstuarine habitats and ecology were identified as values of the Evans River. Habitats of value wereidentified in the lower estuary, including the deep hole (downstream of Iron Gates), the tidal channel,the transition zone between the tidal channel and the sand banks and the shallow tidal flats. Thesehabitats were identified as being of value for the habitat they provide to benthic fauna communities.Extensive areas of saltmarsh and mangrove were mapped along the length of the estuary, and somesmaller areas of the seagrass were also identified in the lower estuary. These areas also provideunique habitat and forage opportunities, not only to estuarine species, but for a variety of terrestrialspecies as well.The introduction of treated effluent from the STP has the potential to change water quality within theestuary, which may increase nutrient concentrations and in turn affect its trophic status.Education and Scientific ValuesThe estuary is considered to have educational values similar to other estuaries in the region. It isconsiderably smaller relative to some of the neighbouring estuaries such as the Clarence andRichmond River estuaries, which possibly present some benefits for use of the Evans River ineducational pursuits.In terms of scientific values, the Evans River estuary has contains a subfossil coral reef. The reef isreported (PBPB, 1999a) to exist approximately 9km upstream of the entrance (i.e. Doonbah locality).The reef is thought to have formed during periods of higher sea level approximately 120,000 yearsago, and is comprised of at least 20 scleractinian coral species (PBP, 1999a).The coral reefs were reported (PBP, 1999a) to be partly embedded in the mud bank in the intertidalzone. Bank erosion in this zone may impact on these coral fossils by eroding the bank materials inwhich they are contained.Scenic ValuesThe Estuary Management Study identified that, “The scenic qualities of the Evans Head area relate tothe foreshore and coastal reserves, proximity of Broadwater and Bundjalung National parks, low-keydevelopment and the ocean and waterway views from vantage points around the Evans Headvillage....The area’s natural vegetation combined with coastal headlands, sandy beaches (both smalland vast), wetland areas and a picturesque estuary form the basis of its appeal”.There is the potential that scenic values of the estuary, in term of consistent water colour andappearance could impacted in the immediately vicinity of the outfall, by the introduction of treatedeffluent from the STP via outfalls within the lower estuary. These considerations include:• The effluent stream would be a fresh water plume which would have positive buoyancy(compared to the surrounding, typically near ocean quality waters) and would tend to rise;G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-26• The STP effluent is typically less turbid than the water in the Evans River, which, combined withthe differences in density, will create a surface visual difference between the discharge and theambient water. Even with initial mixing resulting from the diffuser, the discharge will likely bevisible at least part of the time due to the turbidity and density differences between the effluentand Evans River water; and• The discharge plume might be visually apparent on occasion as a result of the momentum of thedischarge creating ripples on the surface of the water. Discharge velocities are likely to be toolow for this effect, however, at certain times, especially during periods of high discharge volume,low water surface elevation and still climatic conditions, this effect may be noticeable.As such there exists some potential for localised visual impacts, which while not detracting from thebroader scenic values of the estuary, may on occasions impact on scenic values in the vicinity of thedischarge.Recreation and Tourism ValuesThe Estuary management Study (WBM, 2002) identified that the main features of the Evans River inrespect of recreation and tourism values included the fact that the estuary provides:• “a range of opportunities for outdoor recreation (both land and water-based) in a natural setting;and• opportunities for the appreciation of the natural environment and cultural heritage”.The types of activities identified included “fishing, relaxing, picnics/barbecues, swimming, boating,walking/hiking, socialising, sightseeing and nature observation. The results of the coastal valuessurvey showed these to be the most popular activities, with about 70% of respondents indicating theyfish at the Evans River.”The introduction of treated effluent from the STP has the potential to affect people’s perceptions ofthe cleanliness and safety of undertaking recreation within the estuary. Activities most likely to beeffected are those involving swimming or fishing which include immersion in water or eating of catchor harvest from the estuary.Perception changes may lead onto other impacts, notably socio-economic impacts, particularly ifsuch perceptions lead to individuals making alternative decisions about where they choose to holidayor how they holiday. This may have significant ramifications for Evans Head which has an economygeared toward tourism. There is presently no commercial fishing or oystering within the estuary, sothese industries cannot be affected.Estuarine discharges of treated sewage are relatively common place in regional areas along theNSW North Coast. Generally most of these localities support successful tourism industries offeringsimilar recreational opportunities to that of Evans Head. The increasing focus of recreation relatedusage of estuaries is ‘raising the bar’ in terms of protecting relevant environmental values, and islikely to be contributing to more complex and costly estuarine discharge solutions being sought tominimise potential impacts on these values.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-27Water Quality ValuesThere were a number of water quality values documented in Section 2.6 for the Evans river estuary.A discussion of potential effects of discharges is provided below:• Protection of aquatic ecosystems – Existing water quality within the estuary, exceeds some ofthe guideline trigger values for nutrients, turbidity and chlorophyll-a. The exceedences werenoted to occur upstream of the confluence with Brandy Arm Creek in the upper estuary. Futuredischarges may further impact upon nutrient levels, potentially triggering adverse biological /ecosystem responses, e.g. an algal bloom.• Visual amenity – there may exist localised impacts on visual clarity and/or hue near thedischarge location. There are unlikely to be impacts on water reflectance, or the presence ofsurface films, debris, petrochemicals, algae, etc. There may be some detectable changes inodour in the immediate vicinity of the discharge, as a result of the surfacing of the buoyant STPplume and the presence of suitable climatic factors which move the odour towards sensitivereceptors.• Secondary contact recreation – The STP discharges will be highly treated and disinfected.Based on historical STP performance data for faecal coliforms, concentrations of faecal coliformsin the discharge would be unlikely to impact on secondary contact recreation water qualityvalues. No information on enterococci concentrations were however available, and these alsoform part of the applicable water quality values. Beachwatch data is presented in Section 2.6.1and it identifies periodic water quality issues within a monitoring location within the Evans River.No specific causes for these exceedences were identified. Further assessment of potentialimpacts of STP discharge on this value is required.• Primary contact recreation – as for secondary contact recreation. Further assessment ofpotential impacts of STP discharge on this value is required.• Consumption of aquatic foods (to be cooked prior to eating) – there is no commercial harvestingof fish or oysters within the Evans River estuary. However, there is recreational fishing andpotentially oyster harvesting within the estuary. It is unlikely that this value would be impactedupon due to the high levels of treated of STP effluent and the fact that it relates to cookedseafood which is likely to further sterilise food. The STP discharge may however influence theperceived health of harvested aquatic foods. Further assessment of potential impacts of STPdischarge on this value is required.Air Quality• Air quality is a value not previously identified for the estuary, but one which is likely to exist. It isstressed that odour impacts (if at all evident) are likely to be localised and occur under infrequentsets of tidal and climatic conditions. Examples of these conditions may include low tidal velocitieswhich allow the plume to more readily surface in combination with light winds.SummaryTable 3-2 presents social and environmental values of the Evans River estuary as outlined in thissection. The table provides a discussion of the value and how it may be pressured by the proposeddischarge and the construction of the wetland / forest and associated pipelines. Section 8.6 providesfurther discussion of the discharge schemes considered on these identified values.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-28Table 3-2Identified Values and Potential Pressures Resulting from the DischargeIdentifiedValueNatureConservationValuesCultural andHeritageValuesEducationandScientificValuesScenicValuesRecreationand TourismValuesCurrent Status of ValueHabitats of value for benthic faunacommunities include the deep hole(downstream of Iron Gates), the tidal channel,the transition zone between the tidal channeland the sand banks and the shallow tidal flats.Habitats of value for birds and fish includeextensive areas of saltmarsh and mangrove,and some smaller areas of the seagrass.The locations for the wetland / forest are notfixed and further assessment of values wouldneed to be assessed at the time of siting.Similar assessment of pipeline routes wouldbe required.Estuaries are a known food source forAustralian Aboriginals. There are likely to becultural values associated with the continued‘health’ of the river, to allow for these practicesto continue.The locations for the wetland / forest are notfixed and further assessment of values wouldneed to be assessed at the time of siting.Similar assessment of pipeline routes wouldbe required.The estuary has educational values similar toother estuaries in the region.Similarly, the estuary has scientific valuessimilar to other estuaries in the region,however, it is noted that the estuary containsa subfossil coral reef (which is reported toexist near Doonbah).The estuary links beaches, National Park andother natural areas around the township ofEvans Head, which itself is characterised bylow-rise coastal style developments.The waters of the estuary are a place forpassive and active recreation.The Evans River estuary has previously beenidentified to provide a range of outdoorrecreational opportunities. These have beenidentified to include, appreciation of thenatural environment and cultural heritage,fishing, relaxing, picnics/barbecues,swimming, boating, walking/hiking, socialising,sightseeing and nature observation.Pressure from DischargeIncreased loads of nutrients may alter thetrophic status of the estuary which in turn mayimpact on habitat and ecological values of theestuary.Construction of the wetland / forest, and/orrouting a pipeline to or from this site mayimpact on nature conservation values outsideof the estuary, e.g. significant vegetationareas, dedicated reserves, etc.As above.Also, there exists a variety of sites in theestuary which may have Aboriginal orEuropean cultural or heritage valuesassociated with them. These may be sacredsites or existing structures, etc. These sitesmay be impacted upon by the construction ofa wetland / forest, or routing a pipeline to orfrom this site.Construction of the wetland / forest, and/orrouting a pipeline to or from this site mayimpact on the subfossil reef.Localised impacts from STP discharge plumemay occur as a result of the STP dischargebeing less turbid than surrounding water at thedischarge site. Also there may be a noticeableripple on the surface of the estuary at certaintimes as a result of the discharge.The location of the future wetland / forest ifultimately selected, may impact on existingscenic areas.The introduction of STP effluent may degradeexisting values (e.g. visual, scenic, etc) or bebelieved to be degrading values (i.e.perception).Socio-EconomicValuesFloodMitigationValuesThe township of Evans Head benefits fromtourism. Tourism is likely to contribute to orsupport certain local industries, e.g.accommodation, retail, etc.The estuary floods periodically as a result ofinputs from external catchments, the EvansRiver provides some flood mitigation values tothe external catchment.Related to perceived or actual impacts onother estuary values, such as recreation andtourism values.None identified by introduction of STP effluentAir Quality Air quality is likely to be a value. STP discharges to the estuary may impact onair quality.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-293.9 Summary of ProcessesIn broad terms it appears that:• Entrance conditions are in a form of dynamic equilibrium with a net inflow of sand during drierperiods and erosion occurring during flood periods. Further investigations would be required tobetter quantify sediment budgets in this zone and identify if there is any net change in shoaling inthe lower estuary;• Catchment inputs are relatively low (in comparison to many other estuarine catchments) due tothe largely forested state of the catchment. Of concern are the agricultural discharges anddischarges from the Brandy Arm Creek at the upper end the estuary which has experienced ahistory of poor water quality. Also overflows from the Rocky Mouth Creek and Richmond Rivercan significantly affect estuarine hydrodynamics and water quality;• Tides constitute one of the key driving processes of the Evans estuary and dominate estuarinehydrodynamics during dry weather periods. Flooding has been observed to dominate estuaryhydrodynamics on occasions such as for the large flood event of early 2008. Tidal rangesdecrease with increasing distance from the ocean to where Brandy Arm Creek meets the EvansRiver, as a result of hydraulic losses associated with bed friction (i.e. water crossing the bar,entrance shoals, etc), constriction through the Iron Gates and sinuosity of the river between IronGates and Doonbah. The upper sections of the estuary between Brandy Arm Creek confluenceand Tuckombil canal appear to be hydraulically efficient and there is no significant reduction intidal ranges through this zone. Tidal phasing (i.e. difference in timing between slack tides andpeak discharges) is evident in the river and will need to be taken in account in developing ebbtiderelease scenarios. Tidal flushing increase from less than 3 days in the lower estuary (up toIron Gates) up to greater than 70 days at the far upstream end of the estuary.• In terms of fluvial sedimentary processes, active accretion is likely to be occurring between IronGates and the Elm Street Bridge, although the rate may be quite small. This sediment is likely tobe sourced from the erosion of riverbanks and bed between Brandy Arm Creek and Iron Gates.This indicates that tidal hydrodynamics may continue to alter upstream of the Iron Gates until astable river form is achieved. The lower estuarine hydrodynamics will be influenced by entranceconditions such as the entrance shoal and bar, however, these systems are reported to bedynamically stable.• Water quality in the estuary generally exhibits a near linear trend from near oceanic water qualityconditions at the downstream end to a condition more defined by catchment inflows at the upperend. The linear trend along the estuary during periods of dry weather is governed by the tideand during periods of low catchment flows, upstream water quality conditions can (during thesetimes) be very good and comply with accepted guideline trigger values. However, during periodsof catchment inflows water quality conditions can decrease throughout the estuary, but mostnoticeably at the upper end of the estuary which has had a history of poor water quality.• Hence, when considered on an annual median basis, sites in the upper reaches of the estuary(i.e. Sites 1 and 2) do not achieve all of the DECCW and ANZECC annual median guidelinetrigger values for chlorophyll-a, TN, TP and turbidity. Water quality conditions at sites 3, 4 and 5are generally much better and consistently achieve the guideline trigger values (see Figure2-20). Trigger values for primary and secondary contact recreation were achieved at all sitesduring dry weather periods, with high faecal coliform counts observed in the estuary after rainfallG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REVIEW OF ESTUARY PROCESSES 3-30events. This is typical of many estuaries in the North Coast region. The upper end of thecatchment is susceptible to inflows from the Rocky Mouth Creek/Richmond River, WoodburnDrain and Brandy Arm Creek.• There is a risk that some identified values of the Evans River estuary may be affected by theproposed discharges. These mostly relate to potential water quality impacts, and the publicperception of these discharges on people’s ability to recreate with and consume and harvestfood from the estuary.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CATCHMENT MODELLING 4-14 CATCHMENT MODELLINGThis section of the report outlines the catchment modelling which was completed by BMT WBM. Thecatchment modelling was completed as a key component of the study to provide details of flows tothe Evans River. This information was used in the establishment of the hydrodynamic and advectiondispersionmodels outlined in Section 6.It is noted that catchment modelling results are uncalibrated because there are no monitoringsystems or programs for either flow or water quality on any of the individual catchments.It is believed appropriate for uncalibrated flow inputs to be utilised by the AD model because itscalibration focuses primarily on the recovery of salinity within the estuary after a rainfall runoff eventflushes saline water entirely, or almost entirely, from the system. Recovery of salinity in the estuary isa function of tidal dynamics, not the size of catchment inflows and as such the model uncertaintyassociated with those inflows.Catchment pollutant load estimates were developed, but not used as inputs to the advectiondispersionmodel. Summary of the catchment pollutant modelling is included in Appendix D.Catchment pollutant load results were not included in the advection-dispersion modelling for thefollowing reasons:• As discussed in Sections 3.5.2 and 3.5.3, pollutant loads typically increase during storm events.Using uncalibrated pollutant loads as inputs to the calibration of the advection-dispersion (AD)model and discharge scenario assessments would introduce an unquantifiable uncertainty to theoverall model results;• Pollutant loads do not affect the AD model calibration because the calibration parameter issalinity and the identified pollutants do not affect salinity; and• Pollutant loads in the discharge scenario assessments are evaluated as a result of the STPdischarge in relation to background concentrations. While background concentrations are afunction of catchment loads, the contribution of individual catchments to the overall water qualityof the Evans River cannot be determined at this time.4.1 WaterCAST Catchment Modelling FrameworkThe WaterCAST modelling framework (Argent et al 2008a, 2008b) provides the ability to simulatecurrent catchment characteristics and responses, in addition to evaluating the impacts of land usechange and the implementation of best management practices. The WaterCAST framework is notone model, but a framework in which groups of different models can be selected and linked such thatthe most suitable model to describe a particular aspect of the catchment can be used.Appendix C contains an overview of the process which is typically applied in constructing aWaterCAST model.4.1.1 Data Requirements for a WaterCAST ModelThe WaterCAST modelling framework requires a number of data sets as outlined in the modelbuilding steps (discussed in Appendix C). These key data sets include:G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CATCHMENT MODELLING 4-2• A digital elevation model (DEM) for subcatchment delineation;• A land use map to provide a basis for functional unit definitions;• Climate data (daily rainfall and evaporation data);• Water quality data and/or Event Mean Concentration (EMC) / Dry Weather Concentration (DWC)data for pollutant export model parameterisation (if available);• Hydrologic data for model calibration (if available); and• Point source (e.g. wastewater treatment plant) flow and water quality data.Section 4.2 details the data sets used to create the Evans River WaterCAST model.4.2 Evans River WaterCAST Input DataThe following section summarises the data used to construct the Evans River WaterCAST modelincluding:• Subcatchment Map;• Land use;• Climate;• Hydrology;• Water Storages and Point Sources; and• Water Quality.4.2.1 Subcatchment MapA subcatchment map for the Evans River was developed using a combination of methods. Due tothe spread out nature of the available data, a number of Digital Elevation Models (DEM) werepatched together to create the subcatchment map. DEM data used included:• Airborne Laser Scan (ALS) data provided by Council;• Photogrammetric and ALS survey compiled for the Richmond River Flood Mapping Study (BMTWBM, 2010). Data for this study has been previously supplied by local Councils and the NSWRoads and Traffic Authority for the following projects:‣ Ballina Flood Study Update (BMT WBM, 2008);‣ Casino Floodplain Risk Management Study (WBM Oceanics, 2001);‣ Tuckombil Canal Flood Affect Assessment (WBM Oceanics, 2005);‣ Wardell and Cabbage Tree Island Floodplain Management Study (Patterson Britton, 2004);‣ Lismore Floodplain Management Study (Patterson Britton, 2001); and‣ Woodburn to Ballina Pacific Highway Upgrade (Brown Consulting, 2006).Minor adjustments were made to this subcatchment map to ensure that catchments outputscorresponded to input locations within the hydrodynamic model. The resultant subcatchment mapcontains 30 subcatchments and is shown in Figure 4-1.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CATCHMENT MODELLING 4-44.2.2 Land UseLand use data for the Evans River catchment was obtained from NSW Department of Environment,Climate Change and Water (September 2009), supplied by Hydrosphere Consulting. Using the NSWLand Use Mapping Program (LUMAP) codes, this data contains over 500 detailed land use classeswhich are grouped under 14 major categories. This data was modified from the original to reduce thetotal number of land uses (Functional Units) to 10 based on similar hydrological configurations for theregion. The data reclassification is shown in Table 4-1. Total areas for each land use are shown inTable 4-2. The land use map used in the WaterCAST model is shown in Figure 4-2.Table 4-1Functional Units Used in WaterCAST Based on Land Use TypeFunctional Unit Major Land use Category Detailed Land use ClassNational parkConservation AreaPrivate conservation agreementState forestTree lotSpecial CategoryForeshore protection - vegetated fore dune (coastal feature)Hardwood plantationNative forestNative forest - regenerationTree & Shrub CoverNative woody shrubForestSoftwood plantationTree lot - exotic speciesWindbreak or tree corridorUrbanUrban recreationFloodplain swampFloodplain swamp - back swampWetlandFloodplain swamp - billabongMangroveMudflatGrazingGrazingSwampDegraded land (salt site, eroded area)GrazingRecently cleared landSown, improved perennial pasturesSown, improved perennial pasturesHorticulture HorticultureVolunteer, naturalised, native or improved pasturesBuilding associated with horticultural industryNurseryOrchard - tree fruitsOrchard - tree fruits - irrigatedPecan, macadamia and other nutsShade house or glass house (includes hydroponic use)Tea Tree PlantationTea Tree Plantation - irrigatedCroppingCropping - continuous or rotationIntensive Animal ProductionHorse stud and/or horse breeding facilitiesIntensive animal production - poultryMining & QuarryingDerelict mining landMine sitePower GenerationQuarryElectricity substationEnergy corridorIntensive Use Special CategoryFarm InfrastructureTransport & Other CorridorsAerodrome/airportCommunications facilityUrbanAbandoned urban or industrial areaIndustrial/commercialLandfill (garbage)SawmillSewage disposal pondsSurf club and/or coastal car parking facilitiesG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CATCHMENT MODELLING 4-5Functional Unit Major Land use Category Detailed Land use ClassRoadRural ResidentialTransport & Other CorridorsUrbanRoad or road reserveAlternate life style community under multiple occupancyCemeteryRural residentialSmall to medium forested or wilderness blocks with isolatedresidential buildings.Sugar CaneUrbanCroppingUrbanSugar caneArea recently under development for urban, commercial and/orindustrial usesCaravan park or mobile home villageGovernment and private facilitiesResidentialWaterRiver & Drainage SystemSurf club and/or coastal car parking facilitiesAquacultureDrainage channelDrainage depression in cropping paddockDrainage or water supply channelFarm damIrrigation damIrrigation supply channelMarinaPrior streamRiver, creek or other incised drainage featureSpecial CategoryWater supply pressure reservoir including water filtration plantBeachCliff/rock outcropSand spit/estuarine sand islandWetlandFloodplain swamp - billabongTable 4-2Land Use Area BreakdownFunctional Unit NameCurrent Land useArea (ha) Percentage of Total (%)Forest 7,123 75.1%Grazing 1,084 11.4%Horticulture 5 0.1%Intensive Use 290 3.1%Road 43 0.5%Rural Residential 390 4.1%Sugar Cane 133 1.4%Urban 174 1.8%Water 246 2.6%Total 9,488 100.1%G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CATCHMENT MODELLING 4-74.2.3 Rainfall and Evapo-transpirationRainfall and potential evapo-transpiration (PET) data imported to the WaterCAST model domain isprocessed to produce a single time-series for each subcatchment.Daily rainfall data for the WaterCAST model was sourced from the Bureau of Meteorology’s EvansHead RAAF Bombing Range rainfall station (58212) for the period 1 st January 2000 to 28 th February2010. Potential evapotranspiration data was sourced from the Bureau of Meteorology (BOM) PETatlas (BOM, 2009) which provides mean monthly data on a 10km x 10 km grid across all of Australia.4.2.4 HydrologyThe Evans River WaterCAST model has been parameterised using the SIMHYD rainfall-runoffmodel. No stream gauge data was available to estimate hydrologic parameters. Thereforeparameterisation of the catchment model was based on the study by Chiew and Siriwardena (2005).This study provides guidance on estimating SIMHYD parameters in ungauged catchments. Theestimation is based on a number of regional factors including:• Mean annual rainfall;• Mean annual areal potential evapotranspiration; and• 10 th and 90 th percentile elevation.The following factors were then determined using McKenzie et al (2000), Western and McKenzie.(2006) and the Digital Atlas of Australian Soils:• Fraction of total native woody vegetation;• Plant available water holding capacity;• Soil depth and hydraulic saturation; and• Soil transmissivity.These factors were then used in the formulas provided in Chiew and Siriwardena (2005) to determine5 of the 9 SIMHYD parameters including:• Baseflow Coefficient;• Interflow Coefficient;• Rainfall Interception Storage Capacity;• Recharge Coefficient; and• Soil Moisture Storage Capacity.Pervious fraction values were modified to reflect the relative impervious areas of Roads (35%pervious), Urban (65%), Intensive Use (35%) and Rural Residential (90%). Default values for theimpervious threshold, infiltration coefficient and infiltration shape were used.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CATCHMENT MODELLING 4-84.2.5 Water Storages and Point SourcesWater StoragesThe Evans River WaterCAST model contains no water storages.Tuckombil CanalThe Tuckombil Canal provides an additional flow path for floodwaters within the Richmond Rivercatchments to escape to the ocean via the Evans River, thereby alleviating flood levels andinundation periods in the areas to the west and around Woodburn. This is an important inclusion inthe catchment model for periods of high flow.The Tuckombil Canal represents the upstream boundary of the catchment model, and therefore atime series of inflows from the canal has been incorporated into the model. This time series wasdeveloped based on data provided by Manly Hydraulics Laboratory for tide level recorders principallyat the Tuckombil Canal Weir and at Rocky Mouth Creek and is shown in Figure 2-12. There is a totalof 110 days of flow over the Tuckombil Canal weir between the 1 st January 2000 and 28 th February2010.Figure 4-3Tuckombil Canal Inflow Time SeriesSewage Treatment PlantThe Evans River WaterCAST model contains no STP inflows. The Evans Head STP currentlydischarges to Salty Lagoon, which is outside the catchment area of the Evans River.4.3 Model ResultsThe final Evans River WaterCAST model layout is shown in Figure 4-4. Within the WaterCASTmodel estimated flows and constituent loads can be extracted at any node, link or subcatchment inthe model domain. Key model outputs presented for the existing case scenario include:• Estimated mean annual flows and constituent loads;G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CATCHMENT MODELLING 4-9• Estimated mean annual land use constituent loads (kg/ha/yr); and• Temporal variability in flows and constituent loads.Note details of load exports have been included in Appendix D.Figure 4-4Evans River WaterCAST Model4.3.1 Estimated Total and Mean Annual FlowsModelled total flows over the period January 2000 to December 2009 are provided in Table 4-3. Thistable shows total flows from the Evans River catchment with and without the inclusion of theTuckombil Canal inflows.Table 4-3Estimated Total Flows from Evans River and via Tuckombil CanalSourceFlowML PercentEvans River Catchment Flows 406,000 51%Tuckombil Canal Inflows 387,000 49%Total Outflow 793,000 100%G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CATCHMENT MODELLING 4-104.3.2 Estimated Mean Annual Land Use FlowsModelled mean annual runoff flows and percentage of overall flows from each land use are presentedin Table 4-4.Table 4-4Mean Annual Flows by Land UseLand UseFlowML/yr PercentForest 26,270 65%Grazing 4,010 10%Horticulture 20 0%Intensive Use 2,840 7%Road 420 1%Rural Residential 1,810 4%Sugar Cane 490 1%Urban 1,210 3%Water 3,520 9%Total 40,6104.3.3 Temporal RepresentationModelled annual flows as delivered from the Evans River Catchment and Tuckombil Canal areprovided in Table 4-5. This table also shows the total and mean annual flows from the Evans Rivercatchment. This data includes the Tuckombil Canal inflows.Table 4-5Estimated Total Annual and Mean Flows from Evans River Catchment andTuckombil Canal (2000 –2009)YearFlow (ML)Evans River Catchment Tuckombil Canal2000 20,900 2002001 46,800 78,8002002 11,800 1002003 38,500 2002004 26,000 9,6002005 46,800 29,3002006 55,300 23,5002007 27,900 2002008 57,200 42,4002009 74,700 203,000Total 406,000 387,000Mean Annual 40,600 38,700Figure 4-5 shows the estimated total annual flows from the Evans River catchment. Estimations ofcatchment pollutant exports of TSS, TN and TP are included in Appendix D.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CATCHMENT MODELLING 4-11300,000250,000Evans River Catchment Tuckombil Canal Rainfall2,5002,000ML/Year200,000150,000100,00050,0001,5001,000500Rainfall (mm)‐2000 2001 2002 2003 2004 2005 2006 2007 2008 2009Year‐Figure 4-5Estimated Annual Flows4.3.4 Results SummaryThe WaterCAST model has been developed using available data. As previously mentioned, limitedflow and water quality data is available to make an accurate prediction of flows and pollutant loadsfrom the catchment. Flows presented in this section are suitable for use in this study, taking intoconsiderations its limitations.As can be seen in Figure 4-5, a large proportion of flows discharging from Evans River, particularly in2001 and 2009, enter upstream as inflows from Tuckombil Canal. These modelled flows are highlyvariable from year to year and are dependent on large rainfall events and Tuckombil Canal inflows.Further discussion on pollutant loads is included in Appendix D. In summary, these assessmentsidentified a high variability in annual pollutant loads. Higher loads corresponded to higher runoffyears indicating a higher proportion of event based runoff (and associated pollutant load) rather thanbase flows during these years. The majority of suspended solid loads are attributed to the TuckombilCanal inflows through most years. Total nitrogen loads, on the other hand, are associated with runofffrom the surrounding catchment. The majority of total phosphorous loads are associated with runofffrom the surrounding catchment in all years except for 2001 and 2009 where large Tuckombil Canalinflows result in a significant increase in TP loads. The contribution of the forest and grazing lands tothe overall constituent loads coming from the study catchment area is evident (excluding TuckombilCanal). However, when based on area, sugar cane, road and intensive land uses contributesignificantly to pollutant loads.The limitations of the model (i.e. inability to use locally specific data for the purposes of calibration)could be reduced by:• Catchment specific event load monitoring, for individual land use classes, would provide betterpollutant export load predictions within the catchment, however, given the variability noted withinthe report, this would have to be collected over an extended period in order to derive suitable,G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CATCHMENT MODELLING 4-12locally applicable parameters. Undertaking this action would improve adopted dry and wetweather pollutant export coefficients for various land uses within the WaterCAST model toprovide better predictions of loads.• A flow gauge monitoring stations should be installed to collect daily flows within natural and/orurbanised parts of the catchment. This would allow calibration of the hydrology components ofthe WaterCAST model to provide better predicted flows and loads.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-15 WETLAND AND CARBON SEQUESTRATION MODELLINGThis section documents the preliminary assessment of wet weather discharge to the Evans Riverfrom a potential wetland based effluent management system. For the purpose of this preliminaryassessment, the wetland effluent management system was based on the concept developed by TheWater and Carbon Group (WCG) in a feasibility report (WCG, 2009) prepared for Council. Itincorporates a free water surface wetland for effluent polishing with effluent irrigation of a 125 hawetland forest intended to be operated for carbon sequestration.Following an initial review of the modelling process adopted in WCG (2009), a methodology wasdeveloped to undertake a more detailed and dynamic mass balance modelling process to provide arepresentative time series for the RMA modelling. Daily time series of hydraulic, nutrient andpathogenic indicator loads discharging to the Evans River from the wetland forest were derived.Provided in this section is a summary of the review of WCG (2009) modelling, a description of thepreliminary concept developed for this assessment, the methodology and input data used inmodelling and a summary of key results.5.1 Peer Review of Water and Carbon Group ModelsAn initial review of the modelling completed by WCG (2009) was completed to ascertain the degreeto which the models could be re-established for use in the preliminary assessment. The reviewinvolved a critical assessment of the tools, input data and design concept to determine the suitabilityfor this project. It also involved consideration of alternative approaches to wetland / forest modelling.5.1.1 Free Water Surface Wetland Treatment PerformanceThe volumetric empirical model developed by Reed et al (1995) was adopted by WCG for estimationof treatment performance for the 15 ha wetland. This model is one of two recognised methods for thedesign of wastewater treatment wetlands, which assume plug flow hydraulics and utilise empiricaldata to apply first order decay to pollutant inputs based on observed long-term performance of otherwastewater wetlands. The alternative model (developed by Kadlec and Knight) adopts a similar blackbox approach, but uses an areal rather than volumetric basis. BMT WBM support the use of thevolumetric Reed model for this wetland design process as it allows use of performance data from theWest Byron STP (relatively local example). Areal models do not allow application of performancedata to develop decays rates unless wetlands have the same surface area.WCG suggest that the model has been calibrated to some degree to the West Byron STP wetland.In effect, average outlet concentrations from the West Byron wetland have been put forward as C*values (background concentrations). While the West Byron STP effluent is similar to Evans Head,there are some differences. Nitrogen concentrations are substantially higher based on recentperformance data for Evans STP. Total phosphorus is also higher in concentration at West ByronSTP. Other parameters do generally align with West Byron performance and as a result can beconsidered acceptable C* values. Following this review, BMT WBM decided to test the application ofWest Byron wetland decay rates to Evans Head STP effluent.In reporting TN effluent concentration from the wetland as the sum of ammonium and nitrate, WCGare ignoring the significant organic-N concentrations typically observed in wetland effluent. Organic-G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-2N constitutes greater than 90% of Total Nitrogen (TN) at West Byron (Australian Wetlands, 2006).When including Organic-N, TN in wetland effluent is unlikely to consistently meet ANZECC Low RiskTrigger values.WCG adopted the default Reed et al (1995) rate constants for wetland treatment modelling. It isworthwhile to compare approximate rate constants for the Byron West STP wetland against thesedefault values (based on a large number of wetlands from the USA). Even if the West Byron valuesare not adopted, they will assist in gauging the level of conservatism applied to wetland performanceat this preliminary stage.Based on the outcomes of this review, monitoring data and design information from West Byron STPwas sourced from Byron Shire Council to assist in determining C* values and rate constants. Thisinformation was also used to establish an appropriate breakdown of nitrogen species.5.1.2 Wetland Carbon Forest and Wetland HydrologyWCG utilised Model for Effluent Disposal by Land Irrigation (MEDLI – Gardner and Davis, 1998) toassess the water balance of the proposed wetland carbon forest and the treatment wetland. Adescription of this model is provided in Section 5.3.1.2. MEDLI does represent the mostsophisticated Australian mass balance model for simulating water and nutrient dynamics in aneffluent irrigation scheme and is used regularly by BMT WBM. The specific application in this case isnot typical in that it is not true irrigation of a productive crop, pasture or forest. The use of MEDLI tosimulate a wetland forest requires a comprehensive understanding of MEDLI algorithms and structureto ensure results are representative.The WCG MEDLI model was re-established by BMT WBM and reviewed to determine suitability forthe purpose. Consideration was also given to the potential to use alternative models / tools toimprove the robustness of outputs. In particular, the potential to use components of the CSIROWATLOAD and WATSKED models (Myers et al, 1999) was considered. These models weredeveloped specifically to assess effluent irrigated forestry plantations and are based on years of fieldmonitoring and research. Despite the models operating on a monthly time step, BMT WBMinvestigated the potential to use the algorithms and experimentally derive input parameters (specificto effluent irrigated forests) for this project. These resources were not considered appropriate for thisproject for a number of reasons.• Forest specific data was primarily derived for dry forest species in arid and temperate zones;• Effluent nutrient concentrations were consistently higher (resulting in different growth responses);and• Irrigation was always undertaken using a deficit approach with soils maintained below fieldcapacity.Following a review of available tools, it was determined that MEDLI remained the most appropriatetool to use for modelling water balance dynamics for the wetland and forest.Notwithstanding, there are a number of limitations to the use of MEDLI to simulate the forest thatmust be addressed. Some of these limitations have been largely overcome as part of the preliminaryassessment but others will require further consideration if this discharge option is considered feasible.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-3The WCG MEDLI modelling was undertaken as a rapid, water balance assessment and did notacknowledge or address some of these issues:• WCG were instructed by Council to adopt a single average daily flow rate for STP inflows alongwith the “Average” infiltration/inflow function within MEDLI resulted in a conservative inflow timeseries (as shown in Figure 5-5). In particular, the significantly higher peak flow events during wetweather have the potential to alter discharge volumes and subsequent pollutant loads to EvansRiver;• WCG have used the Pond module of MEDLI to simulate the hydraulic performance of thetreatment wetland by adopting parameter values that best represent surface area andoperational volume of the wetland. The effective surface area and maximum storage volumeand minimum drawdown are sufficiently representative of how the wetland would operate andallow for a minimum (void adjusted) depth that ensures treatment would occur at all times;• Soil parameters adopted for the WCG modelling were reported to be based on the Dungarubbalandscape (Morand, 2001). While soil water storage parameters were within expected ranges,soil depths and limiting Saturated Hydraulic Conductivity (SHC) were not representative of typicalsoils and landscapes along the Evans River.By adoption of very large soil horizon depths (a total soil depth of 2.15m was assumed), PlantAvailable Water Capacity (PAWC), Field Capacity (FC) and Saturated Water Content (SWC) areoverestimated where groundwater is shallow. For a large part of the study area, the watertablewill be within this ~2m depth, making part of this depth unavailable for storage and effectivelyraising the point of discharge out of the MEDLI model. This results in overestimated evapotranspirationand underestimated deep drainage.A limiting SHC of ~0.015mm/hr was adopted by WCG (approximation due to rounding of value inMEDLI summary file supplied in WCG report). This value is very low and BMT WBM can onlyassume it was adopted in an attempt to represent the hydraulic limitation placed on deepdrainage by the higher watertable. The limiting SHC equates to 0.00036 m/day and results insignificantly lower than typical groundwater velocities even for low lying estuarine environments.The impact of this low value is a substantial reduction in deep drainage (i.e. groundwaterrecharge) and overestimate of surface runoff. While some deep drainage may re-surface atlower points within a forest site, this re-surfacing water is likely to reinfiltrate following a rain eventas the watertable subsides to long-term levels;• Gardner and Davis (1998) recommend adoption of the ‘Monthly Covers’ plant module whensimulating a forest / tree plantation where parameters for dynamic plant growth are not known.This option was selected by WCG for their modelling and a constant monthly cover of 70% wasselected. While this option allows simulation of soil evaporation and plant transpiration, MEDLIdoes not calculate biomass growth or nutrient uptake. As a result no understanding of soilnutrient dynamics can be obtained from the WCG model; and• Nutrient dynamics have been simplified in the WCG assessment to an assumption that theconcentration of runoff from the wetland forest would be roughly equivalent to treatment wetlandeffluent quality, which is at or near (ignoring organic-N) ANZECC Low Risk Trigger Values forLowland Rivers in South East Australia. This is unlikely to be the case and WCG have notaddressed the primary influence, such that an effluent management system would have on a siteG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-4which is a significant change in hydrology (higher runoff and deep drainage resulting in greatermobilisation of background nutrient sources within the wetland).The outcomes of this review have been used to refine and enhance modelling procedures for thispreliminary assessment. Further detail on how the above issues were addressed is provided in thesubsequent sections.5.2 Preliminary Concept for ModellingFor this preliminary assessment, the effluent management concept summarised in the WCGFeasibility Assessment (2009) has been largely retained for impact assessment. Critical assumptionsregarding site and soil characteristics have been refined through short-listing of four indicativelocations for a wetland / carbon forest effluent management system. These sites are hypotheticaland BMT WBM understands no investigations have taken place at this stage to determine suitabilityor landholder interest. They provide a good representation of the likely landscapes within which sucha system would be located should it be determined feasible.The proposed effluent management system would involve the following components.• Conveyance of treated effluent from the Evans Head STP to a site adjacent to the Evans River;• Discharge to a (approx.) 15 ha free surface water wetland for effluent polishing;• Irrigation (currently assumed to be flood irrigation) of a bunded (approx.) 125 ha wetland forestwith controlled overflow into a continuous discharge system to the Evans River. The forestwould be planted with a mixture of local tree species suited to the floodplain / wetlandenvironment; and• Wet weather overflow from the treatment wetland is currently assumed to bypass the wetlandforest and connect with the discharge system to Evans River from the forest. However, given therelatively infrequent occurrence of wetland overflow (twice in the 53 year MEDLI modellingperiod), overflow from the wetland could conceivably discharge to the wetland forest.A schematic of the wetland / forest effluent management concept is shown in Figure 5-1. Thisconcept was used to develop the mathematical models of the wetland forest system for preliminaryassessment. Further information is provided in WCG (2009).5.3 Methodology and Data InputDevelopment of a time series of wet weather discharge to the Evans River from a wetland / forestsystem involved three primary activities:1 Average annual estimation of effluent quality and daily water balance modelling of the 15 ha freesurface water treatment wetland;2 Daily water, nutrient and pathogen mass balance modelling of the wetland forest to estimate riverdischarge volumes and pollutant dynamics in the forest; and3 Development of a daily time series of river discharge volumes and nutrient/pathogenic indicatorloads from both the treatment wetland and forest.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-5Information obtained through desktop assessment was used to develop a mathematical model of thesystem.Figure 5-1Indicative Wetland / forest Effluent Management Concept used for Modelling5.3.1 Models UsedAs discussed in Section 5.1, the Reed wetland model, MEDLI and the Decentralised Sewage Model(DSM) have been used for the preliminary assessment and represent current best practice in longtermperformance modelling of effluent polishing wetlands and irrigation schemes.5.3.1.1 Reed Free Water Surface Wetland ModelThe wastewater wetland process design model developed by Reed et al (1995) is recognised(DLWC, 1998) as one of two key tools that can be used to size treatment wetlands or estimate theperformance of existing wetlands. As discussed in Section 5.1, the Reed model is considered themost suitable for the current project. The Reed model treats a wetland as an attached growthbiological reactor and uses first-order plug flow kinetic equations to estimate removal of wastewaterconstituents. Reed et al (1995) developed rate constants for municipal effluent using performancedata from a range of wetlands in the USA. The model allows for adoption of site specific rateconstants and is readily transferable given its basis is wetland Hydraulic Retention Time (HRT) whichcan be determined irrespective of wetland configuration and surface area. Further information on theReed model can be obtained from DLWC (1998) and Crites et al (2006).5.3.1.2 MEDLIModel for Effluent Disposal using Land Irrigation (MEDLI) is a water and nutrient mass balance modeldeveloped by the Queensland Department of Natural Resources and Mines (now DERM) and theG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-6CRC for Waste Management and Pollution Control (Gardner and Davis, 1998). It is capable ofsimulating storage pond dynamics, irrigation scheduling, plant growth, transpiration and nutrientuptake, soil water and nutrient dynamics and salinity on a daily time step over long periods (up to 100years). The structure of MEDLI is shown in Figure 5-2.Figure 5-2Structure of MEDLI (Source: MEDLI Technical Description, Queensland DNR)The MEDLI Technical Manual (Gardner and Davis, 1998) provides a comprehensive description ofthe algorithms and modules of MEDLI.5.3.1.3 Decentralised Sewage Model (DSM)The Decentralised Sewage Model (DSM) is a GIS based decision support tool designed to assessand compare a range of wastewater servicing options from on-site sewage management toconventional gravity sewerage with central treatment and reuse/disposal. The DSM was developedjointly by BMT WBM and Whitehead & Associates Environmental Consultants. It has the capacity torapidly assess the long-term environmental/human health performance of wastewater systems inaddition to assisting in the concept design and costing of various servicing options. The DSM iscomprised of five modules as described in Figure 5-3. Each module of the DSM is able to be used inisolation or collectively depending on the needs of the project.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-7On-lot Performance Model (OLPM); simulates the performance of individual wastewater discharges to landapplication systems at a daily timestep. Hydraulic, nutrient and pathogen dynamics within the land application systemare modelled with daily surplus loads surcharging to the ground surface and discharging below the rootzone recordedas model outputs.Particle Tracking Model (PTM); tracks the flow path from individual wastewater systems to receiving waters of surplussurface (and shallow subsurface) hydraulic, nutrient and pathogen loads calculated using the OLPM. A user definedpollutant decay rate can be applied to the PTM where suitable data are available. The PTM assists in identifying likelyhotspots for sewage pollution and assessing the feasibility of gravity reticulation for community wastewatermanagement.Node-Link Model (NLM); allows the OLPM outputs for individual wastewater systems to be grouped into ManagementUnits (MU). MU’s may be based on physical subcatchments (e.g. for the purpose of input of data into a catchment model)or user defined groups (e.g. for the purpose of scenario testing or concept design of community wastewater systems).Grouped OLPM outputs are linked to a downstream model component such as a pump station, central treatment system,reuse/disposal facility or discharge to a receiving water. The NLM also allows treated effluent from central managementcomponents to be linked back to MU’s for reuse (e.g. to simulate dual reticulation).Central Management Components (CMC); simulate the operation of pump stations or central treatment, disposaland/or reuse systems. The CMC uses similar algorithms to the OLPM to simulate hydraulic, nutrient and pathogenprocesses.Costing Model (CM); estimates the capital and operating costs of the modelled wastewater servicing scenarios fromon-lot to central components. The CM utilises inputs from the NLM to define unit costs for elements of the CMC.Figure 5-3Summary of the Structure of the DSMFor this project, only the pathogen model from the Central Management Component (CMC) modulewas used in conjunction with MEDLI. The DSM uses the equations developed by Powelson andGerba (1994) as the basis for estimating viral adsorption and dieoff in unsaturated and saturated flowthrough soil. Effluent virus concentration, soil moisture dynamics (i.e. residence time), temperatureand soil characteristics are the most influential factors in the rate of viral dieoff. Validated modelsexist for simulating the first three of these four factors that use a first order decay equation torepresent viral die-off.5.3.2 Development of Indicative Site CharacteristicsFour indicative sites have been selected to test the feasibility of a wetland / forest effluentmanagement system as shown in Figure 5-4.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-8Figure 5-4Indicative Discharge Locations for Wetland / forest Effluent ManagementSystemsAn initial review of soil landscape and topographical mapping for the area revealed sufficient variationin site and soil characteristics to warrant development of site specific input data. In order to achievethis, a hypothetical wetland / forest location was assigned for each discharge location. A rapiddesktop assessment was completed to identify land likely to be suitable for the wetland forest systembased on:• proximity to the discharge location and/or developed areas;• soil landscape characteristics;• potential for frequent flooding or groundwater inundation; and• existing land use.It must be stressed that this assessment was undertaken purely to develop meaningful data inputs forthis modelling. Further, more detailed investigations (including field assessments) will be required toconfirm the suitability of any particular parcel of land. Importantly, the potential for Council to gainaccess to any of these sites has not been determined. A summary of the broad suitability of the fourdischarge locations for establishment of a wetland forest effluent management system is provided inTable 5-1.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-9Table 5-1Broad Site Suitability Analysis for Wetland Forest LocationsParameter Tuckombil Canal Brandy Arm Creek Doonbah Iron GatesAvailable Area Yes Yes No NoCurrentUseLandGrazing/scrub/wetland Sugarcane/grazing/scrub NationalPark/wetland/scrubLandscape Floodplain/backswamp Floodplain/lower Aeolian LowerAeolian/disturbedScrub/futureurbanLowerAeolian/beachridgeSoil Alluvial/estuarine clay Estuarine clay/sands Low lying sands Sands/loamsGroundwater 0–2 m 1–4 m 1 0–2 m 0-4 m(below surface)Green = High suitability. Orange = Moderate suitability. Red = Poor suitability.1. A greater separation distance between the point of effluent discharge and groundwater reduces risk of pollution.The two downstream locations (Doonbah and Iron Gates) are not considered viable locations for awetland forest effluent management system based on current land use and (to a lesser extent)landscape characteristics. The discharge locations have only been included to provide a comparisonof the variation in water quality impacts across a wide range of environments. It is highly unlikely thata wetland forest effluent management system could be established at these locations.5.3.2.1 Soil and Groundwater DynamicsProvided in this section is a general discussion of soil and groundwater characteristics within thestudy area and the implications for establishment of a wetland forest effluent management scheme.It is provided as a guide to the relative potential for impacts between predominantly clay or sandbased landscapes along the Evans River to prompt further discussion and direct future investigationsinto feasibility. It should be acknowledged, however, that the establishment of the wetland forestsystem was identified as marginal for the two low-lying sand landscape sites (Doonbah and IronGates) based on existing land use and available land.Previously suggested preference for a clay based, low lying landscape for establishment of thewetland forest is an oversimplification of soil and groundwater dynamics. In selecting the indicativelocations, BMT WBM considered a range of factors influencing performance of the system. Thisincluded land use, soil hydraulic and chemical properties, long-term and episodic groundwaterdepths, topography, anticipated groundwater dynamics and suitability for establishment of a mix ofwetland tree species. When considering low lying, flat sites, vertical saturated hydraulic conductivityis rarely the only factor governing deep drainage to the shallow, unconfined aquifer below. Thepresence of sandy soils does not automatically mean a higher potential for groundwater or surfacewater (via groundwater discharge) pollution. Irrespective of soil permeability, groundwater flowvelocity is primarily influenced by the very low hydraulic gradients typically present on a floodplainwhere relief is

WETLAND AND CARBON SEQUESTRATION MODELLING 5-10When assessing the potential for detrimental impacts on groundwater quality, it should be based onthe highest potential beneficial use. Groundwater flow in the aquifer in question (shallow unconfinedaquifer connected to the Evans River) is almost certainly to the south (to Evans River). No registeredbores exist between any of the indicative sites and the Evans River but some are located upstream,within sufficient proximity to warrant further consideration (e.g. risk of drawing effluent plumesupstream). These nearby bores are predominantly used for irrigation and stock water supply,however some are owned by Rous Water for the purpose of potable water supply. Progression of thewetland forest concept will require completion of a risk assessment in relation to these bores. Giventhat the predicted effluent quality from the polishing wetland is already predicted to be at or very nearto ANZECC low risk triggers for ecosystem protection and that MEDLI modelling predicts even lowerconcentrations for deep drainage to groundwater, the only potential beneficial groundwater use thatcould present a risk would be potable consumption (and even that is a very low risk).The volume of deep drainage predicted by WCG (2009) for the Dungarubba soil landscape was asubstantial underestimate derived through adoption of an unrealistically low saturated hydraulicconductivity value. This also resulted in a significant overestimate of runoff volumes. The low lyingflat nature of this landscape results in far higher deep drainage outputs to groundwater, even in claysoils. Groundwater recharge will obviously be lower on clay based soils than sands. However, asshown in Figure 5-11 (water balance), deep drainage is likely to be the predominant output relative torunoff for all the sites.BMT WBM does not consider the risk to groundwater to be significantly different for any of thesehypothetical sites (at this stage in the assessment process). Regardless of location, there is a needto refine and firm up details of any actual potential forest sites and undertake appropriate site and soil/ groundwater investigations prior to confirming feasibility. Current available information on soil andhydrogeology do not suggest the higher volumes of deep drainage expected on low lying sandlandscapes will manifest into higher risks. Regardless of physical conditions, the following factors allcompound to mitigate risks.• polishing wetland effluent quality (at or very near ANZECC low risk trigger values); and• pollutant attenuation processes in the forest and shallow groundwater.5.3.3 Free Surface Water Wetland Treatment PerformanceIt was considered most appropriate to calculate a single average effluent quality concentration foreach parameter given that the Reed model is a steady state process model and there is a limitedamount of applicable performance data and a full concept design is yet to be developed. Dailyvariability in effluent quality may be incorporated into the assessment in the future (possibly usingscaled West Byron STP data to mimic natural variation) should the concept be pursued further.5.3.3.1 Inflows from Evans Head STPAverage daily effluent flow delivered to the treatment wetland (2,025 kL/day) was calculated from theBase Flow scenario (continuous discharge) provided to BMT WBM by Hydrosphere Consulting anddetailed in their report (Hydrosphere, 2010). Statistical analysis of effluent quality data for EvansHead STP (supplied by Council) was used to derive input concentrations for the wetland model. Onlypost-treatment system upgrade effluent quality data (post September 2007) were used to representfuture performance. STP inflow data used in wetland modelling are summarised in Table 5-2.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-11Table 5-2Average Inflow Characteristics from Evans Head STP to WetlandParameter Unit AverageFlow kL/day 2,025Biochemical Oxygen Demand 1.75Total Suspended Solids 8.04Total Nitrogen 5.34Oxidized Nitrogen mg/L 3.68Ammonium 0.5Organic Nitrogen 1.16Total Phosphorus0.317Faecal Coliform cfu/100ml 635.3.3.2 Wetland ConfigurationInput parameters were derived following review of Section 4.1 and 6.2 of the WCG FeasibilityAssessment. Operational depth of the wetland was assigned based on HRT and surface area. Atthis preliminary assessment stage, there is little benefit altering the assumed configuration. Wetlandconfiguration data used in the modelling is summarised in Table 5-3.Table 5-3Assumed Wetland Configuration for ModellingParameter Unit ValueLength 300Width m 500Operational Depth0.25Effective Porosity decimal 0.65No. cells in series No. 1Minimum water temperature deg. C 145.3.3.3 Rate Constants and Temperature CoefficientsWhere appropriate data is available, it is advisable to develop or obtain local / comparable rateconstants for use in wetland process modelling. Detailed design of such a wetland typically involvespilot testing at the selected site using the actual effluent to be treated. Where such data are notavailable, the default constants provided by Reed et al (1995) are conservative and will thereforeunderestimate performance. Performance data from similar polishing wetlands servicing the WestByron STP were provided by Byron Shire Council (Australian Wetlands, 2006) as a potential sourcefor more applicable rate constants.Basic information on the configuration and effluent inputs were used in conjunction with pollutantremoval performance data to populate and calibrate a Reed model for the West Byron STP wetlands.Calibration involved iterative adjustment of rate constants until effluent quality matched performancedata from Australian Wetlands (2006). These constants should be considered approximations onlyas they are based on limited information regarding wetland configuration and a relatively shortmonitoring period. The West Byron Rate constants are compared to the default Reed et al (1995)values in Table 5-4.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-12Table 5-4 Comparison of Potential Rate ConstantsParameterRate Constant (days – d -1 )Reed et al (1995) West Byron STPBOD 5 0.678 0.03NH 4 0.2187 0.8NO 3 1 4Faecal coliform 2.6 27It can be seen that the treatment performance of the West Byron STP wetland is significantly betterthan typical performance of wetlands used to develop the Reed model. However some caution isadvisable in adopting these numbers prior to developing a concept and process design, particularly inlight of the higher nitrogen concentration and lower HRT at West Byron. Models were built using bothrate constants for consideration in MEDLI modelling of the carbon forest. Given the predicted effluentconcentrations result in very small nutrient loads being applied to the forest (i.e. forest growth rate ispredicted to be nutrient limited), the more conservative Reed constants were adopted for thepreliminary assessment.5.3.3.4 Background ConcentrationsThe Reed model requires the nomination of a C* background concentration to be used to limitpollutant removal based on observed performance of wetlands. Natural nutrient cycling andheterogeneous flow conditions within a wetland invariably limit the ability of the system to reduceconcentrations below a baseline level. Background concentrations were adopted from measuredaverage outlet concentrations at West Byron STP wetland unless the value was too small for use inMEDLI. Nutrient concentrations can only be entered into MEDLI to a single decimal place largelybecause a daily mass balance model is not accurate beyond this level and any reductions below thisvalue are likely to be artificial.Table 5-5Adopted Background Concentrations (C*) for Wetland TreatmentParameter Unit C* SourceBiochemical Oxygen Demand 2Total Suspended Solids 3 West Byron STP 1Total Nitrogen 1.0Oxidized Nitrogen mg/L 0.1Ammonium 0.1MEDLIOrganic Nitrogen 0.8 West Byron STP 1Total Phosphorus0.1 MEDLIFaecal Coliform cfu/100ml 2000 Reed et alNote 1 – Australian Wetlands (2006)5.3.4 Hydrology and Nutrient ProcessesA set of MEDLI models were constructed to model the four different indicative wetland locations, dailytime series of inflows and variations in soil / landscape characteristics. A total of 20 MEDLI modelswere required to capture all variation in these parameters.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-135.3.4.1 STP Inflow and ConcentrationIn order to model both the wetland and forest water balance accurately, the daily time series of inflowcoming from the Evans Head STP (supplied by Hydrosphere, 2010) was imported into MEDLI usingthe ‘Other’ waste estimation function and editing the input file manually in a text editor. This wasconsidered necessary following a comparison of the inflows adopted during WCG MEDLI modelling(using the ‘Municipal STP, Average’ waste estimation function) compared to the daily flow valuesadopted (2050) for this preliminary assessment as shown in Figure 5-5.Figure 5-5Comparison of WCG MEDLI STP Inputs and Values Adopted for this StudyAverage wetland effluent nutrient concentrations derived using the Reed model were inserted intoMEDLI. As previously stated, nutrient concentrations less than 0.1 mg/L cannot be modelled withinMEDLI. As explained in Section 5.3.6 this has not influenced the results of this preliminaryassessment.5.3.4.2 ClimateMEDLI requires daily rainfall, evaporation, solar radiation, maximum and minimum temperature forthe irrigation site. For this study interpolated data from SILO (DataDrill) was obtained in MEDLIformat from Queensland DERM for a central location between Evans Head and Woodburn along theEvans River (29.1 deg. S, 153.4 deg. E) as shown in Table 5-6. Data was checked against Bureau ofMeteorology (BOM) station data used for other aspects of this assessment and found to beconsistent. The MEDLI modelling period was set at 53 years (1957 – 2009) to avoid use of SILOevaporation data pre-1956 which are average monthly values due to a lack of data for interpolation.The 53 year period is considered adequate to ensure the forest matures to a relatively steady rate ofgrowth and associated water and nutrient uptake by 2007-2009.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-14Table 5-6Summary Statistics for SILO MEDLI Climate Data5.3.4.3 System dimensions and configurationThe ‘Pond’ module of MEDLI was used to calculate the water balance for the treatment wetland byassigning input values that reflected the hydraulic characteristics of the wetland as a pond (i.e.bucket). Key considerations in developing pond parameters included:• maintaining a surface area to ensure equivalent evaporation values;• allowing for a 0.25m minimum operational depth for the wetland by adjusting the modelled depth;and• adjusting depths based on the 0.65 void space factor taken from Reed et al (1995).Key adopted parameters are shown in Figure 5-6.Figure 5-6MEDLI Pond Input ParametersG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-15In addition to these input values, a seepage rate of 0.1 mm/day and pan evaporation factor of 0.7were also adopted.A total irrigated wetland forest of 125 ha was retained from WCG (2009) for this preliminaryassessment. Should this effluent management option be pursued, the models can be used tooptimise the size of both the treatment wetland and forest.5.3.4.4 Soil and Landscape CharacteristicsAdoption of inappropriate or generic soil and landscape parameters in MEDLI can result in order ofmagnitude variations in results as was the case with the WCG (2009) assessment. To ensureadopted values were representative and based on best available information a desktop site and soilassessment was undertaken using the following resources:• Soil Landscapes of the Woodburn 1:100,000 Sheet (Morand, 2001);• Soil and Land Information System (SALIS) database;• Aerial photography;• Digital Elevation Model (DEM);• Land use; and• Cadastre and other spatial datasets.Four indicative wetland / forest sites were nominated as described in Section 5.3.2 and shown inFigure 5-4. MEDLI soil parameters were developed based on SALIS profile data (mostly obtainedduring field investigations for soil landscape mapping) considered applicable to site and soilconditions at each discharge point and irrigation site. Two of the five soil profiles were obtained fromthe local soil landscape facet, but occurred geographically outside of the study area. In these casesthe external profile best represented local variation observed within the soil facet. This variationrelated to landscape position (e.g. floodplain, backswamp, alluvial terrace, Aeolian ridge) andgroundwater elevation. Distinction between soil types was only made where it was potentially goingto alter the outcomes of the modelling.Five soil types were parameterised for MEDLI based on this assessment using the soil landscapefacet from Morand (2001) and discharge site as identifiers. Only one discharge site was found tohave multiple soil types present that warranted different MEDLI parameters (Brandy Arm Creek).Figure 5-7 shows the soil landscape facets located within the study area in addition to three of fiveSALIS profiles used in the assessment. The remaining two profiles were located outside the studyarea but were utilised based on the similarity between landscapes.MEDLI soil parameters for the five soil types used in modelling are summarised in Table 5-7 andTable 5-8. Some parameters were inferred based on field texture, structure, colour and depth usingpublished data on Australian soils (Gardner and Davis, 1998, Hazelton and Murphy, 2007).G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-17Table 5-7MEDLI Soil ParametersG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-18Table 5-8MEDLI Soil Parameters (Continued)5.3.4.5 Plant (Forest) ParametersWhen tree species are to be modelled in MEDLI it is typical for the ‘Monthly Covers’ option to beselected from the Plant module. This allows soil evaporation and transpiration to be calculated butnot biomass accumulation (tree growth) or nutrient uptake and dynamics. For this assessment, it waspreferable to include a dynamic plant growth module that acknowledged the slowdown in growth andtranspiration associated with maturing of a tree stand and allowed calculation of nutrient uptake anddynamics.To achieve this, the Pasture module was used and Melaleuca alternifolia selected as the plantspecies. This particular species of large shrub / small tree most closely represents the type ofvegetation present in the wetland forest. Input parameters were modified to achieve the following:• A gradual reduction in biomass accumulation as the forest matures by adopting a very largeharvest trigger; and• Evapo-transpiration rates that are comparable to measured values for trees on the NSW northcoast (Myers et al, 1999).G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-19Adopted parameters are shown in Figure 5-8. Biomass accumulation (standing yield) andaccumulated nutrient uptake is shown in Figure 5-9.Figure 5-8MEDLI Plant ParametersWetland Forest Growth Rate89.72.731.074.72.225.859.81.820.744.81.315.529.90.910.314.90.45.20.00.00.01957 1965 1973 1981 1989 1997 2005 2013Evans_River_Pasture\Crop, Nitrogen Uptake - accum. (kg/ha since harvestx100Daily ( 1/ 1/1957 - 31/12/2008), DEvans_River_Pasture\Crop, Phosphorus Uptake - accum. (kg/ha since harvest), Daily ( 1/ 1/1957 - 31/12/2008)Evans_River_Pasture\Crop, Dry Matter Standing Yield (kg/hax10000), Daily ( 1/ 1/1957 - 31/12/2008)Figure 5-9Biomass Accumulation (Standing Yield) for the Wetland ForestLong Term MaintenanceWater and nutrient uptake of the forest has been based on a mature stand of vegetation (i.e. noharvesting in 53 years) and therefore represents performance under a very low maintenance regime.Some level of harvesting may be desired to maintain carbon capture / neutral operation and this willneed to be evaluated as part of concept development. Harvesting of trees will initially reduce nutrientG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-20uptake, followed by a period of higher uptake during early growth stages. Assuming the forest is leftunharvested, typical maintenance activities will include normal pest/weed control and upkeep of thepump and irrigation infrastructure. There will also be a need to maintain adequate distribution ofirrigation water over the forest site. Detailed maintenance requirements can be developed once asuitable site and concept design is developed.5.3.4.6 Irrigation Infrastructure and SchedulingFor this preliminary assessment model, a simple set of assumptions were used to simulate irrigationof the wetland forest. Because the wetland forest will be operating as a partial reuse and partialdisposal system it is likely that a fixed rate irrigation schedule would be adopted. Irrigation is onlylikely to cease during extreme events where the site is subject to flood inundation. For the purpose ofthis modelling it has been assumed that the wetland forest is bunded and a single, controlled surfacedischarge point to the Evans River constructed. In addition to controlling surface discharge, thiswould also allow forest hydrology to mimic that of a wetland environment.Flood irrigation has been assumed for the method of irrigation given the bunded, wetlandconfiguration. A minimum irrigation depth of 0.5 mm/day has been set to represent a nominal depthrequired to warrant operation of infrastructure. A fixed rate schedule has the advantage of being avery simple system requiring limited control or operational supervision. A disadvantage is the lessthan optimum rate at which water is supplied to the forest does result in minor water stress duringwarmer months. MEDLI irrigation parameters are shown in Figure 5-10.Figure 5-10 MEDLI Irrigation ParametersG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-215.3.4.7 MEDLI Model RunsIn order to capture all of the potential variation in site conditions and STP inflows, 20 iterations of the4 MEDLI models were run. Results for the entire 53 year period were extracted for use in preparingthe daily time series for receiving water modelling. These model runs are summarised in Table 5-9.Table 5-9MEDLI Models and Iterations5.3.5 PathogensMEDLI currently does not model pathogen dynamics in an effluent irrigation system (other thanthrough aerosol spray drift). In order to include pathogens in this assessment, the DSM was used tomodel soil viral dieoff, leaching and surcharge in runoff. Faecal coliform were selected as thepathogenic indicator for modelling due to availability of data. The algorithms of the DSM relate toviruses rather than bacteria, however this makes the modelling conservative given that virus survivalin the environment is typically longer than bacterial survival times (USEPA, 2002).DSM modelling used daily soil water balance outputs from MEDLI (profile soil water, irrigated effluent,runoff and deep drainage) along with ground temperature and effluent faecal coliform concentrationto calculate the number of organisms present in the soil profile at the end of each day. PotentialG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-22outputs are viral dieoff and adsorption, leaching and runoff. DSM inputs are summarised in Table5-10.Table 5-10DSM Virus Input DataInput Unit SourceIrrigation Area m 2 WCG (2009)Effluent Faecal Coliform cfu/100 mL Reed Wetland ModelSoil Saturated Water ContentSoil Profile WaterRunoffmmDeep DrainageMEDLIIrrigationAverage Temperatureº C5.3.6 Time Series for ModellingDaily time series from MEDLI and DSM modelling were then analysed to gain an understanding ofwater, nutrient and pathogen dynamics for each of the four indicative wetland forest sites. Effluentcontributions to nutrient loads were clearly identified as a minor component of the total typical nutrientcycle of a wetland forest with MEDLI determining that all sites would be nitrogen deficientpermanently. However, it was considered inappropriate to adopt the surface nutrient outputs fromMEDLI to represent runoff concentrations because MEDLI does not include nutrient additions fromdecaying vegetation (the major source of nutrients in a wetland forest) in its calculations.Consequently, MEDLI results can be considered representative of site hydrology and subsurface(deep drainage) nutrient loads, but not surface nutrient loads. The DSM more accurately modelssurface surcharge of pathogenic indicators and has been used to develop runoff faecal coliformloads.To address this issue, it is appropriate to assume that (as a result of the very low effluent nutrientconcentrations applied to the forest) the primary impact on surface nutrient export of such a schemearises from a change in hydrology. The importation (irrigation) of water from outside of this subcatchmentincreases soil water, deep drainage and surface runoff events in comparison to a nonirrigatedsite. For the four indicative sites in question, the biggest change was made to deepdrainage.To ensure consistency between catchment and wetland forest modelling, the Event MeanConcentrations (EMC) adopted for catchment modelling (see Appendix D) for a forest land use wereapplied to surface runoff volumes from the wetland forest. At this preliminary stage insufficientinformation is available to develop more site specific values.Deep drainage hydraulic, nutrient and pathogen contributions to the Evans River were not included inthis preliminary assessment for the following reasons.• In the case of phosphorus and faecal coliform loads, MEDLI predicted very low average annualconcentrations in deep drainage that would be rapidly attenuated in shallow groundwater flow;• There is currently insufficient information on or understanding of groundwater flow and qualitydynamics along the Evans River floodplain to make confident assumptions regarding surfacewater – groundwater connectivity and pollutant attenuation;G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-23• Based on groundwater assessments for effluent irrigation schemes in coastal areas previouslyundertaken by BMT WBM, it is likely that the low groundwater velocities provide sufficient bufferto ensure increased groundwater discharge quality to the Evans River created by a wetlandforest scheme returns to background concentrations on an average annual basis;Based on the above, it is reasonable to assume that any pollutant contributions to the Evans River viashallow groundwater flow would be accounted for in baseflow (Dry Weather Concentrations) loadscalculated through catchment modelling.Overflow volumes from the treatment wetland were included in the combined time series for riverdischarge with effluent quality from the Reed model adopted. The 2007-2009 period did not includeany wet weather overflows from this wetland.The potential discharge site upstream of Brandy Arm Creek incorporated two distinctly different soiltypes and as a result two MEDLI / DSM models were established. Results were combined based onthe proportional area of the total wetland forest site occupied by each soil landscape facet.A separate MEDLI iteration was run using STP inflow time series for 2008/2007, 2008 and 2009respectively. The 53 year period allowed the various modules of MEDLI and the DSM to warm up torepresent a mature wetland forest irrigation scheme before 2007 (particularly, soil water status,phosphorus sorption, nitrogen in soil storage / solution and faecal coliform concentrations in soilsolution). To create the final time series, results were extracted from each of the three iterations andcombined as summarised in Table 5-11.Table 5-11Source of Time Series Results for Wetland Forest ModellingMEDLI/DSM IterationPeriod used in Time SeriesResults2008/2007 16/10/2007 – 31/12/20072008 1/1/2008 – 31/12/20082009 1/1/2009 – 31/12/20095.4 ResultsDaily time series results for surface hydraulic, nutrient (including species) and pathogenic indicatorloads were prepared in spreadsheet form for use in the preliminary assessment. Figure 5-11 toFigure 5-13 summarise the average annual results for the Tuckombil Canal and Brandy Arm Creeksite over the 16/10/2007 to 31/12/2009 period. Further summary data is provided in Table 5-12.Faecal coliform concentrations (average annual) were

WETLAND AND CARBON SEQUESTRATION MODELLING 5-24significantly increase evapo-transpiration rates for both sites (Tuckombil Canal greater than BrandyArm), it will slightly increase deep drainage (Brandy Arm greater than Tuckombil Canal) and it willlead to slight decreases in surface runoff (similar magnitude of reduction at both sites).The changes in predicted evapo-transpiration rates vary between sites largely due to differences insoil water storage capacity. Higher soil storage capacity provides greater opportunities for effluent tobe available for plant uptake and evaporation. Similarly, runoff volumes vary as a result ofdifferences in soil storage capacity and hydraulic conductivity which affects the quantity of waterwhich runs off to the estuary or which goes into groundwater stores.2500Evapo-transpiration Deep Drainage Runoff20001500mm/year10005000Tuckombil Canal ExistingTuckombil Canal withSTP Wetland / ForestBrandy Arm CreekExistingBrandy Arm Creek withSTP Wetland / ForestFigure 5-11 Water Balance for Selected Wetland / Forest SitesG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-251000Evapo-transpiration Deep Drainage Runoff800600mm/year4002000-200Tuckombil CanalBrandy Arm CreekFigure 5-12 Net Changes in Water Balance for Selected Wetland / Forest SitesFigure 5-13 identifies that due to the predicted reductions in surface runoff (as shown in Figure 5-10)from the wetland/forest sites, there is a corresponding net reduction in total nutrient loads dischargedto the Evans River estuary.300TNTP200100kg/year0-100-200-300Tuckombil CanalBrandy Arm CreekFigure 5-13 Net Changes in Total Nutrients Loads for Selected Wetland / Forest SitesG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WETLAND AND CARBON SEQUESTRATION MODELLING 5-26Table 5-12Net changes in Water Balance and Pollutant Load Discharges from SelectedWetland / Forest SitesEvapotranspirationDeepDrainageSurfaceRunoffLocationTN Load TP Loadmm/year mm/year mm/year kg/year kg/yearTuckombil Canal 645 31 -50 -244 -7Brandy Arm Creek 552 120 -51 -211 -65.5 Outcomes and RecommendationsThe broad site suitability assessment discussed in Section 5.3.2 effectively eliminated Doonbah andIron Gates as potential locations for a wetland forest effluent management system based onfeasibility and as a result these sites have not been considered further.Modelling results for the other sites suggest that the implementation of the STP wetland / forestscheme will affect the net water balance of the site. Modelling indicates that the scheme willsignificantly increase evapo-transpiration rates for both sites (Tuckombil Canal greater than BrandyArm), slightly increase deep drainage (Brandy Arm greater than Tuckombil Canal) and will lead toslight reductions in surface runoff (similar magnitude of reduction at both sites).The changes in predicted evapo-transpiration rates vary between sites largely due to differences insoil water storage capacity. Higher soil storage capacity provides greater opportunities for effluent tobe available for plant uptake and evaporation. Similarly, runoff volumes vary as a result ofdifferences in soil storage capacity and hydraulic conductivity which affects the quantity of waterwhich runs off to the estuary or which goes into groundwater stores. However, it is important to notethat connectivity between shallow groundwater and the Evans River is yet to be investigated in anydetail. Similarly, the impact on long-term groundwater elevation of irrigation on the sandy sites hasnot been estimated.Overall, the outcomes of this preliminary assessment indicate that a high level of water qualityprotection is likely to result from implementation of a wetland / forest effluent management scheme.This preliminary assessment was suitably conservative and it is envisaged that actual performancewould be better than predicted. It must be recognised that this is a desktop modelling exercise andadditional model parameterisation and/or calibration is recommended if the option is to be consideredfurther. As an example, the location of any preferred sites may influence the magnitude of riverdischarge loads.It is recommended that site specific data (at the very least for each landscape type observed alongthe Evans River) be obtained on landscape and soil characteristics through field investigations for thenext phase of investigations. Similarly, further investigation of interactions between such a scheme,groundwater and the Evans River estuary is also recommended. Refinement of the concept designmay also provide some improvements to performance and system footprint (and cost) and this couldbe done using the modelling methodology adopted for this assessment. This should includerefinement of treatment wetland process design and forest growth characteristics for modelling.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-16 HYDRODYNAMIC MODELLING6.1 ApproachThe methodology for evaluation of hydrodynamic (HD) and advection-dispersion (AD) processes wasbased on coupled two-dimensional (depth-averaged) modelling. The package that was used to thisend was RMA10S, which is a finite element model that handles both HD and AD components.One advantage of employing the finite element model framework is its ability to adjust the spatialresolution of the computational network, and in particular, to increase resolution in areas of specificinterest to the study.6.2 Selection of Modelling PeriodsBased on the availability of data as described in Section 2, the following periods were selected forsubsequent modelling purposes:• Hydrodynamic Model Calibration: 31/01/2010 to 19/02/2010 – This model calibration was basedon the field measurements collected by BMT WBM for this study (refer to Section 2.1);• Hydrodynamic Model Validation: 01/11/2005 to 31/05/2006 – This model validation was basedon the Evans River monitoring undertaken by MHL in 2005/2006 and focused on tidal levelsalong the reaches of the river (refer to Section 2.3);• Advection-Dispersion Model Calibration: 21/07/2006 to 31/12/2006 – This model calibration wasbased on the available Council collected electrical conductivity data within the Evans River andfocused primarily on the reproduction of the salinity recovery rates after specific rainfall events.Given the small estuary size and relatively rapid recovery (as seen in the monitoring data)replicating this behaviour was deemed sufficient for the purposes of calibrating the modeldeveloped in this study; and• Scenario Modelling: The scenario modelling period was selected as 1/1/2008 to 31/12/2008.This encompassed a period of best available data and was suitable for calculation of annualmedian concentrations, consistent with comparison with chronic (i.e. long term) water qualityobjectives.6.3 Model Development6.3.1 Model Extent and Mesh DefinitionThe hydrodynamic model mesh developed for this study extends from the Tuckombil weir and canal,downstream out to the sea past the Evans River entrance. Major tributaries and/or mangrove areasalong the estuary have also been included in the mesh, in order to accurately represent the tidalstorage within the river system and simulate the tidal flux.Particular attention was also given to the extent of the mesh into the ocean, with the mesh covering asufficient area offshore in order to capture the circulatory patterns within the coastal embayment, andas such potential interaction of river discharges onto the adjoining beaches.The developed model mesh for the study area is shown in Figure 6-1.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-36.3.2 BathymetryA Digital Elevation Model (DEM) of the study area was derived from various survey components, asdescribed in Section 2.5.In developing the hydrodynamic model, consideration was given to the underlying bathymetry indefining the mesh configuration. For example, model resolution was enhanced at locations of rapidlyvarying bathymetry or expected high velocity/flow regions based on the main channel definition.A point inspection of the DEM was used to define the bed elevation at the model computation points(nodes) located at the vertices of each individual elements of the mesh. It is noted that some smalladjustments to bathymetry in localised areas (specifically along the ocean open boundary) wasnecessary to promote model stability.Figure 6-2 presents the bathymetry data associated with the model mesh.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-56.3.3 Tidal Boundary ConditionsThe developed model extent included a single arc open boundary (see Figure 6-1) that requiredtemporal definition of water surface elevations. Tidal data along this boundary was uniformly definedfrom the various tidal datasets, depending on the modelling period, as follows:• BMT WBM CTD measurements at the Evans River entrance for the HD calibration period;• MHL temporary tide records at the Evans River entrance for the HD validation period; and• Ballina tide records for the AD calibration period and subsequent scenario modelling.These tidal elevations, water surface elevations (WSE) are reported in Figure 6-3 to Figure 6-5,respectively. Only the first four months of the AD calibration tidal boundary are presented here forclarity.1.210.80.60.4WSE (m AHD)0.20-0.2-0.4-0.6-0.8-131/01/20100:002/02/20100:004/02/20100:006/02/20100:008/02/20100:0010/02/20100:0012/02/20100:0014/02/20100:0016/02/20100:0018/02/20100:0020/02/20100:00Figure 6-3HD Calibration Tidal Boundary1.210.80.60.4WSE (m AHD)0.20-0.2-0.4-0.6-0.8-119/11/2005 0:00 9/12/2005 0:00 29/12/2005 0:00 18/01/2006 0:00 7/02/2006 0:00 27/02/2006 0:00Figure 6-4HD Validation Tidal BoundaryG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-61.210.80.60.4WSE (m AHD)0.20-0.2-0.4-0.6-0.8-121/07/2006 0:00 10/08/2006 0:00 30/08/2006 0:00 19/09/2006 0:00 9/10/2006 0:00 29/10/2006 0:00 18/11/2006 0:00Figure 6-5AD Calibration Tidal Boundary6.3.4 Meteorological Wind ForcingWind data (speed and direction) was sourced from the Bureau of Meteorology at the Evans HeadRAAF Bombing Range Station (#058212). Refer to Section 2.4 for further details.The wind field was applied uniformly across the entire model area.6.3.5 Material PropertiesWithin the RMA model, various hydraulic properties (e.g. hydraulic roughness) can be assigned togroupings of model elements. This involves the specification of a spatial distribution of variousmaterial types with common properties. For example, all model elements representing mangroveareas can be given a specific material type classification, from which it is possible to prescribe acommon Manning’s n roughness coefficient. A representation of this material classification adoptedfor the model is shown in Figure 6-6.This distribution was based both on the Evans River ecosystem characteristics (including mangrove,seagrass and saltmarsh areas as per NSW DNR vegetation map) and the bathymetry of the model.A total of nine (9) main areas were defined as shown in Table 6-1.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-8Table 6-1Evans River RMA Model Material Categories and Associated RoughnessMaterial CategoryHigh Land(elevation > 0m AHD)Shallow Areas(elevation > -1m AHD)Main Channel - Mud(elevation > -5m AHD)Main Channel - Sand(elevation > -5m AHD)Main Channel - Slippery(elevation > -5m AHD)Open Ocean(elevation < -5m AHD)Roughness Value(Manning’s n)0.0280.0280.0250.0200.0180.025Saltmarsh 0.040Mangrove 0.045Seagrass 0.050The roughness values associated with each of these categories were refined during the HDcalibration process. Refer to Section 6.4.1 for further details.6.3.6 Advection Dispersion ParameterisationTo accurately capture advection and dispersion, the model required input of dispersion coefficients.These coefficients determine the resultant spread of particles throughout the model domain. Thesame element type distribution presented above was used to describe the AD parameterisation, andis discussed in further detail below in Section 6.4.4.6.4 Model Calibration and Validation6.4.1 Hydrodynamic Calibration6.4.1.1 Calibration DataThe hydrodynamic model was calibrated against the CTD and ADCP data collected by BMT WBM inearly 2010 as part of this study. This included the following datasets:• Tidal levels at three locations along the estuary; and• Tidal flows (both neap and spring tides) at a section near the river entrance; and• Tidal flows (only spring tide) at a section upstream of the estuary.This field collection and the resulting datasets are presented in detail in Section 2.1.6.4.1.2 Calibration Results – Water LevelsWater surface elevation results from the RMA model were extracted over the HD calibration periodand are presented below in Figure 6-7 to Figure 6-13 against the recorded datasets.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-9These figures present both the entire calibration period (i.e. 31/1/2010 to 19/2/2010), as well asselected shorter periods at each location, in order to provide a better zoom on the tidal cycles.Discussion of the RMA results and the model performance is provided at the end of this section.1Upstream 1RecordedModelled0.80.60.4WSE (m AHD)0.20-0.2-0.4-0.6-0.8-11/02/20100:003/02/20100:005/02/20100:007/02/20100:009/02/20100:0011/02/20100:0013/02/20100:0015/02/20100:0017/02/20100:00Figure 6-7 HD Calibration – Water Levels – Upstream 11Upstream 1RecordedModelled0.80.60.4WSE (m AHD)0.20-0.2-0.4-0.6-0.8-12/02/20100:002/02/20104:482/02/20109:362/02/201014:242/02/201019:123/02/20100:003/02/20104:483/02/20109:363/02/201014:243/02/201019:124/02/20100:00Figure 6-8HD Calibration – Water Levels – Upstream 1 – ZoomG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-10Upstream 2RecordedModelled10.80.60.4WSE (m AHD)0.20-0.2-0.4-0.6-0.8-11/02/20100:003/02/20100:005/02/20100:007/02/20100:009/02/20100:0011/02/20100:0013/02/20100:0015/02/20100:0017/02/20100:00Figure 6-9 HD Calibration – Water Levels – Upstream 2Upstream 2RecordedModelled10.80.60.4WSE (m AHD)0.20-0.2-0.4-0.6-0.8-18/02/20100:008/02/20104:488/02/20109:368/02/201014:248/02/201019:129/02/20100:009/02/20104:489/02/20109:369/02/201014:249/02/201019:1210/02/20100:00Figure 6-10 HD Calibration – Water Levels – Upstream 2 – ZoomG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-11DownstreamRecordedModelled10.80.60.4WSE (m AHD)0.20-0.2-0.4-0.6-0.8-11/02/20100:003/02/20100:005/02/20100:007/02/20100:009/02/20100:0011/02/20100:0013/02/20100:0015/02/20100:0017/02/20100:00Figure 6-11 HD Calibration – Water Levels – DownstreamDownstreamRecordedModelled10.80.60.4WSE (m AHD)0.20-0.2-0.4-0.6-0.8-12/02/20100:002/02/20104:482/02/20109:362/02/201014:242/02/201019:123/02/20100:003/02/20104:483/02/20109:363/02/201014:243/02/201019:124/02/20100:00Figure 6-12 HD Calibration – Water Levels – Downstream – Zoom 1G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-12DownstreamRecordedModelled10.80.60.4WSE (m AHD)0.20-0.2-0.4-0.6-0.8-18/02/20100:008/02/20104:488/02/20109:368/02/201014:248/02/201019:129/02/20100:009/02/20104:489/02/20109:369/02/201014:249/02/201019:1210/02/20100:006.4.1.3 Calibration Results – FlowsFigure 6-13 HD Calibration – Water Levels – Downstream – Zoom 2Flow results from the RMA model were extracted at two sections where ADCP transects wererecorded (see Figure 2-1) are presented below in Figure 6-14 to Figure 6-16 against the recordeddatasets.Upstream Spring TideRecordedModelled200150100Flow (m3/s)500-50-100-150-2003/02/2010 12:00 3/02/2010 14:24 3/02/2010 16:48 3/02/2010 19:12 3/02/2010 21:36 4/02/2010 0:00 4/02/2010 2:24Figure 6-14 HD Calibration – Spring Tide Flows – Upstream SectionG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-13200Downstream Spring TideRecordedModelled150100Flow (m3/s)500-50-100-150-2002/02/2010 9:00 2/02/2010 11:24 2/02/2010 13:48 2/02/2010 16:12 2/02/2010 18:36 2/02/2010 21:00 2/02/2010 23:24 3/02/2010 1:48Figure 6-15 HD Calibration – Spring Tide Flows – Downstream SectionDownstream Neap TideRecordedModelled200150100Flow (m3/s)500-50-100-150-2008/02/2010 9:00 8/02/2010 11:24 8/02/2010 13:48 8/02/2010 16:12 8/02/2010 18:36 8/02/2010 21:00 8/02/2010 23:246.4.1.4 DiscussionFigure 6-16 HD Calibration – Neap Tide Flows – Downstream SectionThe following key points are noted in relation to the HD calibration of the model:• The graphs above in particular show the ability of the model to propagate the tidal boundary fromthe ocean into the mouth of the river, with tidal levels being replicated both in phase andamplitude at the downstream location (i.e. just upstream of the entrance – see Figure 2-1 forexact location);• The propagation of the tide upstream in the estuary, past the sand bar in the Iron Gates vicinity,is also replicated by the model, as seen in Figure 6-7 to Figure 6-10. The model seems tointroduce a small lag in the upper sections of the estuary, with a half-an-hour delay in the modelcompared to the records. It is however noted that this is the same as the resolution of the modeland is thus not considered significant;G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-14• Similarly, the amplitude is replicated by the model in the upper sections of the estuary, within a±5cm tolerance;• In terms of flows, the spring tide at the upstream section, and the neap tide at the downstreamsection are reproduced accurately by the model. The small amplitude of these flows is howevernoted here, with a maximum of about 50 m 3 /s in the downstream section for a neap tide and onlyabout 30 m 3 /s in the upstream section for a spring tide;• Flows observed during a spring tide at the downstream section are also reproduced by themodel, with predicted peak flows just short of the recorded flows by approximately 20%. Theactual timing of the tidal cycle is again reproduced well; and• Given the uncertainties associated with the model development, and in particular the inflowsprovided by the catchment model, it is believed that the results of this HD calibration meet therequirements of the current study and will allow for a representation of tidal flows suitable for theassessments of the STP release within the framework of this study.6.4.2 Hydrodynamic Validation6.4.2.1 Validation DataThe MHL tidal data collected in 2005-2006 in the Evans River Estuary was used to validate thehydrodynamic model. Refer to Section 2.3.1 for presentation of this data.The model calibrated as per above was thus executed over the period 19/11/2005 to 02/03/2006.Results were extracted at the various MHL recorded sites (including temporary and permanentrecorders – see Figure 2-12) and compared against the recorded water levels over this period.6.4.2.2 Validation Results – Water LevelsThis section presents the RMA model validation results over two specific periods: January 2005 andFebruary 2006. This second period is interesting as it includes a large rainfall/storm event whichgenerated weir overflow at Tuckombil. This catchment influence is observed in the tidal recordsthroughout the estuary, with in particular the attenuation of the tidal signal in the upper section of theestuary (Site 11 to Site 7) for a 3-day period from the 19 th of February 2006. Discussion of the RMAmodel results are provided in the following section.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-151.210.80.6Site 11 (Tucombil Canal Upstream) - MHL Temporary RecorderRecordedModelledWSE (m AHD)0.40.20-0.2-0.4-0.6-0.8-11/12/2005 0:00 6/12/2005 0:00 11/12/2005 0:00 16/12/2005 0:00 21/12/2005 0:00 26/12/2005 0:00 31/12/2005 0:00Figure 6-17 HD Validation – Water Levels – Site 11 – December 20051.210.80.6Site 9 (Brandy Arm Entrance) - MHL Temporary RecorderRecordedModelledWSE (m AHD)0.40.20-0.2-0.4-0.6-0.8-11/12/2005 0:00 6/12/2005 0:00 11/12/2005 0:00 16/12/2005 0:00 21/12/2005 0:00 26/12/2005 0:00 31/12/2005 0:00Figure 6-18 HD Validation – Water Levels – Site 9 – December 2005G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-16Site 7 (Evans River) - MHL Temporary RecorderRecordedModelled1.210.80.6WSE (m AHD)0.40.20-0.2-0.4-0.6-0.8-11/12/2005 0:00 6/12/2005 0:00 11/12/2005 0:00 16/12/2005 0:00 21/12/2005 0:00 26/12/2005 0:00 31/12/2005 0:00Figure 6-19 HD Validation – Water Levels – Site 7 – December 20051.2Iron Gate - MHL Permanent RecorderRecordedModelled10.80.6WSE (m AHD)0.40.20-0.2-0.4-0.6-0.8-11/12/2005 0:00 6/12/2005 0:00 11/12/2005 0:00 16/12/2005 0:00 21/12/2005 0:00 26/12/2005 0:00 31/12/2005 0:00Figure 6-20 HD Validation – Water Levels – Iron Gate – December 2005G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-171.210.80.6Site 5 (Iron Gates Downstream) - MHL Temporary RecorderRecordedModelledWSE (m AHD)0.40.20-0.2-0.4-0.6-0.8-11/12/2005 0:00 6/12/2005 0:00 11/12/2005 0:00 16/12/2005 0:00 21/12/2005 0:00 26/12/2005 0:00 31/12/2005 0:00Figure 6-21 HD Validation – Water Levels – Site 5 – December 20051.210.80.6Fishing Coop - MHL Permanent RecorderRecordedModelledWSE (m AHD)0.40.20-0.2-0.4-0.6-0.8-11/12/2005 0:00 6/12/2005 0:00 11/12/2005 0:00 16/12/2005 0:00 21/12/2005 0:00 26/12/2005 0:00 31/12/2005 0:00Figure 6-22 HD Validation – Water Levels – Fishing Coop – December 2005G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-181.210.80.6Site 2 (Evans River Entrance) - MHL Temporary RecorderRecordedModelledWSE (m AHD)0.40.20-0.2-0.4-0.6-0.8-11/12/2005 0:00 6/12/2005 0:00 11/12/2005 0:00 16/12/2005 0:00 21/12/2005 0:00 26/12/2005 0:00 31/12/2005 0:00Figure 6-23 HD Validation – Water Levels – Site 2 – December 20051.210.80.6Site 11 (Tucombil Canal Upstream) - MHL Temporary RecorderRecordedModelledWSE (m AHD)0.40.20-0.2-0.4-0.6-0.8-11/01/2006 0:00 6/01/2006 0:00 11/01/2006 0:00 16/01/2006 0:00 21/01/2006 0:00 26/01/2006 0:00 31/01/2006 0:00Figure 6-24 HD Validation – Water Levels – Site 11 – January 2006G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-19Site 9 (Brandy Arm Entrance) - MHL Temporary RecorderRecordedModelled1.210.80.6WSE (m AHD)0.40.20-0.2-0.4-0.6-0.8-11/01/2006 0:00 6/01/2006 0:00 11/01/2006 0:00 16/01/2006 0:00 21/01/2006 0:00 26/01/2006 0:00 31/01/2006 0:00Figure 6-25 HD Validation – Water Levels – Site 9 – January 20061.2Iron Gate - MHL Permanent RecorderRecordedModelled10.80.6WSE (m AHD)0.40.20-0.2-0.4-0.6-0.8-11/01/2006 0:00 6/01/2006 0:00 11/01/2006 0:00 16/01/2006 0:00 21/01/2006 0:00 26/01/2006 0:00 31/01/2006 0:00Figure 6-26 HD Validation – Water Levels – Iron Gate – January 2006G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-201.210.80.6Site 5 (Iron Gates Downstream) - MHL Temporary RecorderRecordedModelledWSE (m AHD)0.40.20-0.2-0.4-0.6-0.8-11/01/2006 0:00 6/01/2006 0:00 11/01/2006 0:00 16/01/2006 0:00 21/01/2006 0:00 26/01/2006 0:00 31/01/2006 0:00Figure 6-27 HD Validation – Water Levels – Site 5 – January 20061.210.80.6Fishing Coop - MHL Permanent RecorderRecordedModelledWSE (m AHD)0.40.20-0.2-0.4-0.6-0.8-11/01/2006 0:00 6/01/2006 0:00 11/01/2006 0:00 16/01/2006 0:00 21/01/2006 0:00 26/01/2006 0:00 31/01/2006 0:00Figure 6-28 HD Validation – Water Levels – Fishing Coop – January 2006G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-211.210.80.6Site 2 (Evans River Entrance) - MHL Temporary RecorderRecordedModelledWSE (m AHD)0.40.20-0.2-0.4-0.6-0.8-11/01/2006 0:00 6/01/2006 0:00 11/01/2006 0:00 16/01/2006 0:00 21/01/2006 0:00 26/01/2006 0:00 31/01/2006 0:006.4.2.3 DiscussionFigure 6-29 HD Validation – Water Levels – Site 2 – January 2006The following key points are noted in relation to the HD validation of the model:• The phasing of the tidal signal is accurately reproduced by the model over the validation period;• In terms of amplitude, the model tends to underestimate peak levels by occasionally up to 0.1m.This represents about 7% of the average spring tide amplitude, and 12% of the average neaptide amplitude;• During a flood event, when the Tuckombil weir overflows into the Evans River estuary, the modelis still consistent with the recorded data. The discrepancies observed both in the amplitude (themodel predicts peak levels short by about 15cm at the upstream site) and in the duration and/orshape of the event are largely due to the quality of the weir flow data used as an input into theRMA model. This was previously discussed in Section 3.2.2. Notwithstanding this, the modelpredictions over this specific period replicate the recorded tidal signal quite reliably in thedownstream sections of the Evans River estuary. The model also returns to its tidal state in theupper section of the estuary after approximately 3 days, consistent with the recorded data.• As a summary, this validation exercise again confirms that, given the uncertainties associatedmainly with the catchment inflows and to some extent with the bathymetric data, the model isreproducing the major hydrodynamic features of the Evans River estuary. This model is thuswell suited for the purpose of this study.6.4.3 Model ContinuityThe RMA hydrodynamic model was also checked for any potential continuity issue. The followingapproach was implemented:• Input a default constant flow boundary of 10m 3 /s at the selected inflow locations. The inflowlocations were as per the catchment boundary inflows (see Figure 6-1);• Setup the ocean boundary as a constant value of 2m AHD;G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-22• Run the model over the HD calibration period (i.e. approximately 2.5 weeks); and• Check the model flow results across a number of selected sections along the length of theestuary. A total of 27 sections were selected, as shown in Figure 6-30. At each location, theerror between the predicted flow across the section and the expected flow (as the sum of allupstream inflows) was computed for each output timestep (i.e. every half hour). The average ofthese errors was then computed and is reported in Table 6-2.This table shows that for all sections the predicted flow is within 5% of the expected flow, with thiserror being less than 1% at about half of the locations. This is consistent with generalrecommendations and it shows that the model is not artificially creating and/or losing water. Hence, itensures the continuity of the model predictions.Table 6-2Results of the RMA Model Continuity CheckProfileAverageError1 0.4%2 0.6%3 0.7%4 0.9%5 1.1%6 4.6%7 1.3%8 1.0%9 1.2%10 0.8%11 2.8%12 0.6%13 0.8%14 0.8%15 1.5%16 1.1%17 0.7%18 1.1%19 0.7%20 0.9%21 0.8%22 0.9%23 1.0%24 2.4%25 1.4%26 1.8%27 3.0%G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-246.4.4 Advection Dispersion CalibrationTo accurately capture advection and dispersion, the model requires input of dispersion coefficients.These coefficients determine the resultant spread of dissolved material throughout the model domain.RMA provides several methods for applying the dispersion coefficient, many of which wereinvestigated in this study. BMT WBM typically uses the Elder approach, and this was given firstpriority in this study. With the Elder formula, the dispersion coefficient is locally approximated byrelating it proportionally to the product of the channel depth and depth-averaged velocity. The userspecifies the term of proportionality for the RMA model.It was found, however, that this parameterisation was unable to capture salt recovery sufficiently well.Without investigating this result in detail, it is surmised that it is related to the reliance of the Elderapproach on accurate simulation of detailed velocity fields, which was potentially difficult in theshallow and transient regions of the Evans River estuary where bathymetric and hydrodynamicfeatures are likely to occur at scales smaller than the model element size. It is noted that BMT WBMstaff were unable to navigate vessels in these sections at certain times of the tide and as suchcomparing with data in these regions was not possible. Collection of detailed survey as part of futurework may be desirable to eliminate this possibility in more detailed analyses.As a result, and after testing a range of parameterisations, the dispersion coefficients within themodel framework were assigned to be constant on a local level within differentiable hydrodynamicand sediment type areas. The primary delineation in this regard was the transition point of the mainchannel from sands to muds at approximately the Council Site 2 sampling location (see Figure 2-19),and the dispersion coefficients were varied spatially to reflect this. In particular, the dispersioncoefficients in the lower and upper reaches were set to 20, and 0.1 m 2 /s, respectively. These aregenerally consistent with expected literature values, with the lower value reflecting the ‘choking’ effectof the upper estuary (in terms of pollutant dispersal) as a result of dominant wetting and drying,generally shallow waters and the potential associated flow constrictions.6.4.4.1 Calibration DataSalinity data from the Council monitoring program was used to calibrate the salt recovery rates in theRMA model over the period July 2006 to December 2006. Details of this program are presented inSection 2.6.2.Model salinity concentrations were varied with time at the tidal boundary based on measured salinityat Site 5 near the breakwater. Catchment flows were assigned a salt concentration of zero, with theexception of overflowing water from the Tuckombil weir where conductivity data from the RockyMouth Creek station was applied. This assumption was deemed of sufficient accuracy for thepurpose of the current study. However, further investigations into the weir overflows, both in terms ofwater quantity and water quality is recommended if considerations beyond the current study level arenecessary in future assessments.The dates for which data were used for AD calibration are 21/7/2006 to 31/12/2006. During thisperiod there were inflow events, with associated flushing and salinity recovery evident in the Councildata, thus allowing for calibration of the AD model.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-25Results of the AD model calibration are presented in the following section.6.4.4.2 Calibration Results – Salt RecoveryCatchment inflows from storm events will flush estuary systems of saline water to varying degreesdepending on the size of the storm and hydrodynamics of the system. The calibration of the ADmodel was based on evaluating recovery of salinity after storm events that flushed the system entirelyor almost entirely with fresh rainwater. This would ensure the rate of recovery is a function ofadvection and dispersion alone, with salt being pumped up-estuary from the mouth at a ratedetermined by natural dispersive processes. This recovery rate has been used to estimatedispersion coefficients for calibration of the AD model.Figure 6-31 through Figure 6-35 show the salinity in the estuary with respect to time at the Councilsampling locations (as shown in Figure 2-19) together with model predictions.RVC Recording Site 1454035Salinity (PSU)30252015105ModeledRecorded021/07/06 10/08/06 30/08/06 19/09/06 09/10/06 29/10/06 18/11/06 08/12/06 28/12/06Date (2006)Figure 6-31 AD Calibration – Salinity – Council Site 1G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-26RVC Recording Site 2454035Salinity (PSU)30252015105ModeledRecorded021/07/06 10/08/06 30/08/06 19/09/06 09/10/06 29/10/06 18/11/06 08/12/06 28/12/06Date (2006)Figure 6-32 AD Calibration – Salinity – Council Site 2RVC Recording Site 3454035Salinity (PSU)30252015105ModeledRecorded021/07/06 10/08/06 30/08/06 19/09/06 09/10/06 29/10/06 18/11/06 08/12/06 28/12/06Date (2006)Figure 6-33 AD Calibration – Salinity – Council Site 3G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-27RVC Recording Site 4454035Salinity (PSU)30252015105ModeledRecorded021/07/06 10/08/06 30/08/06 19/09/06 09/10/06 29/10/06 18/11/06 08/12/06 28/12/06Date (2006)Figure 6-34 AD Calibration – Salinity – Council Site 4RVC Recording Site 5454035Salinity (PSU)30252015105ModeledRecorded021/07/06 10/08/06 30/08/06 19/09/06 09/10/06 29/10/06 18/11/06 08/12/06 28/12/06Date (2006)6.4.4.3 DiscussionFigure 6-35 AD Calibration – Salinity – Council Site 5The model accurately reproduces the behaviour of estuary flushing as a result of two consecutivestorm events and subsequent recovery over a multi-month period. Council sites 3 through 5demonstrate rapid recovery because of the proximity to the mouth of the Evans River. Recovery atSites 1 and 2 is slower. This behaviour is typical of such a small and well-flushed estuary.The model slightly underestimates the salinity at the sites near the tidal boundary even though thesalinities defined at the tidal boundary were equal to the salinities measured at the Council samplinglocation near the mouth of the Evans River. This may be due to local sub-element scale effects notG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

HYDRODYNAMIC MODELLING 6-28captured in the model. In general, however, the model is performing well in terms of its ability tocapture salt recovery and hence is suitable for application to the advection dispersion study.6.4.5 Assumptions and LimitationsKey assumptions and limitations of the RMA10S modelling and calibration are summarised asfollows:• The bathymetric form of the Evan River estuary is known to be time variant. This has not beencaptured in the modelling framework, but rather our best estimate of the bathymetry has beenused, based on reference to all appropriate and available data sources. As such, the bathymetryof the system at the times where hydrodynamic and water quality data were collected may notnecessarily match the bathymetry adopted in the modelling framework. Future works couldconsider detailed and targeted bathymetric survey to complement further hydrographic and waterquality surveys to overcome this limitation;• Uncertainty associated with bathymetry is believed to contribute to the differences in modelledand measured salinity values at the most upstream location because of the diminished amountof tidal advection available given it is a shallow, isolated system in that region.• Catchment model discharges are uncalibrated because catchment drainages are not gauged.WaterCAST is accurate at predicting catchment discharge subject to the assumptions supportingthe model. All appropriate measures were taken to minimise the number and magnitude ofunvalidated assumptions; and• There are uncertainties associated with weir flows, including quantity and water qualitycharacteristics, as discussed above, and again these could be examined as part of future works.• Weir overflows were given salinity values that were recorded at the upstream Rocky MouthCreek recording station, however, it is believed these had little (if any) affect on the calibrationdue to the relatively small salt concentrations observed at this station.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-17 STP DISCHARGE SCENARIOS7.1 Discharge AlternativesDischarge to the Evans River estuary was evaluated for five different discharge locations, withpotentially time-varying discharges:• Continuous 24-hour STP discharge via one of three diffusers in the lower Evans River estuaryincluding one single port outfall option;• As above, but for ebb-tide discharges only; and• Discharges from wetland and carbon sequestration forest located at two positions in the estuary.7.1.1 Continuous and Ebb DischargeFigure 7-1 shows the three locations selected for the continuous and ebb-tide discharge locations asdetermined in consultation with Council. Multiport diffusers were evaluated at the bridge andentrance discharge location for continuous and ebb-tide discharges, and a single, open pipe wasevaluated for continuous and ebb-tide discharges on the northern breakwater revetment wall.Figure 7-2 shows the daily effluent flow rate and Figure 7-3 shows the water quality for those effluentflow rates over the annual simulation period based on data provided by Council and Hydrosphere(2010).It was assumed that ebb-tide discharge occurs only when the tide is moving out of the estuary systemand that the discharge starts at the beginning of the ebb-tide period and discharges for 3 hours. Thetotal discharge time during a 24-hour period is approximately 6 hours. Due to the decreased windowfor discharge for the ebb-tide scenarios, instantaneous flows rates increase by a factor of 4 for theebb-tide discharge scenarios.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-345004000Continuous DischargeEbb-Tide Discharge35003000Flow Rate (kL/Day)2500200015001000500001/01 20/02 10/04 30/05 19/07 07/09 27/10 16/12Figure 7-2 Effluent Flow Rates (2008)40.035.0TN mg/LTP mg/L4.504.0030.025.03.503.00TN (mg/l)20.015.02.502.001.50TP (mg/l)10.01.005.00.500.001/01 20/02 10/04 30/05 19/07 07/09 27/10 16/120.00Figure 7-3 Weekly Effluent Water Quality (2008)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-47.1.2 Wetland / Forest DischargeFigure 5-4 shows the four locations selected for the wetland / forest discharge locations asdetermined in consultation with Council. Due to potential site feasibility issues with the downstreamdischarge locations, i.e. Doonbah and Iron Gates, these sites have not been considered further inscenario assessments completed in this section.Discharge flow rates varied from site to site and are shown in Figure 7-4 and Figure 7-5. It can beseen that flows are discharged periodically and correlate with significant catchment rainfall eventsand that there are no continual discharges from the sites. Discharge loads were assumed to bedirectly proportional to discharge flows. This is based on the application of an event meanconcentration (EMC) to all discharges. This approach was used to maintain consistency withcatchment modelling approaches (see Table 1 of Appendix D) and to overcome limitations of thewetland / forest models for predicting event based runoff quality. Wetland and forest flows and loaddeterminations are further discussed in Section 5.4.With STP Wetland / Scheme150.0Discharge (MLD)120.090.060.030.00.001/01 01/02 01/03 01/04 01/05 01/06 01/07 01/08 01/09 01/10 01/11 01/12Existing150.0Discharge (MLD)120.090.060.030.00.001/01 01/02 01/03 01/04 01/05 01/06 01/07 01/08 01/09 01/10 01/11 01/12Figure 7-4 Tuckombil Canal Wetland / Forest Discharge Flows (2008)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-580.0With STP Wetland / SchemeDischarge (MLD)64.048.032.016.00.001/01 01/02 01/03 01/04 01/05 01/06 01/07 01/08 01/09 01/10 01/11 01/1280.0ExistingDischarge (MLD)64.048.032.016.00.001/01 01/02 01/03 01/04 01/05 01/06 01/07 01/08 01/09 01/10 01/11 01/127.2 Modelling PeriodFigure 7-5 Brandy Arm Creek Wetland / forest Discharge Flows (2008)Discharge scenarios were set up and executed in RMA-10s using the calibrated model over theperiod of 1/1/2008 to 31/12/2008. This period was selected to ensure an overlap of effluent flow,effluent water quality data and ambient water quality data, and to allow for calculation of annual waterquality medians for assessment against water quality objectives. This time period was applied to all ofthe modelling scenarios.7.3 Modelled ConstituentsOnly nutrients were found to be in higher concentrations in the proposed discharge than in the EvansRiver (see discussion provided in Section 2.7). As such, the discharge constituents of concern formodelling were total nitrogen (TN) and total phosphorus (TP). As agreed at the study outset,RMA10s was configured to simulate only the fate and transport of passive tracers; the modelledscenarios do not account for pathogens or chlorophyll/algal species. The diluted values of thedischarged tracers were combined in post processing with ambient water quality measurements overthe simulation period to ascertain total water quality concentrations across the model.Each given discharge scenario will be assessed against relevant ANZECC guideline trigger values fornutrients given in Table 2-3. These values are stated as annual median concentrations. Someconsideration is given the distribution of the measured values and increased concentrations as aresult of the discharge scenarios compared to the background concentrations and the water qualityobjectives.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-67.4 Modelling FrameworkIn order to provide an internally consistent modelling framework, flows and concentrations deliveredto the RMA model were obtained directly from precursor CORMIX modelling of a diffuser system (inthe case of the non-wetland discharges), and this provided a clear conceptual link between the twomodelling scales. Discharges were delivered directly to the model in the case of the wetland / forestscenarios, in a manner consistent with general catchment flows.7.4.1 CORMIX ModellingCORMIX is USEPA approved and used mathematical modelling program employed for the analysis,prediction and design of pollutant discharge into various bodies of water. Initial dilution is the mixingof discharge into receiving waters as the result of the initial momentum of the discharge. The mixingmodelling performed pursuant to this water quality study was performed in accordance to themethods outlined in the CORMIX Users Manual (Doneker, 2007). Details are described in thefollowing subsections.7.4.1.1 InputsAmbient tidal conditions can greatly influence the dilutions predicted by CORMIX. As such, theCORMIX model set up in this study was forced with a range of tidal currents extracted from thecalibrated HD model. These were then used to develop a ‘lookup’ table of predicted near fielddilutions to force the AD model.To develop this matrix of dilution factors, ambient velocities were separated into representativevelocities groups around the 10 th , 25 th , 50 th , 75 th , and 90 th percentile velocities. Table 7-1 summarisesthese velocities by discharge location.Table 7-1Ambient Velocity CategorisationDischargeLocationEntranceBridgeRevetmentWallVelocityAmbient VelocityPercentile ContinuousEbb-tideRange m/s m/sGroup0-25 0.047 0.056 125-50 0.103 0.125 250-75 0.175 0.217 375-90 0.260 0.324 490-100 0.355 0.418 50-25 0.042 0.051 125-50 0.089 0.092 250-75 0.149 0.144 375-90 0.212 0.202 490-100 0.267 0.253 50-25 0.061 0.074 125-50 0.131 0.146 250-75 0.218 0.239 375-90 0.308 0.332 490-100 0.384 0.412 5In addition to background current speed, CORMIX also requires specification of river channelgeometry of average depth, average width and depth of water at discharge to account for channelG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-7irregularity. Average water depths and widths were assumed based on the lowest water surfaceelevation of the model. This is conservative as dilution decreases with average depth. Table 7-2provides these values for the two diffuser discharge locations.Table 7-2Ambient Channel GeometryCORMIX Parameter Entrance Bridge a Revetment WallTide Elevation (m AHD) -0.70 -0.68 -0.70Average Depth (m) 2.7 3.3 2.4Average Width (m) 50 50 72Depth at Discharge (m) 3.5 3.3 3.1a – note that that the bridge site is roughly formed by two channels separated by a middle sand shoal,conservatively the width of one side has been used.Receiving water density was calculated based on an average ambient temperature of 20°C andsalinity of 37.2 ppt. Density was calculated at 1026.5 kg/m 3 .CORMIX also requires specification of discharge flow rate as this can influence near field dilutionsconsiderably. Effluent flow rates provided by Council (in Hydrosphere, 2010) were divided into 4groups from the minimum value of 1.75 million litres per day (MLD) to 3.90 MLD in a similar mannerto that of ambient velocity categorization. These groups and corresponding categories are given inTable 7-3. The maximum daily discharge rate for the ebb-tide scenarios was 2.50 MLD.Table 7-3Effluent Flow Rate CategorizationFlow Continuous Ebb-TideRange (MLD) Group Group3.94 - 3.58 13.59 - 2.86 22.86 - 2.13 3 12.13 - 1.76 4 2Ebb-tide discharge only occurs 5-7 hours per day, which will result in a higher hourly flow rate for thisdischarge alternative, even though the daily flow rate might be the same. CORMIX requires aninstantaneous flow rate rather than a daily flow rate. For the CORMIX modelling, the temperature ofthe effluent was assumed to be 25°C.7.4.1.2 Diffuser ConfigurationBridge and EntranceThe outfall configuration used in the CORMIX modelling was a deeply submerged three port diffuser(each port 100 mm diameter). The diffuser length varied from 10 to 20 metres and the diffuser wasassumed to sit on the bottom of the channel perpendicular to the direction of the currents. Diffuserports were oriented downstream at a vertical angle of 30 degrees incident to the bottom of thechannel. Port elevation was 0.5 m above the manifold. The same diffuser configuration was used forboth ebb-tide and continuous discharges. Refer to conceptual arrangements provided in Figure 8-1and Figure 8-2.Because of the distance between ports on the diffuser and because CORMIX schematises multiportdiffusers as 2-dimensional slots of length identical to the length of the diffuser, the diffuser wasactually modelled as a deeply submerged single port outfall with one-third of the overall discharge.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-8This is deemed valid because the jets do not interact with each other within the distance of the nearfield and each port discharge behaves as a single port discharge prior to reaching the boundary ofthe near field.Discharge velocities of the outfall (i.e. at each nozzle) based on the effluent flow rate groupingsdiscussed previously are provided in Table 7-4.Revetment WallThis outfall configuration assumes an open 170mm diameter pipe extending approximately 1 metrehorizontally from the revetment of the north breakwater 3 . The outfall would be located near the bottomof the deepest part of the channel in this area. Effluent would discharge into the channelperpendicular to the current direction in most tidal conditions. Refer to conceptual arrangementprovided in Figure 8-3.Table 7-4Diffuser Discharge VelocitiesContinuousGroupDischargeVelocity (m/s)Ebb TideGroupMultiport Diffuser1 1.93 1 4.912 1.58 2 3.463 1.234 0.86DischargeVelocity (m/s)Single Port Outfall1 2.00 1 5.082 1.63 2 3.573 1.274 0.897.4.2 RMA Modelling – Combination MethodOnce the CORMIX modelling was completed for the range of scenarios described above, predictionsfor near field flow rates and dilutions were inserted into the AD model. This ensured consistency ofpredictions between the two modelling paradigms.In particular, the range of tidal currents, discharge flow rates and discharge qualities were allsimulated in CORMIX to provide a three dimensional ‘lookup’ table to affect this insertion into the ADmodel, where the CORMIX results were called on dynamically by AD model to alter the inserted flowrate and constituent concentrations. Specifically, total nitrogen and phosphorus concentrations weredelivered to the AD model as separate passive tracers (normalised against their respective maximumconcentrations across the simulation period), as were the predicted hydraulic flows, at the edge of thenear field mixing zone.Ebb-tide discharges were simulated in an identical fashion to continuous discharges, with theexception of the time frame of discharge.The time series or normalised tracer and hydraulic flow computed for continuous and ebb-tidesrelease within CORMIX were then used as input into AD model as an element inflow.3 A single port arrangement was selected at this site as it represented the simplest type of discharge arrangement andwould provide a useful comparison to the more complex diffuser arrangement selected for the entrance site.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-9In contrast to the above, wetland / forest discharges were assumed to enter the model as any othercatchment inflow would, without the need for CORMIX modelling.7.5 Results7.5.1 CORMIXTable 7-5 summarises the CORMIX near field modelling results showing dilution factors. Near fieldlengths are on the order of 4 to 17 metres, which is within the typical element size of the model mesh.The results in Table 7-5 show that the highest effluent flow rate and lowest ambient velocity providethe least amount of dilution, and the lowest effluent flow rate and highest ambient velocity provide thegreatest amount of dilution. This is consistent with expectations. The ebb-tide discharge dilutionfactors are less than the continuous discharge dilution factors because the ebb-tide discharge flowrate is approximately 4 times the continuous discharge flow rate, and larger flow rates result in poorerdilution performance for a given diffuser configuration.Table 7-5CORMIX Dilution Factor Reference MatrixDischargeMethodSite 1 - EntranceContinuousEbb-tideSite 2 - BridgeContinuousEbb-tideEffluentGroupSite 3 - Revetment WallContinuousEbb-tideCORMIX Dilution FactorAmbient Velocity Group1 2 3 4 51 28.8 52.2 98.1 147.9 195.92 24.1 41.8 73.9 111.3 148.63 22.3 36.6 61.1 91.3 122.34 21.6 33.6 53.3 78.6 105.51 17.5 21.9 27.1 38.5 48.52 15.7 19.2 22.7 31 38.71 25.6 40.5 73.2 108.4 136.22 23.8 33.6 55.9 81.6 102.83 23.1 30.2 47 67.2 84.54 18.2 22.1 41.7 58.3 72.91 15.9 18.2 21.4 23.3 28.12 14.4 16.3 18.6 19.8 23.21 13.4 22 25.1 35.7 42.62 11.9 15.6 21 29.8 35.83 11.7 14.8 19 26.9 32.34 11.6 14.3 17.9 25.3 30.31 8 12.3 21.9 30.7 48.92 8.8 6.4 21.6 29.9 35.57.5.2 Advection-Dispersion Model7.5.2.1 Data Extraction LocationsFigure 7-6 shows the locations of the points for model data extraction. These are noted to extendacross the estuary. A location outside of the estuary on Airforce Beach has also been selected forinterrogation.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-117.5.2.2 Continuous and Ebb-Tide ResultsFigure 7-7 through Figure 7-19 show the continuous and ebb-tide discharge results. Because modelresults fluctuate with tidal cycles, results for all discharge scenarios were filtered into daily maximumvalues for easier comparison between discharge locations and discharge scenarios.All discharge results are presented as a change in concentration above the backgroundconcentrations of total nitrogen and total phosphorus. That is, the results shown in the figures areconstituent concentrations from the effluent discharge only, and do not account for ambientconcentrations. Impact to ambient concentrations will be discussed subsequent to this section.0.0600.050Continuous EntranceContinuous BridgeContinuous RevetmentEbb Tide EntranceEbb Tide BridgeEbb Tide RevetmentModelled scenario results represent increases in concentrationsonly, not total concentrations including background values.Total Nitrogen (mg/L)0.0400.0300.0200.0100.00001/01 01/03 30/04 29/06 28/08 27/10 26/12Figure 7-7Continuous and Ebb-Tide Discharge, Point 2 (Tuckombil Canal), Total Nitrogen(2008)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-120.0600.050Continuous EntranceContinuous BridgeContinuous RevetmentEbb Tide EntranceEbb Tide BridgeEbb Tide RevetmentModelled scenario results represent increases in concentrationsonly, not total concentrations including background values.0.040Total Nitrogen (mg/L)0.0300.0200.0100.00001/01 01/03 30/04 29/06 28/08 27/10 26/12Figure 7-8 Continuous and Ebb-Tide Discharge, Point 4, Total Nitrogen (2008)0.0600.050Continuous EntranceContinuous BridgeContinuous RevetmentEbb Tide EntranceEbb Tide BridgeEbb Tide RevetmentModelled scenario results represent increases in concentrationsonly, not total concentrations including background values.0.040Total Nitrogen (mg/L)0.0300.0200.0100.00001/01 01/03 30/04 29/06 28/08 27/10 26/12Figure 7-9 Continuous and Ebb-Tide Discharge, Point 5, Total Nitrogen (2008)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-130.0600.050Continuous EntranceContinuous BridgeContinuous RevetmentEbb Tide EntranceEbb Tide BridgeEbb Tide RevetmentModelled scenario results represent increases in concentrationsonly, not total concentrations including background values.0.040Total Nitrogen (mg/L)0.0300.0200.0100.00001/01 01/03 30/04 29/06 28/08 27/10 26/12Figure 7-10 Continuous and Ebb-Tide Discharge, Point 6, Total Nitrogen (2008)0.0600.050Continuous EntranceContinuous BridgeContinuous RevetmentEbb Tide EntranceEbb Tide BridgeEbb Tide RevetmentModelled scenario results represent increases in concentrationsonly, not total concentrations including background values.Total Nitrogen (mg/L)0.0400.0300.0200.0100.00001/01 01/03 30/04 29/06 28/08 27/10 26/12Figure 7-11 Continuous and Ebb-Tide Discharge, Point 7, Total Nitrogen (2008)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-140.0600.050Continuous EntranceContinuous BridgeContinuous RevetmentEbb Tide EntranceEbb Tide BridgeEbb Tide RevetmentModelled scenario results represent increases in concentrationsonly, not total concentrations including background values.Total Nitrogen (mg/L)0.0400.0300.0200.0100.00001/01 01/03 30/04 29/06 28/08 27/10 26/12Figure 7-12 Continuous and Ebb-Tide Discharge, Point 8 (Entrance), Total Nitrogen (2008)0.0600.050Continuous EntranceContinuous BridgeContinuous RevetmentEbb Tide EntranceEbb Tide BridgeEbb Tide RevetmentModelled scenario results represent increases in concentrationsonly, not total concentrations including background values.Total Nitrogen (mg/L)0.0400.0300.0200.0100.00001/01 01/03 30/04 29/06 28/08 27/10 26/12Figure 7-13 Continuous and Ebb-tide Discharge, Beach Point, Total Nitrogen (2008)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-150.0100.008Continuous EntranceContinuous BridgeContinuous RevetmentEbb Tide EntranceEbb Tide BridgeEbb Tide RevetmentModelled scenario results represent increases in concentrationsonly, not total concentrations including background values.Total Phosphorus (mg/L)0.0060.0040.0020.00001/01 01/03 30/04 29/06 28/08 27/10 26/12Figure 7-14 Continuous and Ebb-Tide Discharge, Point 2 (Tuckombil Canal), TotalPhosphorus (2008)0.010Continuous EntranceContinuous BridgeContinuous RevetmentEbb Tide EntranceEbb Tide BridgeEbb Tide Revetment0.008Modelled scenario results represent increases in concentrationsonly, not total concentrations including background values.Total Phosphorus (mg/L)0.0060.0040.0020.00001/01 01/03 30/04 29/06 28/08 27/10 26/12Figure 7-15 Continuous and Ebb-Tide Discharge, Point 4, Total Phosphorus (2008)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-160.010Continuous EntranceContinuous BridgeContinuous RevetmentEbb Tide EntranceEbb Tide BridgeEbb Tide Revetment0.008Modelled scenario results represent increases in concentrationsonly, not total concentrations including background values.Total Phosphorus (mg/L)0.0060.0040.0020.00001/01 01/03 30/04 29/06 28/08 27/10 26/12Figure 7-16 Continuous and Ebb-Tide Discharge, Point 5, Total Phosphorus (2008)0.0100.008Continuous EntranceContinuous BridgeContinuous RevetmentEbb Tide EntranceEbb Tide BridgeEbb Tide RevetmentModelled scenario results represent increases in concentrationsonly, not total concentrations including background values.Total Phosphorus (mg/L)0.0060.0040.0020.00001/01 01/03 30/04 29/06 28/08 27/10 26/12Figure 7-17 Continuous and Ebb-Tide Discharge, Point 6, Total Phosphorus (2008)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-170.0100.008Continuous EntranceContinuous BridgeContinuous RevetmentEbb Tide EntranceEbb Tide BridgeEbb Tide RevetmentModelled scenario results represent increases in concentrationsonly, not total concentrations including background values.Total Phosphorus (mg/L)0.0060.0040.0020.00001/01 01/03 30/04 29/06 28/08 27/10 26/12Figure 7-18 Continuous and Ebb-Tide Discharge, Point 7, Total Phosphorus (2008)0.0100.008Continuous EntranceContinuous BridgeContinuous RevetmentEbb Tide EntranceEbb Tide BridgeEbb Tide RevetmentModelled scenario results represent increases in concentrationsonly, not total concentrations including background values.Total Phosphorus (mg/L)0.0060.0040.0020.00001/01 01/03 30/04 29/06 28/08 27/10 26/12Figure 7-19 Continuous and Ebb-Tide Discharge, Point 8 (Entrance), Total Phosphorus (2008)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-180.0100.008Continuous EntranceContinuous BridgeContinuous RevetmentEbb Tide EntranceEbb Tide BridgeEbb Tide RevetmentModelled scenario results represent increases in concentrationsonly, not total concentrations including background values.Total Phosphorus (mg/L)0.0060.0040.0020.00001/01 01/03 30/04 29/06 28/08 27/10 26/12Figure 7-20 Continuous and Ebb-tide Discharge, Beach Point, Total Phosphorus (2008)It is noted that during continuous discharge, effluent is observed to migrate up the estuary becausedischarge occurs during flood tide conditions as well as ebb-tide conditions. Even for ebb-tidedischarges, effluent may be observed to migrate up the estuary. This phenomenon is likely to occurduring neap tide events (for ebb-tide releases) due to the diminished “flushing” from lower ebb-tidevelocities which does not allow effluent to fully escape from the estuary, prior to being reintroduced onthe next flood tide event.To illustrate the effect of effluent being conveyed differently through the estuary on different tides,Figure 7-21 shows incremental increases in TN for a continuous entrance discharge during springtide and neap tide events on 27 th July and 3 rd August 2008.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-190 hr8 hr flood0 hr8 hr flood2 hr ebb10 hr flood2 hr ebb10 hr flood4hr ebb12 hr flood4hr ebb12 hr flood6 hr ebb14 hr ebb6 hr ebb14 hr ebbFigure 7-21 Incremental TN Concentrations Resulting from Continuous Release at Entrance - Neap Tide 27 July 2008 (left), Spring Tide 3 August 2008 (right)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-20The colouring within the images represents the incremental increases in TN concentrations resultingfrom the STP discharge. The dark blue shading (most commonly shown) represents the minimumincremental TN concentration of 0.005mg/L above background concentrations (incremental increasebelow 0.005 mg/L have not been shown). The model had been running for the entire year of data(i.e. since 1/1/2008) prior to this data being extracted, and hence the model was sufficiently ‘warmedup’. The images show:• For both neap and spring tides, the incremental TN concentrations at the boundary are less than0.005 mg/L (as the images do not show discharges reaching the model boundary inconcentrations greater than this). Hence artificial losses of TN over the model boundary arelikely to be negligible. The ocean boundary selected appears to have been suitably located forthe purposes of these assessments;• An ebbing tide (i.e. outgoing tide) is unable to remove the entire TN mass within the estuary outto the ocean. Hence, this mass of TN is moved backward and forwards through the estuaryacross the ebbing and flooding tide; and• Spring tides result in greater distribution of the effluent throughout the upper estuary and out intothe ocean (when compared to a neap tide) as a result of the stronger tidal currents experiencedduring spring tides.Results for discharges on the ebb-tide were similar to those for the continuous release except thatless effluent gets conveyed upstream of the discharge point. However, some effluent does getconveyed upstream despite it being discharged from the estuary on the ebb-tide, a proportion returnsfrom the ocean on the next flooding tide.Data Extraction and Comparison to WQOsThe Council water quality data presented in Section 2.6.2 already demonstrate exceedences ofmedian concentrations of the ANZECC water quality objective for total nitrogen and phosphorus inthe upper reaches of the Evans River estuary. Further water quality data is presented in Section 3.5and in particular Figure 3-10, Figure 3-11 and Figure 3-12 identify water quality conditions in theestuary during that year.Comparisons between modelled results and background ambient concentrations (calculated asmedian values over 2008) were performed using the maximum value of modelled daily maximumsduring a two-week period around each Council sampling event in 2008. Predicted concentrationincreases were combined with ambient measurements on a volumetric dilution basis to provide totalpoint concentrations for comparison with water quality objectives. This was undertaken on a sampleby sample basis rather than a time-series basis as there were significant gaps in the measured datathat precluded time-series-style combination. Results for ebb-tide and continuous release examplesare included in Table 7-6 and Table 7-7.Figure 7-22 through Figure 7-25 show box plot distributions of the background ambient (i.e. year2008) water quality and the increases above background predicted by the model dischargescenarios. Similar to the data provided in Figure 2-20, the whiskers extend for 1.5 times the interquartilerange (unless maximum or minimum data values lay within this range and they then form theend of the whiskers). If maximum or minimum values lie outside of the range of the whiskers, theyare shown on the graph.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-21Table 7-6Median Concentrations and Modelled Increases for Continuous DischargesData ExtractionLocation andDischarge OptionMeasured BackgroundConcentrationTNmg/LTPmg/LIncremental ConcentrationIncrease bTNmg/LTPmg/LPredicted ResultantConcentrationTNmg/LWQO 0.30 0.03 Default Trigger Values for Estuary Ecosystem aData Extraction Point 1Background 0.675 0.060TPmg/LEntrance 0.007 (1%) 0.000 (0%) 0.682 0.060Bridge 0.009 (1%) 0.000 (0%) 0.684 0.060Revetment 0.008 (1%) 0.000 (0%) 0.683 0.060Data Extraction Point 2Background 0.635 0.028Entrance 0.007 (1%) 0.000 (0%) 0.642 0.028Bridge 0.010 (2%) 0.000 (0%) 0.645 0.028Revetment 0.009 (1%) 0.000 (0%) 0.644 0.028Data Extraction Point 3Background 0.635 0.028Entrance 0.011 (2%) 0.000 (0%) 0.646 0.028Bridge 0.015 (2%) 0.001 (4%) 0.650 0.029Revetment 0.014 (2%) 0.000 (0%) 0.649 0.028Data Extraction Point 4Background 0.430 0.030Entrance 0.016 (4%) 0.000 (0%) 0.446 0.030Bridge 0.023 (5%) 0.000 (0%) 0.453 0.030Revetment 0.019 (4%) 0.000 (0%) 0.449 0.030Data Extraction Point 5Background 0.250 0.025Entrance 0.010 (4%) 0.000 (0%) 0.260 0.025Bridge 0.016 (6%) 0.001 (4%) 0.266 0.026Revetment 0.013 (5%) 0.001 (4%) 0.263 0.026Data Extraction Point 6Background 0.250 0.025Entrance 0.011 (4%) 0.000 (0%) 0.261 0.025Bridge 0.021 (8%) 0.001 (4%) 0.271 0.026Revetment 0.016 (6%) 0.001 (4%) 0.266 0.026Data Extraction Point 7Background 0.155 0.025Entrance 0.022 (14%) 0.001 (4%) 0.177 0.026Bridge 0.039 (22%) 0.002 (8%) 0.194 0.027Revetment 0.030 (21%) 0.002 (8%) 0.185 0.027Data Extraction Point 8Background 0.155 0.025Entrance 0.021 (14%) 0.001 (4%) 0.176 0.026Bridge 0.034 (22%) 0.002 (8%) 0.189 0.027Revetment 0.033 (21%) 0.002 (8%) 0.188 0.027WQO 0.12 0.025 Default Trigger Values for Marine Ecosystem aData Extraction Beach Point 1Background NA c NA cEntrance 0.014 0.001 NA NABridge 0.012 0.001 NA NARevetment 0.013 0.001 NA NAValues in bold indicate concentrations in excess of objective(a) ANZECC 2000(b) Percentage increases were determined by dividing the incremental increase by the measured backgroundconcentration(c) No existing monitoring data available for the beach zone suitable to establish background conditionsG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-22Table 7-7Median Concentrations and Modelled Increase for Ebb-Tide DischargesData ExtractionLocation andDischarge OptionMeasured BackgroundConcentrationTNmg/LTPmg/LIncremental ConcentrationIncrease bTNmg/LTPmg/LPredicted ResultantConcentrationTNmg/LWQO 0.30 0.03 Default Trigger Values for Estuary Ecosystem aData Extraction Point 1Background 0.675 0.060TPmg/LEntrance 0.005 (1%) 0.000 (0%) 0.680 0.060Bridge 0.006 (1%) 0.000 (0%) 0.681 0.060Revetment 0.005 (1%) 0.000 (0%) 0.680 0.060Data Extraction Point 2Background 0.635 0.028Entrance 0.006 (1%) 0.000 (0%) 0.641 0.028Bridge 0.007 (1%) 0.000 (0%) 0.642 0.028Revetment 0.006 (1%) 0.000 (0%) 0.641 0.028Data Extraction Point 3Background 0.635 0.028Entrance 0.009 (1%) 0.000 (0%) 0.644 0.028Bridge 0.011 (2%) 0.000 (0%) 0.646 0.028Revetment 0.009 (1%) 0.000 (0%) 0.644 0.028Data Extraction Point 4Background 0.430 0.030Entrance 0.010 (2%) 0.000 (0%) 0.440 0.030Bridge 0.013 (3%) 0.000 (0%) 0.443 0.030Revetment 0.011 (3%) 0.000 (0%) 0.441 0.030Data Extraction Point 5Background 0.250 0.025Entrance 0.007 (3%) 0.000 (0%) 0.257 0.025Bridge 0.011 (4%) 0.000 (0%) 0.261 0.025Revetment 0.008 (3%) 0.000 (0%) 0.258 0.025Data Extraction Point 6Background 0.250 0.025Entrance 0.007 (3%) 0.000 (0%) 0.257 0.025Bridge 0.018 (7%) 0.001 (4%) 0.268 0.026Revetment 0.010 (4%) 0.000 (0%) 0.260 0.025Data Extraction Point 7Background 0.155 0.025Entrance 0.013 (8%) 0.001 (4%) 0.168 0.026Bridge 0.052 (34%) 0.003 (12%) 0.207 0.028Revetment 0.022 (14%) 0.001 (4%) 0.177 0.026Data Extraction Point 8Background 0.155 0.025Entrance 0.014 (9%) 0.001 (4%) 0.169 0.026Bridge 0.040 (26%) 0.002 (8%) 0.195 0.027Revetment 0.040 (26%) 0.002 (8%) 0.195 0.027WQO 0.12 0.025 Default Trigger Values for Marine Ecosystem aData Extraction Beach Point 1Background NA c NA cEntrance 0.014 0.001 NA NABridge 0.013 0.001 NA NARevetment 0.013 0.001 NA NAValues in bold indicate concentrations in excess of objective(a) ANZECC 2000(b) Percentage increases were determined by dividing the incremental increase by the measured backgroundconcentration(c) No existing monitoring data available for the beach zone suitable to establish background conditionsG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-237.5.2.3 Effect of Reduced Discharge Periods for Ebb-Tide DischargesModelling runs were completed with different total ebb-tide discharge periods including 10 hours and6 hours. The 6 hour (total) discharge period has been presented within this report. The effect of thereduced discharge period included:• Slightly improved (i.e. lower predicted increases in TN and TP concentrations) in the sectionsupstream of the discharge location, by up to 1%; and• Slightly worsened (i.e. higher predicted increases in TN and TP concentrations) in the sectionsdownstream of the discharge location, by up to 5%.Conceptually this makes sense, as the discharge period decreases more effluent is being pusheddownstream on the ebb-tide and potentially out to the ocean where it will not return, hence decreasedwater quality is likely to be experienced downstream of the discharge location, and improvedconditions upstream.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-24Figure 7-22 Total Nitrogen, Continuous Discharge ImpactsG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-25Figure 7-23 Total Nitrogen, Distribution of Ebb-tide Discharge ImpactsG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-26Figure 7-24 Total Phosphorus, Distribution of Continuous Discharge ImpactsG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-27Figure 7-25 Total Phosphorus, Distribution of Ebb-tide Discharge ImpactsG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-287.5.2.4 Wetland / Forest ResultsThe results identified for the wetland / forest schemes are influenced primarily by the forestdischarges, as the wetland rarely overflows direct to the estuary.Typically forest discharges occur after rainfall events which exceed available soil moisture stores inthe forest soils. It has been determined that the irrigation of the forest with STP effluent allowsoptimum forest growth/biomass as the forest growth is not limited by water supply and opportunitiesto take up water are greater than in an existing forest in the same location. The resultant higherevapo-transpiration rate reduces the volume of water available for runoff or deep drainage and alsoreduces the frequency of soil saturation meaning it takes a larger rainfall event to trigger surfacerunoff.This effect is likely to reduce the flow and hence load of forest derived pollutants (as these areproportional to the magnitude of event based runoff) that will be discharged to the estuary. Figure 7-4and Figure 7-5 shows total flows to the estuary for selected wetland / forest schemes over 2008. Thenet result is shown in Figure 7-26.40,00030,000Net Flow Difference Brandy ArmNet Flow Difference Tuckombil Canal20,000Runoff kL/day10,0000-10,000-20,000-30,000-40,000Figure 7-26 Net Wetland / Forest Runoff for Selected SchemesG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-29Differences in flows and pollutant loads associated with the implementation of the wetland / forestschemes across 2008 are shown in Table 7-8.Table 7-8 MEDLI Predicted Reductions in Runoff and Pollutant Loads, 2008Wetland Site Flow (ML) TN (Tonne) TP (kg)Brandy Arm Difference -138 -0.21 -8Tuckombil Canal Difference -197 -0.29 -8It can be seen that smaller flow reductions occur from the Brandy Arm wetland / forest site than fromthe Tuckombil Canal wetland / forest site, while roughly equivalent reductions across the year areobserved for total nutrient loads. Table 7-9 includes predicted WaterCAST flows and loads to theupper and entire estuary across the same period. The upper estuarine catchment (upstream of theconfluence of Brandy Arm Creek with the Evans River) is approximately 23km 2 , while the totalcatchment area is approximately 92 km 2 . The forest area of the wetland / forest is approximately 1.25km 2 .Table 7-9 WaterCAST Predicted Upper and Total Catchment Loads, 2008Site Flow (ML) TN (Tonne) TP (Tonne)Upper Estuary 55,000 48.5 8.2Entire Estuary 98,000 104.4 12.6Proportionally it can be seen that the net incremental changes in loads as a result of the wetland /forest schemes are small in comparison to total and upper estuary contributions across the sameperiod. This is further represented in Figure 7-27 which shows the net flow information presented inFigure 7-26 against predicted catchment runoff to the upper estuary over the same period.Comparison of Upper Catchment Flows to Net Wetland / Forest Runoff40,00030,000Net Flow Difference Brandy ArmNet Flow Difference Tuckombil CanalCatchment Flows (Upper Estuary)12,000,0009,000,000Net Wetland Runoff (kL/day)20,00010,0000-10,000-20,0006,000,0003,000,0000-3,000,000-6,000,000Upper Catchment Flows (kL/day)-30,000-9,000,000-40,0002/01/2008 1/02/2008 2/03/2008 2/04/2008 2/05/2008 2/06/2008 2/07/2008 1/08/2008 1/09/2008 1/10/2008 1/11/2008 1/12/2008 31/12/2008-12,000,000Figure 7-27 Comparison of Upper Catchment Flows to Net Wetland / Forest RunoffG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-30Figure 7-27 shows the relatively minor nature of the reduced flows in relation to the scale of the uppercatchment discharges. For larger runoff events, any potential flow (and load) reduction to the estuarywould be negligible in comparison to the large amount generated from the remainder of thecatchment. However, for smaller more frequent rainfall/runoff events the reductions in flows andloads to the estuary may be more significant and it may influence resultant water quality in theestuary (i.e. result in minor reductions in nutrient concentrations as these nutrients are being capturedin the forest).To investigate this further, modelling of incremental changes in concentrations of total nutrients in theEvans River as a result of runoff from the wetland / forest schemes have been conducted using theadvection-dispersion model.To overcome limitations of the AD model in assessing the changes resulting from “negative” flowsand loads from the wetland / forest schemes, the approach adopted has been to model the total flowsand loads to the estuary for the existing case and with the wetland / forest scheme implemented inthe AD model. Subsequent to this, the predicted incremental increased in total nutrients weresubtracted from each other at both sites, to provide a resultant figure, which is indicative of the totalnutrient concentration reductions which may be achieved. The results provided by this method areconsidered indicative and full water quality modelling (including use of calibrated catchment loads)would be required to accurately model incremental water quality improvements.The outcomes of this modelling are presented in Figure 7-28 through Figure 7-33. It can be seenfrom these figures that there is a predicted reduction in total nutrient concentrations throughout(mainly) the upper estuary with effects being barely noticeable downstream of Data Extraction Point 3(hence no figures have been included for sites downstream of this point. The effects are mostnoticeable at the Tuckombil Canal site, primarily due to the reduced tidal exchange experienced atthis site.Predicted resultant total nutrient concentrations are presented Table 7-10 (a further description ofmethods used to develop this table has previously been provided in Section 7-11). It should benoted that there is some “noise” in this table in that there are some higher percentage reductionspredicted downstream of Site 6. These results should be ignored. This noise is due to smallrounding errors in model output and the actual magnitude of the predicted reductions is negligible.Figure 7-28 and Figure 7-29 show box plot distributions of the background ambient (i.e. year 2008)water quality and the changes in background predicted by the model discharge scenarios.Similar to the data provided in Figure 2-20, the whiskers extend for 1.5 times the inter-quartile range(unless maximum or minimum data values lay within this range and they then form the end of thewhiskers). If maximum or minimum values lie outside of the range of the whiskers, they are shownon the graph.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-310.30Tuckombil CanalBrandy Arm Creek0.200.10Total Nitrogen(mg/L)0.00-0.10-0.20Modelled scenario results represent increases in concentrations only,not total concentrations including background values.-0.3001/01 31/01 01/03 01/04 01/05 01/06 01/07 31/07 31/08 30/09 31/10 30/11 30/12Figure 7-28 Wetland / Forest Discharge, Point 1 (Upstream), Total Nitrogen (2008)0.30Tuckombil CanalBrandy Arm Creek0.200.10Total Nitrogen(mg/L)0.00-0.10-0.20Modelled scenario results represent increases in concentrations only,not total concentrations including background values.-0.3001/01 31/01 01/03 01/04 01/05 01/06 01/07 31/07 31/08 30/09 31/10 30/11 30/12Figure 7-29 Wetland / Forest Discharge, Point 2, Total Nitrogen (2008)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-320.30Tuckombil CanalBrandy Arm Creek0.200.10Total Nitrogen(mg/L)0.00-0.10-0.20Modelled scenario results represent increases in concentrations only,not total concentrations including background values.-0.3001/01 31/01 01/03 01/04 01/05 01/06 01/07 31/07 31/08 30/09 31/10 30/11 30/12Figure 7-30 Wetland / Forest Discharge, Point 3, Total Nitrogen (2008)0.03Tuckombil CanalBrandy Arm Creek0.020.01Total Phosphorus(mg/L)0.00-0.01-0.02Modelled scenario results represent increases in concentrations only,not total concentrations including background values.-0.0301/01 31/01 01/03 01/04 01/05 01/06 01/07 31/07 31/08 30/09 31/10 30/11 30/12Figure 7-31 Wetland / Forest Discharge, Point 1 (Upstream), Total Phosphorus (2008)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-330.03Tuckombil CanalBrandy Arm Creek0.020.01Total Phosphorus(mg/L)0.00-0.01-0.02Modelled scenario results represent increases in concentrations only,not total concentrations including background values.-0.0301/01 31/01 01/03 01/04 01/05 01/06 01/07 31/07 31/08 30/09 31/10 30/11 30/12Figure 7-32 Wetland / Forest Discharge, Point 2, Total Phosphorus (2008)0.03Tuckombil CanalBrandy Arm Creek0.020.01Total Phosphorus(mg/L)0.00-0.01-0.02Modelled scenario results represent increases in concentrations only,not total concentrations including background values.-0.0301/01 31/01 01/03 01/04 01/05 01/06 01/07 31/07 31/08 30/09 31/10 30/11 30/12Figure 7-33 Wetland / Forest Discharge, Point 3, Total Phosphorus (2008)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-34Table 7-10Median Concentrations and Modelled Results for Wetland / Forest DischargesData ExtractionLocation andDischarge OptionMeasured BackgroundConcentrationTNmg/LTPmg/LIncremental ConcentrationIncrease b cTNmg/LTPmg/LPredicted ResultantConcentrationTNmg/LWQO 0.3 0.03 Default Trigger Values for Estuary Ecosystem (a)Data Extraction Point 1Background 0.675 0.060TPmg/LTuckombil Canal -0.068 (-10%) 0.000 (0%) 0.607 0.060Brandy Arm Ck -0.002 (0%) 0.000 (0%) 0.673 0.060Data Extraction Point 2Background 0.635 0.028Tuckombil Canal 0.000 (0%) -0.001 (-4%) 0.635 0.027Brandy Arm Ck -0.013 (-2%) 0.000 (0%) 0.622 0.028Data Extraction Point 3Background 0.635 0.028Tuckombil Canal 0.000 (0%) 0.000 (0%) 0.635 0.028Brandy Arm Ck -0.008 (-1%) 0.000 (0%) 0.627 0.028Data Extraction Point 4Background 0.430 0.030Tuckombil Canal 0.000 (0%) 0.000 (0%) 0.430 0.030Brandy Arm Ck -0.004 (-1%) 0.000 (0%) 0.426 0.030Data Extraction Point 5Background 0.250 0.025Tuckombil Canal -0.004 (-2%) 0.000 (0%) 0.246 0.025Brandy Arm Ck -0.003 (-1%) 0.000 (0%) 0.247 0.025Data Extraction Point 6Background 0.250 0.025Tuckombil Canal -0.005 (-2%) 0.000 (0%) 0.245 0.025Brandy Arm Ck -0.003 (-1%) 0.000 (0%) 0.247 0.025Data Extraction Point 7Background 0.155 0.025Tuckombil Canal 0.000 (0%) 0.000 (0%) 0.155 0.025Brandy Arm Ck -0.003 (-2%) 0.000 (0%) 0.152 0.025Data Extraction Point 8Background 0.155 0.025Tuckombil Canal -0.007 (-5%) 0.000 (0%) 0.148 0.025Brandy Arm Ck -0.003 (-2%) 0.000 (0%) 0.152 0.025WQO 0.12 0.025 Default Trigger Values for Marine Ecosystem (a)Data ExtractionBeach Point 1Background NA d NA dTuckombil Canal 0.000 0.000 NA NABrandy Arm Ck 0.000 0.000 NA NAValues in bold indicate concentrations in excess of objective(a) ANZECC 2000(b) Percentage increases were determined by dividing the incremental increase by the measured backgroundconcentration(c) Modelling approach adopted for wetland / forest scheme provides indicative results(d) No existing monitoring data available for the beach zone suitable to establish background conditionsG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-35Figure 7-34 Total Nitrogen, Distribution of Wetland / Forest Discharge ImpactsG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-36Figure 7-35 Total Phosphorus, Distribution of Wetland / Forest Discharge ImpactsG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

STP DISCHARGE SCENARIOS 7-377.6 Summary of FindingsPresented below are key findings of this component of work:• Nutrient concentrations downstream of each discharge location are generally increased abovethose in the upstream direction, as a result of tidal action (i.e. tidal exchange or flushing) carryingeffluent out of the estuary;• Ebb-tide discharges generally result in higher nutrient concentrations in the downstream directionand lower in the upstream direction, as more effluent is pushed towards the ocean on the ebbingtide, as opposed to continuous discharges which allow a greater proportion of effluent to carryupstream;• Predicted resultant TN concentrations increases/decreases are larger than those for TP, as thereare lower loads/concentrations of TP in the treated effluent being discharged via the ebb-tidecontinuous and wetland options;• A number of sites (mainly in the upper estuary) recorded ambient water quality conditions inexcess of the identified guideline trigger values. This outcome was independent of whether STPdischarges were included or not;• Discharges from the bridge results in larger increases in TN and TP at all data extraction points,than discharges at the entrance / revetment wall for both ebb-tide and continuous discharges.Discharges at entrance and revetment wall sites results in more rapid dispersion because of theimmediate mixing with the larger body of ocean water. Ebb-tide discharge demonstrates greaterdispersion as a result of the dose and rest cycling, allowing for the same amount of dispersion inthe absence of discharge during rest periods;• The greatest increase above background concentrations for the continuous and ebb-tide optionsis for an ebb-tide discharge from the bridge, which was calculated to be approximately 0.052mg/L TN at Data Extraction Point 7 (~ 34% above ambient conditions at that location). Thisoption also provided the greatest increase in TP concentrations which was determined to be0.003 mg/L (~ 12% above ambient conditions at that location);• Predicted resultant TN concentration increases in the mid to upper estuary (i.e. upstream of DataExtraction Point 5) indicates minor predicted nutrient increases of less than 6% abovebackground ambient concentrations for both ebb-tide and continuous releases;• In line with the effect of the wetland / forest scheme reducing net flows (and consequentlypollutant loads) to the estuary, modelling results suggest that there are some potential reductionsin TN concentrations in the far upper estuary (i.e. Data Extraction Point 1) for the TuckombilCanal wetland / forest. Negligible reductions in ambient nutrient concentrations were predictedas a result of the implementation of Brandy Arm wetland / forest; and• There is insufficient available background water quality data for the beach location to predict aresultant concentration, however, in terms of incremental increases the wetland / forestdischarge provided no discernable increase at the beach, while the ebb-tide and continuousreleases (from all discharge locations) provided minor increases of up to 0.014 mg/L TN and0.001mg/L TP.Further discussion of these findings is presented in Section 8.1.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-18 DISCHARGE SCENARIO IMPACT RISK ASSESSMENTSThis section presents an impact risk assessment of STP discharge scenarios considered in thisstudy. The impact risk assessment aims to address questions posed by Council which includeidentification of:• The ability of the Evans River estuary to accept and assimilate or dissipate STP effluentdischarges; and• The impact of STP discharges on the environmental and social values of the Evans Riversystem.In addition to these criteria, physical constraints influencing scenario constructability and operabilityhave been reviewed. Cost of scenarios was not required to be assessed as part of this study.8.1 Water QualityThis study has placed significant focus on assessing water quality responses related to the estuarinedischarges of STP effluent. As such, the modelling completed as part of this investigation provides avaluable insight into the likely water quality effects of various STP discharge scenarios.In terms of the pollutants considered as part of the study, the study has focused on total nutrients (i.e.nitrogen and phosphorus) as the concentrations of total nutrients in the discharge are significantlyhigher than background ambient concentrations and also higher than ANZECC guideline triggervalues.Further consideration of other potential pollutants in the STP effluent has not been pursued at thisstage. This decision was based on a preliminary review of available STP effluent discharge qualityinformation which identified that other potential pollutants such as total suspended solids, faecalcoliforms, biological oxygen demand and pH in the discharge were better than existing ambientconditions within the estuary and/or were within already within acceptable ANZECC guideline triggervalues (if available for that pollutant). Hence, these potential pollutants were deemed to be a low riskto estuarine water quality conditions (refer to Section 2.7).Furthermore the discharge of freshwater into the lower estuary from ebb-tide and/or continuousrelease options was not considered to present a risk to estuarine water quality (in terms of reducedsalinity) due to the very high rates of dilution (i.e. ratio of STP effluent volume to daily tidal exchangevolumes) experienced in this section of the estuary, even during low tidal velocities. Discharges offreshwater from the wetland / forest will occur at times when surrounding catchment areas will also bedischarging freshwater to the estuary in response to rainfall events. As such the additional impact ofthe wetland / forest discharge would be negligible.The advection-dispersion models developed for scenario assessments simulate the fate andtransport of total nitrogen and total phosphorus (assumed to be conservative tracers). The limitationsof the approach include:• the models do not account for the various nutrient species that are components of the totalnutrient load (i.e. proportions of inorganic and organic nutrient, etc);G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-2• the models do not account for nutrient transformation and processing, via settling, biologicaluptake, interaction with sediments, etc; and• the models do not account for chlorophyll/algal species generation, etc.These limitations prevent more definitive assessments of potential water quality impacts and wouldrequire the development of more sophisticated modelling tools, supported by further water qualitytesting for the purposes of model calibration and validation.Section 7 provides an assessment of the potential water quality response within the estuary as aresult of the various discharge options assessed. Further discussion of these results is provided inthe following subsections.8.1.1 Continuous and Ebb-tide Release OptionsContinuous ReleaseThe findings of the assessments completed for the continuous release options identified that theseoptions will result in an increase in total nutrient concentrations (nitrogen more than phosphorus) atdata extraction points which traverse the estuary, and at the beach location outside of the estuary.This outcome is a function of tidal movements which move treated effluent through and out of theestuary. Figure 7-21 demonstrates the effect of tide moving effluent throughout the estuary andoffshore.The movement of effluent throughout the estuary means that circumstances could arise where thedischarge results in modelled concentrations exceeding the guideline trigger values. This is to saythat prior to the discharge, a site may have had ambient water quality conditions below the guidelinetrigger value; however, with the introduction of the effluent, the pollutant concentrations increase andthen exceed the guideline trigger value. This was not noted to occur at any site within the estuary forthe assessments completed as part of this study, although the assessments were focused on oneyear, i.e. 2008.The modelling showed that the magnitude of the increase varied throughout the estuary. Allcontinuous release options were to the lower estuary, correspondingly the greatest modelledincreases in nutrients occurred in this location. However, better (i.e. lower) ambient nutrientconcentrations and increased tidal exchange in the lower estuary mitigates the impacts of thedischarge. The estuary in this zone is able to assimilate nutrients without exceeding the guidelinetrigger values.Modelling indicates that continuous releases in the lower estuary results in increased nutrientconcentrations in the upper estuary. However, the magnitude of the increase is less than thatobserved in the lower estuary as less effluent gets conveyed to the upper estuary by tidal exchange.Increases in this zone increase the risk of adverse ecological impacts as existing median nutrientconcentrations already exceed the ANZECC guideline trigger values. Using the ANZECC guidelinetrigger values as the benchmark 4 for scheme acceptability, then continuous release options to thelower estuary are likely to present an unacceptable risk to estuarine water quality.4ANZECC (2000) guidelines pg 3.1-17 state, “recommend guideline trigger values, which represent bioavailable concentrations orunacceptable levels of contamination … If exceeded, these values trigger the incorporation of additional information or further investigationto determine whether or not a real risk to the ecosystem exists and, where possible, to adjust the trigger values into regional, local or sitespecificguidelines.”G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-3It should be noted that the magnitude of the increases in total nutrients is small and is typically lessthan 5% above background ambient levels. Further assessment work, outside the scope of thisstudy, would need to be completed to determine potential biological responses as a result of thisincrease in total nutrient concentrations.Outside of the estuary, data was extracted from a beach location. Incremental increases of 0.012 to0.014 mg/L TN and 0.001 mg/L TP were determined for this location. Due to the limitation of nothaving sufficient background water quality data for the beach location, it has not been possible todetermine the total modelled concentrations of TN or TP at this location sufficient to allow comparisonto ANZECC guideline trigger values.Ebb-tide ReleaseOverall, the modelling results of the ebb-tide release are similar to those of the continuous releases.However, the use of ebb tide discharges was found to result in:• Slightly improved (i.e. lower predicted increases in TN and TP concentrations) in the sectionsupstream of the discharge location. With the incremental reductions reaching up to 6% of thebackground ambient concentration at Data Extraction Point 7; and• Slightly worsened (i.e. higher predicted increases in TN and TP concentrations) in the sectionsdownstream of the discharge location. With the incremental increases reaching up to 8% of thebackground ambient concentration at Data Extraction Point 7.Conceptually these results makes sense, as the discharge period decreases significantly for the ebbtidedischarge, more effluent is being pushed downstream on the ebb-tide, hence decreased waterquality is likely to be experienced downstream of the discharge location, and improved conditionsupstream.8.1.2 Wetland / Forest Release OptionsThe findings of the assessment completed for the wetland / forest discharge scenarios identified thatthe implementation of the wetland / forest leads to increased evapo-transpiration (ET) rates (i.e. therate at which water is taken up by evaporation and transpiration). This occurred as a result of theforest having a constant water supply. This effect increased soil moisture deficits (i.e. amount ofrainfall that could be stored prior to runoff) and consequently reduced the volume and frequency ofoverflow events to the estuary. Reductions in volume of overflow events reduce the load of nutrientsdelivered to the estuary, compared to a similar forested area on the same soil profile.Modelling results indicate that there are some potential reductions in total nutrient concentrations inthe upper estuary for the Tuckombil Canal wetland, and .minimal potential reductions in ambientnutrient concentrations as a result of the Brandy Arm wetland. Full water quality modelling usingcalibrated catchment loads and flows is required to refine estimates of the magnitude of thereductions.Further considerations in respect of the wetland / forest discharges relate primarily to site availabilityand suitability, which have been outside of the scope of this study. The currently assessed option isG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-4of considerable size and sufficient land area would need to be identified. Further assessments ofthese sites would need to be made in respect of:• The connectivity between shallow groundwater beneath the forest site and the Evans Riverestuary;• The impact on long-term groundwater elevation of irrigation;• Potential groundwater impacts on receptors; and• Other social and environmental considerations.8.2 Physical Constraints Impacting on DischargeConstructabilityThis section provides a discussion of physical conditions at the sites of the proposed discharge, andin particular how these site characteristics may affect or impact on scheme constructability.The locations of the assessed ebb-tide and continuous release sites are shown in Figure 7-1. Table8-1 provides a discussion of key physical features at each discharge site.Table 8-1Key Physical Features at the Ebb-Tide and Continuous Release SitesDischargeMethodArrangementChannelWidth(m)Depth -ISLW toChannelBottom (m)Depth - ISLW toTop of Structure(m)Tidal ElevationRange a (mAHD)TidalVelocities b(m/s)Max FloodTideVelocity c(m/s)Site 1 -EntranceContinuous/ Ebb250mm pipe to 3port diffuser (each100mm diameter)positioned asshown in Figure 8-175 3.33 2.83 -0.90 to 1.100.18 Cont.0.22 Ebb1.16Site 2 - BridgeContinuous/ EbbSite 3 -RevetmentContinuous /Ebb250mm pipe to 3port diffuser (each100mm diameter)positioned asshown in Figure 8-2170mm single portdiffuser as shown inFigure 8-3105 1.47 0.97 -0.83 to 1.0880 2.64 2.14 -0.89 to 1.10(a) Tidal range of Indian Spring Low Water (ISLW) Tide to Higher High Water Summer Solstice(b) 50 to 75 th percentile velocities as per Table 7-1(c) Modelled flood velocities based on flood event Jan 20080.15 Cont.0.14 Ebb0.22 Cont.0.24 Ebb0.781.15Table 8-1 identifies relevant physical features of the discharge sites assessed, including channelwidth at the location of discharge, depth of water column from lowest tide (i.e. ISLW) to channelbottom and indicative depth from top of discharge infrastructure to lowest tide level (i.e. ISLW) at thedischarge location (for an assumed discharge arrangement). Furthermore, Table 8-1 includesestimates of tidal range (between ISWL and Higher High Water Summer Solstice), tidal velocities (for50 th to 75 th percentile of tides) and an estimate of maximum flood tide velocities at the dischargelocations. The information identifies a fairly clear relationship between channel width, depth andvelocities, as generally more constricted channels need to be deeper to convey similar quantities offlow. Also there is greater opportunity for morphological changes at the Entrance and Revetment wallsites as a result of the higher tides that are experienced in this zone.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-5It should be noted that information included in Table 8-1 represents a snapshot of conditions. Apartfrom channel width which is largely fixed at the discharge locations, the bathymetry of the estuary iscontinually changing in response to the actions of flood, tide and wave events. All other informationincluded in Table 8-1 is a function of channel (and entrance) bathymetry and will correspondingly varywithin a range of values over a given timeframe. Information in Table 8-1 is related to the estuaryconditions in 2006 (coincides with the date of the latest hydrosurvey and tide recording conducted byMHL). This needs to be considered in interpreting information included in Table 8-1.The conceptual arrangement of the pipeline and diffuser or outlet is shown in Figure 8-1, Figure 8-2and Figure 8-3. In providing these conceptual arrangements, no review/assessment of underlyinggeotechnical conditions or stability/structural capacity of the existing structures, e.g. breakwaters orbridge, has been made.It should be noted that CORMIX and RMA modelling of the bridge discharge was at a locationapproximately 25 m upstream of the Elm Street Bridge. The diffuser shown in Figure 8-2 is attachedto the downstream side of the bridge. It is not expected the difference in location will affect modellingresults.No arrangement has been presented for the wetland / forest discharge. It is expected that thisdischarge arrangement would be a single or series of shallow open drains/buried pipes to estuary,depending on the drainage characteristics and distance of the wetland / forest site to the estuary.The drain outlets would discharge to a stabilised discharge structure to prevent bank erosion. Pipes ifused would preferentially be buried to ensure pipe discharges occur below mean tide levels forimproved aesthetics. Some additional design and construction considerations include:• Pipe construction material would need to be cognisant of the typically saline conditions that canoccur in the upper estuary;• Consideration of the potential presence of acid sulphate soils would be required for anyexcavation work proposed; and• Provision of sufficient head to displace salt water from pipes will be a design consideration ifpipes are placed below the tide level.8.2.1 FloodsAs part of the Richmond River Flood Study (BMT WBM, 2010) the Evans River was included in themodel structure of the broader Richmond River, to allow for flood flows to be routed to the EvansRiver. The Evans River was added as a 1-dimensional section to the broader 2-dimensionalTUFLOW model of the Richmond River.Modelling recently completed included a 100 year average return interval, 72-hour flood with 100 yearstorm surge (2.0 m AHD). Model output from this ‘run’ has been interrogated to estimate potentialflood flows and velocities at the discharge locations assessed.The flood modelling identified that the entrance/revetment wall site had peak flows of nearly 1,400m 3 /s and peak flood velocities of 6.3 m/s, while the bridge site had peak flows of around 1,220 m 3 /sand peak velocities of around 1.27 m/s.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-6As can be seen from the flood modelling results there are significant differences in the peak floodvelocities between the discharge sites. The higher velocities in the entrance sites are due to theconstriction in the channel at this location. Higher velocities will contribute to higher shear stresseswhich would need to be accounted for in both the design of the mounting structure and diffuseroutlets.The high flood velocities will also contribute to significant quantities of bed erosion, potentiallyinfluencing discharge structure stability. Design will need to be cognisant of flood erosion potential ofthe discharge sites considered, particularly the Entrance site as this site is located in the entrancechannel which is subject to the highest flood discharge velocities in the estuary, and the infrastructureis not anchored against existing non-moveable structures such as the bridge or revetment wall.Estimated flood velocities for the 100-year event as discussed above, would not be the highestpossible, indeed more infrequent larger floods are possible as well. A suitable design flood event,plus safety margin would need to be determined for the purposes of later design.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

Not to Scale2.51.5Note: Information presented on bed levels is based onavailable hydrosurvey information and is subject to change inresponse to antecedent climatic conditionsHHW(SS) = 1.10 m AHD0.5Break WallElevation (m AHD)-0.5-1.5-2.5Discharge Pipe100mm PortsMLWS = -0.612 m AHDISLW = -0.897 m AHD-3.5-4.5-5.5Bed of EstuaryHHW(SS) = Higher High Water (Summer Solstice) ElevationM LWS = M ean Low Water Surface ElevationISLW = Indian Springs Low Water Elevation0.0 10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0 90.0Relative Distance (m)250mm DiffuserManif old0.5mTitle:Site 1Entrance Outfall Conceptual ArrangementBMT WBM endeavours to ensure that the information provided inthis map is correct at the time of publication. BMT WBM does notwarrant, guarantee or make representations regarding thecurrency and accuracy of information contained in this map.Filepath: I:\B17607_I_BRH Evans River DCC\PPT\PPT_001_100727 Site 1.pptxFigure:8-1Rev:Bwww.bmtwbm.com.au

Not to Scale2.51.5Note: Information presented on bed levels is based onavailable hydrosurvey information and is subject to change inresponse to antecedent climatic conditionsHHW(SS) = 1.083 m AHD0.5Pipe Attached toBridge PierMLWS = -0.549 m AHDElevation (m AHD)-0.5-1.5-2.5Bridge Pier100mm PortsISLW = -0.833 m AHD-3.5250mm DiffuserManif oldBed of Estuary-4.5 HHW(SS) = Higher High Water (Summer Solstice) ElevationM LWS = M ean Low Water Surface ElevationISLW = Indian Springs Low Water Elevation-5.530.0 50.0 70.0 90.0 110.0 130.0 150.0Relative Distance (m)Title:Site 2Bridge Outfall Conceptual ArrangementBMT WBM endeavours to ensure that the information provided inthis map is correct at the time of publication. BMT WBM does notwarrant, guarantee or make representations regarding thecurrency and accuracy of information contained in this map.Filepath: I:\B17607_I_BRH Evans River DCC\PPT\PPT_002_100727 Site 2B.pptxFigure:8-2Rev:Bwww.bmtwbm.com.au

Not to Scale2.51.5Note: Information presented on bed levels is based onavailable hydrosurvey information and is subject to change inresponse to antecedent climatic conditions0.5HHW(SS) = 1.099 m AHDElevation (m AHD)-0.5-1.5-2.5170mm SinglePort Outf allMLWS = -0.607 m AHDISLW = -0.892 m AHD-3.5Discharge Pipe0.5mBed of Estuary-4.5HHW(SS) = Higher High Water (Summer Solstice) ElevationM LWS = M ean Low Water Surface ElevationISLW = Indian Springs Low Water Elevation-5.530.0 40.0 50.0 60.0 70.0 80.0 90.0 100.0 110.0 120.0Relative Dis tance (m)Title:Site 3Revetment Outfall Conceptual ArrangementBMT WBM endeavours to ensure that the information provided inthis map is correct at the time of publication. BMT WBM does notwarrant, guarantee or make representations regarding thecurrency and accuracy of information contained in this map.Filepath: I:\B17607_I_BRH Evans River DCC\PPT\PPT_003_100727 Site 3.pptxFigure:8-3Rev:Bwww.bmtwbm.com.au

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-108.2.2 Commercial and/or Recreational InteractionEbb and Continuous ReleasesThe suggested locations for continuous and ebb-tide release points may provide some opportunity forcommercial or recreation interaction with them, although it is stressed that some of these interactionsmay present potential health and safety risks. The list below identifies some of the key types ofcommercial and recreational activities that may occur within the Evans River estuary and the types ofinteraction and associated risks:• Snorkelling – It is likely that during summer months snorkelling may be undertaken in sectionsof the lower estuary. Snorkelling undertaken in the vicinity of the discharges (providing claritywas sufficient) would allow individuals to see the discharge infrastructure. During dischargeperiod the discharge the plume is likely to be of low turbidity (high clarity) and may not be easilydetectable. There is some risk of water ingestion during snorkelling activities. Due to the depthof the outlet structures (>2m below the water surface) it is unlikely that any individual wouldcontact this infrastructure during snorkelling. The presence of the discharge infrastructure (ifvisible) may inspire the snorkelers to dive and make contact with it.• SCUBA Diving – It is unclear if much SCUBA diving is undertaken in the estuary. A similar setof circumstances exists as for snorkelling described above. The main difference may be that anindividual will dive to greater depths potentially providing greater opportunity forinteracting/touching the outlet infrastructure. The maximum velocities of the discharge would be~2 m/s. There is also the risk of skin contact with this infrastructure. The pipes may be heavilycovered in barnacles and other crustaceans presenting an abrasion risk. This risk iscommensurate with contact with other submerged infrastructures such as rocks, bridge piers,etc. If SCUBA diving is undertaken at times of high water clarity (which is normally the case)then discharge infrastructure may be visible.• Swimming – Swimming as opposed to snorkelling and SCUBA diving may be undertaken attimes of lower water clarity. Due to the depth of the outlet structures (>2m below the watersurface) it is unlikely that any individual would contact this infrastructure during normalswimming. However, there is some risk that diving off existing infrastructure, e.g. the bridge intothe water may allow an individual to contact the outlet structures. This may prevent a moreserious abrasion or impact risk. Appropriate design of the outlet to minimise this risk (i.e.recessing the outlets under the bridge to avoid this type of contact) and appropriate signage oreven jump prevention barriers may be required. The release infrastructure on the revetment wallor in the entrance are likely to be deeper than that at the bridge and as such provide a lower riskof contact. The discharge of STP effluent to the estuary may influence an individual’sperceptions of the cleanliness and safety of undertaking swimming within the estuary.• Fishing – There exists significant likelihood that fishing from shore or boats will interact withrelease infrastructure at any discharge location in the lower estuary. Generally this interactioncould involve tangled or hooked lines and anchors. The release infrastructure will be designed towithstand strong tide and flood flows and as such will be resistant to hooked lines, etc. Anglerswill learn where infrastructure is located by getting snagged and they will adjust their fishingbehaviour accordingly.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-11It is likely that crabbing is also undertaken within the estuary periodically, although it was notspecifically identified within previous studies, such as the Estuary Processes Study (PBP, 1999a)or Estuary Management Study and Plan (WBM, 2002) and crab pot markers were not notedduring field work undertaken within the estuary in early 2010.In respect of the consumption of cooked aquatic foods harvested from the estuary, effluentdischarges from the Evans Head STP are disinfected resulting in effluent with typically lowconcentrations of faecal coliforms (see Table 2-5). Assessment of potential pathogenic impactson fish and shellfish against accepted guidelines, e.g. ANZECC (2000) has not been completedas part of this current investigation, and should be considered as part of future detailedinvestigations.At present there are no known estuary based fishing businesses operating, e.g. fishing chartersor guided tours. However, it is possible that such activities do occur or may occur in the future.In terms of potential impacts on these ventures, general fishing impacts are outlined above andboating impacts are outlined below. In addition to these impacts, there may be perceivedimpacts of the effects of STP effluent discharges on the quantity and quality of fishing withinestuary and an individual’s desire to consume harvested seafood.• Recreational Boating (powered) – There are a variety of recreational boating craft that utilisethe Evans River estuary. Given the smaller size of the estuary most powered recreational craftare less than several metres in length and have drafts of less than 1.2 m (Watson, D. NSWMaritime, Pers. Comm., 2010). For the entrance and revetment discharge locations thesesmaller powered craft are unlikely to come into contact with release infrastructure as thereshould be at least 1.0 to 1.5m between the top of this infrastructure and the propeller during thelowest tidal event (ISLW). The outfall at the bridge may need to be accompanied by signageindicating potential hazard as there may not be any available distance between the propeller andthe top of the discharge structure (See Table 8-1). Depending on the risk of contact, NSWMaritime may require use of in-stream markers to indicate the locations of potential submergedhazards.• Recreational Boating (non-powered) – There are a number of non-powered vessels whichutilise the estuary including canoes, kayaks, windsurfers, row boats, etc. These vessels areexpected to have very small drafts of not more than around 0.3m. As such, these craft areunlikely to come into contact with release infrastructure and there should be at least a 0.6 mbetween the top of this infrastructure and these vessels during the lowest tidal event (ISLW) atthe bridge location, which sits the highest in the water.• Commercial Fishing Craft – While no commercial fishing is undertaken within the estuary,commercial fishing is undertaken offshore from the estuary. The Estuary Management Studyand Plan (WBM, 2002) identified that the Evans Head Boat harbour (located within the estuary)provides mooring for 25 boats, including (at that time) 11 trawlers, 13 trap and line fishing boatsand two tuna fishing boats. This report also identified that these fishing boats have bottomed-outon the bar causing leaks necessitating repairs, and that the entrance bar is a problem preventingtravelling boats utilising the boat harbour.Some of these vessels in the Evans Head Boat harbour are up 19 m long and have drafts in therange of 1.5 to 1.8 m (Watson, D. NSW Maritime, Pers. Comm., 2010). Hence, for the entrancedischarge location it is calculated that for the lowest tide (i.e. ISLW) that there would be aroundG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-120.8m freeboard between the bottom of deepest draft boat known to regularly cross the entranceand the top of the discharge infrastructure. Also, for the revetment wall site, there would bearound 0.3m clearance between the bottom of the deepest draft vessel known to regularlytraverse the entrance channel and the top of the discharge infrastructure on the lowest tide (i.e.ISLW tide). The revetment wall discharge point is close to the edge of the revetment wall andcould be identified with appropriate hazard channel markers to deter larger boats from travellingclose to this discharge infrastructure.While an argument may be posed that the deep draft vessels would not normally attempt a barcrossing on such a low tide, there remains a possibility that this may occur. The provision of0.8m clearance for the entrance site is based upon hydrosurvey information collected in 2006.The entrance conditions are dynamic and will vary according to tides and particularly large floodand wave events. There is insufficient information available to identify the range of bed depthswhich may occur at this site and further information is required to allow for a better estimate ofclearance, and hence risk to be made. Using the information at hand, the clearances predictedwould present a risk of contact with larger vessels, particularly if infrastructure was required to bebuilt further out of the bed than currently indicated.Larger commercial craft do not travel under the bridge, although signage indicating potentialhazards would be advisable.• Passive Recreation (walking, picknicking, etc) – The discharge of STP effluent is typicallyless turbid than the water in the Evans River, which at times (particularly during ebb-tidereleases) may create a visual difference between the discharge and the ambient water. Densitydifferences between the effluent, which is non-saline, and Evans River water, which is saline, willresult in effluent rising to the surface. Despite mixing that would occur with ambient flows, thedischarge will likely be visible at least part of the time due to the turbidity and density differencesbetween the effluent and Evans River water.Also the discharge plume might be visually apparent as a result of the momentum of thedischarge creating ripples on the surface of the water. Discharge velocities are likely to be toolow for this effect, however, at certain times, especially during periods of high discharge volumeand low water surface elevation, ripples may appear on the surface.STP effluent (i.e. tertiary treated wastewater) has a typical and distinctive odour (non-offensive tomost people). It is possible that the odour may be noticeable depending on the location of thedischarge and the discharge types (i.e. ebb or continuous). Of the discharge locationsconsidered, the revetment wall and bridge sites are immediately adjacent to where peopleregularly undertake passive recreation pursuits, and other pursuits such as fishing. The entrancedischarge site is also relatively close to commonly used recreational use areas. Of the dischargeoptions considered, continuous discharges will occur at times of slack tide, potentially presentingthe greatest opportunity for plumes to surface near these passive recreation locations.Assessment of the potential odour impacts of the discharge have not been assessed in detail aspart of this study. Subject to the outcomes of such investigations, these may influence schemepreferences, e.g. siting, release type, etc.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-13Wetland / Forest ReleasesThe wetland / forest release is likely to be a shallow gully drain, or a pipe discharge below the water.Discharges from the forest area to the estuary will typically only occur after significant wet periodsand as such the discharge is unlikely to be discernable from other existing discharges in the upperestuary. There is unlikely to be any residual treated effluent odours from the polished effluentoriginating from the forested areas. It is unlikely that the appearance of the water from the forestedareas would be discernable from other catchment discharges.A catchment discharge event was observed from the Woodburn Drain during a site inspection inMarch 2010. There was a discernable plume of turbid water and on occasions, highly discolouredwater coming from low lying lands upstream of the drain point as shown in Figure 8-4. The point ismade that the existing aesthetics of the area where the wetland / forest may be positioned mayalready be being impacted by existing catchment drainage infrastructure and the water dischargingthrough it.Figure 8-4 Discharges from Woodburn Drain, March 20108.2.3 Wave Conditions and Sand MovementAs documented in Section 3.1, there is expected to be a net ocean infeed of sand to the Evans River(not during flood years), although the exact rate was not quantified, and was recommended for furtherinvestigation in the Estuary Processes Study (PBP, 1999a). The extent of the penetration of thesematerials was identified to be at the approximate limit of ocean swells into the estuary, as thesefacilitate sand ingress on flooding tides. It was identified that the likely limit of swell penetration wasto where Woodburn Street meets the estuary (i.e. a few hundred metres downstream of the ElmStreet Bridge).G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-14Previous dredging activities in the lower estuary, below Elm Street bridge have been proven toprovide temporary navigation relief only, as both marine and fluvial sources would infill dredged areaswithin a reasonably short timeframe (PBP, 1999a).As such, it is likely that a highly active sand bed exists within the region from the entrance bar to thelimit of the entrance shoal which is downstream of the Elm Street Bridge. A major influence on theactivity of this shoal is wave climate / ocean swell which was identified to propagate to theapproximate upstream limit of the sand shoal, thereby defining its upstream extent.Wave conditions within the estuary are a function of ocean waves in the deepwater environmentoffshore and how they propagate to shore. MHL (as cited in GHD, 2006c) reported that there is adeepwater background wave climate in of the order of 1.6m wave height with a typical wave period of8-10 seconds offshore from Evans Head. Due to losses on the entrance bar, the nearshore waveclimate at the entrance of the Evans River is considerably reduced with average wave heights ofaround 0.5m penetrating the entrance. The Estuary Processes Study (PBP, 1999a) identified thatnorth easterly waves were present for up to 5% of the time, with the remainder presumablyemanating from the other directions, primarily the south-east.Based on tidal measurements completed by BMT WBM as part of this study, peak tidal velocitieswere recorded at the entrance (near the discharge sites ‘revetment wall’ and ‘entrance’). It was foundthat peak tidal velocities were 0.7 m/s on the spring tide, and 0.3 m/s on the neap tide. At a farupstream site, tidal velocities peaked at 0.45 m/s on the spring tide (see Section 2.3.2 for furtherinformation). These peak velocities are likely to exceed threshold velocities for bed load transportwhich typically occur in range of 0.1 to 0.3 m/s depending on the specifics of the bed sediments of theEvans River (i.e. particle sizes, roughness, etc).In addition to this, large floods can prevail in the estuary, particularly as the Evans River acts as aflood mitigation storage/outlet for floods from the Richmond River catchment. These flood eventscould scour significant amounts of bed materials from the Evans River entrance shoal. As outlined inSection 8.2.1, flood velocities will be up to 6 m/s for a 100 year flood event at the entrance. Floodvelocities of this magnitude will greatly exceed threshold velocities for bed load transport.Structures that may be built at the entrance site and revetment wall site will be need to be designed tobe resistant to the effects of sand and other sediment movement either through accretion as a resultof wave/tide mechanisms and via scour as a result of flooding. Resistance to these effects wouldneed to be achieved by:• Siting of outlets above the upper range of sand movement in the locations chosen;• Incorporating 1-direction (duckbill) valves to prevent sand (and saline water) ingress into thedischarge pipe; and• Ensuring discharge velocities are sufficient to open valve flaps and discharge any sands thatmay have become entrained in the discharge pipe.Similar processes should be adopted for the design of the structure on the Elm Street Bridge,although it is likely that the bed conditions are not as active at this location.It has not been possible to define potential bed level changes in the vicinity of the entrance.Suggested approaches for this include:G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-15• Review historical hydrosurvey information that may exist for the entrance including bathymetricsurveys and aerial photography (which provides an indication of shoal locations at differenttimes). The shortcoming of this approach is that there is no underlying knowledge of theconditions of the entrance area at the time of the surveys, i.e. was it subsequent to a scourevent, etc;• Create a morphological model across the entrance areas to predict sand movements (accretionand erosion) as a result of waves/tides accretion and flood erosion. It was noted that amorphological model was developed for the entrance by Manly Hydraulic Laboratory in 1997.The primary focus of this model was to assess impacts of tides on the entrance bar formation,however, it may be suitable for investigating shoaling rates at other locations within the estuary;and• Utilise existing local knowledge sources, e.g. unofficial observations of channel depth that mayhave been observed by long term commercial boat operators, or recreational fishermen, oragency staff, e.g. NSW Maritime, etc.Some earlier studies were completed which may also provide some historical information on thisaspect, including the 1986 Evans River Working Group, Evans River Siltation Study and 1993 PublicWorks Department, Evans River – North Coast Estuaries Sedimentological Studies. These studieswere not available for immediate review as part of this study.8.3 Operational ConsiderationsAs discussed in the previous section it is expected that there would be high rates of sedimentmovement in the entrance zone extending from the entrance bar (outside of the estuary breakwaters)to downstream of the Elm Street Bridge.In this zone, detailed estimates of maximum shoaling depths would need to be developed to allow forthe minimum height of the discharge infrastructure to be determined, e.g. outlet ports, etc. As thebridge is outside the zone of the active entrance shoal, shoaling rates should be reduced due to tidalinfluences. It is however, expected that changes can still occur as a result of flood events.The depth to which sand is entrained in the tide or flood flow will be dependent on the velocity of thewater and its ability to maintain this material in suspension. Observations of other estuaries on thenorth coast of NSW (during normal tidal conditions) have demonstrated that sand is mobilised atcertain locations, to the extent that it is visible at the surface. As such, it can be assumed that similarconditions could result at the Evans River estuary (mainly at the ‘revetment wall’ and ‘entrance’ sites).Consequently any outlet structure should be protected from sand ingress at these locations.Appropriate protection devices would necessarily be determined as part of the design process.Protection will be most relevant to ebb-tide release devices which do not have positive dischargevelocities at all times (as opposed to the continuous release options) preventing sand ingress.The type of device that may be used to prevent sand ingress would need to cognisant of thepotentially high rates of marine biological growth likely to occur on it. During field work completed byBMT WBM as part of this study, a variety of field data collection equipment was utilised. It wasobserved that after three weeks of deployment, a new foam marker ball was totally encrusted withbarnacles and was barely visible 0.5m below the water surface. This growth could lead to thefollowing types of outcomes:G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-16• Failure or reduced functionality, thereby allowing sand ingress; and• Reduced capacity of pipe outlet due to encrustation with barnacles.Design options for discharge infrastructure will need to be cognisant of these factors, and it may bepossible to design systems requiring lower levels of maintenance, i.e. due to use of materials whichresist marine growth, use of minor positive flows from the pipes (even during rest periods) whichprovide inhospitable conditions for marine organisms to establish, etc. Regardless of the approachadopted, regular maintenance programs would be required. These would likely require commercialdivers to access the outlet and ensure that outlet is operational. Indicative service periods would bequarterly.Saltwater ingress into the outlet structure may also occur. This may be an unacceptable outcomedepending on the materials used to construct the outlet structure and associated pipeline (most likelymild steel which is subject to corrosion from saltwater). The estuary is typically saline up to the tidallimit, so the potential impacts of saltwater ingress would apply wherever the structure is built.Design options to prevent saltwater ingress may include failsafe discharge closure structures, use ofmaterials highly resistant to corrosion, or the use of positive minor positive flows from the pipes (evenduring rest periods) to prevent saltwater ingress. The choice of closure devices should be cognisantof the likely high rates of biological growth likely to occur.8.4 Construction Considerations8.4.1 Terrestrial Pipeline from STPThe pipeline route from the STP to the various discharge locations would need to be confirmed aspart of a later investigation which reviews potential route options and the various social,environmental and economic implications associated with each option.It is noted that there are likely to be considerable differences in running a pipeline from the STP to thelower estuary versus one to the upper estuary for the wetland / forest option. Land ownership andassociated permitted uses of pipeline route lands would need to be considered in detail in any futurepipeline route assessments, as the STP is partly bounded by the Evans Head Memorial Aerodromeand Broadwater National Park. Also pipeline routes to the lower estuary are likely to pass extensivelythrough or adjacent to urban areas, while the wetland / forest option may (depending on the routeselected) be able to avoid these urban areas.GHD (2006b) includes a review of pipeline routes and associated construction issues between theEvans Head STP and a number of release sites in the lower estuary, roughly corresponding to theEntrance, Revetment wall and Bridge sites assessed in this study. This study identified pipelinelengths of between 3.2 and 4.5 km from the STP to the lower estuary.The wetland feasibility study (WCG, 2009) identified a 10km pipeline route length within their study toconvey treated STP flows to the wetland. A particular route was not identified in the study report.Pipeline route lengths are noted to vary by up to 6.8 km between the two release sites (i.e. lower andupper estuary), this is expected to considerably impact upon pipeline construction costs. Theterrestrial pipeline will, depending on the design adopted, probably need to be sunk further into theG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-17ground as it approaches the lower estuary to facilitate a connection to the marine pipeline sectionwhich connects it to the discharge infrastructure, as discussed further in the next section.Factors which will be relevant to a future assessment of pipeline routes may include:• Land ownership and associated use restrictions and access / approval requirements;• Pipeline lengths and implications for pumping, i.e. larger and greater numbers of pumps andassociated power usage;• Construction issues i.e. cultural heritage, noise, air quality, traffic, relocation of existing services,stormwater management, groundwater, acid sulphate soils, vegetation, etc; and• Operational issues, i.e. access for maintenance and repair, etc.8.4.2 Marine Pipeline and Discharge StructureThe approach taken to constructing the pipeline from the edge of the estuary to the dischargeinfrastructure would vary according to the prevailing geotechnical conditions and stability issuesassociated with existing infrastructure.For instance, it has been assumed that the pipeline to the discharge infrastructure on the bridge couldbe mounted onto the bridge. Further detailed structural and stability assessment would be requiredto ensure that this is indeed possible.Similarly approaches taken to route the pipeline to the discharge site ‘entrance’ which is in the middleof the channel will vary according to subsurface conditions through which the pipeline would need tolaid to reach this location. Assuming subsurface conditions are suitable, approaches such asHorizontal Directional Drilling (HDD) may be appropriate. Anchoring the diffuser at this location couldbe achieved with an appropriately sized concrete structure to provide weight and stability.The discharge site ‘revetment’ requires a pipeline to the northern revetment wall. A number ofapproaches could potentially be utilised to achieve this including trenching/jacking of the pipe andHDD. An important consideration for this option will be to ensure that any construction behind theexisting breakwater/revetment takes into account the pressure of the water on this wall, which may beincreased by wave swell hitting the wall. Also, some pile support and anchoring of the outfall at ornear the end of the pipe may be necessary to ensure stability and longevity of the structure.Of the discharge arrangements reviewed, it is likely the site ‘Entrance’ would provide the greatestengineering construction challenges. The pipeline to this site would need to be either routed alongthe breakwater or trenched along the main entrance channel to the diffuser location. No assessmentof the underlying geotechnical conditions or stability/structural capacity of the existing structures, e.g.breakwaters or bridge, has been possible as part of this study, and these factors are likely to be a keycriteria in determining the most cost effective and practical solution. Furthermore, works associatedwith the pipeline construction and diffuser may need to be executed from floating barges which will bein a location periodically subjected to small wave swell and tidal currents. The use of floating bargesand associated on board equipment may add significantly to the cost of a release structure in thislocation. There may be also added social impacts of these construction works as they will be highlyvisible and may prevent recreational and fishing boat egress to the ocean.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-188.5 Potential Ecosystem ResponsesThe introduction of non-saline STP effluent, containing relatively high concentrations of nutrients incomparison to background ambient conditions, into a mostly marine environment can impact waterquality and lead to associated biological / ecosystem responses. Previous sections discuss themodelled advection and dispersion of nutrients throughout the estuary and Section 3.7 identifiedpotential ecosystem responses.While not possible to determine biological responses as a part of this current investigation, there area number of potential biological responses which can be observed as a result of such a discharge,such as:• Increases in nutrient concentrations can lead to changes in macroinvertebrate species. Certainmacroinvertebrate species are sensitive to increased nutrient concentrations and would beunlikely to be present in zones of the estuary experiencing lower water quality.For the options assessed, there are predicted to be increases in nutrient concentrationsthroughout the estuary for the ebb-tide and continuous release scenarios. The resultantincreases in nutrients may lead to changes in macroinvertebrate communities. Modellingindicated that the largest magnitude of nutrient increases was in the lower estuary.• Increased nutrient concentrations can increase algal growth. Increased algal growth couldimpact on water quality through algal photosynthesis and respiration affecting diurnal dissolvedoxygen concentrations. Dieoff of algal blooms and associated bacterial decay could lead todeoxygenation of the water column potentially stressing fish and other benthic organisms.Excessive algal growth may increase water turbidity, reducing the depth to which light penetratesand hence impact on light dependent species, such as seagrass.For the options assessed, there are predicted to be increases in nutrient concentrationsthroughout the estuary for the ebb-tide and continuous release scenarios. Modelling indicatedthat the largest magnitudes of nutrient increases were in the lower estuary, however, resultantconcentrations were not shown to exceed the ANZECC guideline trigger values in this location.In the upper estuary where ambient concentrations already exceeded ANZECC guideline triggervalues there is potentially a greater risk of increased algal growth and associated impacts.• Flocculation of suspended sediments in STP discharges may lead to nutrient enrichment ofsediments. Discharges of non-saline STP effluent into saline environments may promote theflocculation of suspended material contained in the STP effluent. This flocculated material maysettle to the bed of the estuary and could potentially accumulate over time. If rates of nutrientrelease from the sediments is less than the rate at which new sediments are added, this maylead to an excess of nutrients in the sediments. The sediments over time could impact on thequality of surface water quality by liberation of nutrients.Modelling tools developed as part of this study were unable to identify potential risks associatedwith the nutrient enrichment of sediments.• Saltmarsh and mangrove and other water dependent littoral communities, including weedspecies may be able to access additional nutrients in the water column, as the ebb-tide andcontinuous release scenario were predicted to increase nutrient concentrations throughout theG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-19estuary. The magnitude of the predicted increases is largest in the lower estuary and lowest inthe upper estuary.8.6 Social and Environmental Value ImpactsFollowing on from a review of social and environmental values associated with the estuary (refer toSection 3.8); further assessment of the potential impacts of the discharge scenarios on identifiedsocial and environmental values is provided below:• Nature Conservation Values – Minor increases in nutrient concentrations have been predictedthroughout the estuary for ebb-tide and continuous release discharge scenarios (but not forwetland / forest scenario) thereby increasing the risk of a biological or ecosystem response, e.g.changes in macroinvertebrate community abundance and distribution, increased algal productionand associated risk of algal blooms, changes in trophic status of estuary, etc. These outcomes ifrealised could impact on identified nature conservation values and have longer term cumulativeimpacts on the estuary to support certain fish and bird populations. It would be prudent tocomplete further more detailed water quality modelling which can assess these implications. Ifsignificant impacts are identified in this regard, this would influence scheme feasibility.In addition to in-stream nature conservation values, the Evans River catchment itself has avariety of terrestrial flora and fauna values. The siting of the wetland / forest and associatedpipelines to this system or to lower estuarine discharge locations would need to be cognisant ofthese terrestrial values. Further assessments would need to be completed at a later stage in thesiting of this infrastructure depending on the scheme which is ultimately chosen for assessment.• Cultural and Heritage Values – Options leading to a noticeable biological response which affectthe health of the estuary may impact on cultural values and its role in food harvesting. There arelikely to be a number of cultural and heritage significant sites within the catchment which willneed to be considered in planning any pipeline route.• Education and Scientific Values – It is unlikely that the introduction of the STP effluent wouldsignificantly impact on the estuary’s education and/or scientific values. The siting of the wetland /forest and associated drainage infrastructure should be considerate of the location of thesubfossil coral reef and not give rise to direct or indirect impacts on this, i.e. direct damagethrough construction or enhanced bank erosion through poorly designed dischargeinfrastructure.• Scenic Values - It is possible that the bridge and revetment wall discharges (and possibly theentrance site) may on occasions be visible to the public either through the presence of surfaceripples, or via differences in water clarity/hue in the immediate vicinity of the discharge. Theseeffects would only be noticeable under certain conditions, i.e. certain low tides, clear ambientwater surrounding the discharge, etc. While not considered a major impact, these effects maylessen an individual’s appreciation of the estuary’s scenic values.The wetland / forest scheme will be far less evident to the general population and the likely effecton scenic values is considerably reduced.• Recreation and Tourism Values – Assessment completed as part of this investigation have notfocused on faecal contamination of the estuary. Generally, recreational water quality standardsand aquatic food standards relate to the degree of faecal contamination present withinG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-20waterways. Current performance data for the Evans Head STP (which is disinfected) indicatesthat there are low levels of faecal contamination within the discharge waters (generallyequivalent to or less than existing ambient background levels). However, further assessment ofpotential discharges on these water quality standards would be recommended.Another key outcome of the discharge is not the actual impact, but the perceived impact of thedischarge on water quality and estuarine health. If community perceptions were that thedischarge was causing an impact, this may lead to impacts on recreation and tourism values ofthe estuary.• Socio-Economic Values – As outlined for recreation and tourism values. A proportion oftourism to Evans Head will be associated with the use of the estuary for recreational purposes. Ifrecreational opportunities are reduced (either through actual or perceived impacts) then this mayimpact negatively on tourism and economic values associated with the use of the estuary.• Flood Mitigation Values – No impacts identified as a result of any discharge scenariosconsidered.8.7 Discharge Scenario Impact Risk AssessmentThis section provides a review of the impact risk of selected discharge scenarios considered as partof this study. At present, eight discharge scenarios have been considered including:• Ebb-tide release at the Bridge, Revetment Wall and Entrance sites;• Continuous release at the Bridge, Revetment Wall and Entrance sites; and• Wetland / forest releases in the vicinity of the Tuckombil Canal and the confluence of the BrandyArm Creek with the Evans River.Sections 8.1 to 8.6 provide discussion in respect of these discharge scenarios and their potentialimpacts/influences on the following:• Water quality;• Physical constraints impacting on discharge constructability (including factors such as floods,commercial and/or recreational interaction, wave conditions and sand movement);• Potential ecosystem responses; and• Social and environmental value impacts.Construction and operational considerations are also covered in these sections.To determine the ability of the various discharge options (in meeting identified study objectives andavoiding unacceptable outcomes), the potential impacts of discharge scenarios, as well asconstruction and operability factors have been considered against a set of objectives, which relateback to previously identified values. Objectives are outlined further below:• Water quality – Identification of whether the discharge scenario has exceeded ANZECCguideline trigger values for water quality at a given location. For this study, options that havebeen identified to contribute to exceedences of ANZECC guideline trigger values are consideredto present an increased and unacceptable risk of triggering an adverse ecosystem response.Wetland / forest modelling also identified changes to the water balance with the irrigation of STPG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-21effluent onto forested areas resulting increased deep drainage and subsequent groundwaterdischarge. The connectivity between the shallow groundwater and the Evans River is yet to beinvestigated in any detail and as such increasing deep drainage presents a risk of adversegroundwater quality impacts.• Physical considerations affecting design and construction:1. Natural variability in bathymetry – regions with greater variability in bed depths presentgreater potential for discharge infrastructure exposure and burial. The objective is to ensurethat the discharge infrastructure (including pipeline) do not become excessively covered orexposed;2. Increased water velocities – water velocities as a result of tides and floods will increase therisk of damage due to shear stresses on discharge infrastructure. The objective is to ensurethat risks of shear stress failure are minimised;3. Commercial and recreational interaction – a variety of interaction is possible with thedischarge infrastructure as a result of common recreational and commercial related uses ofthe estuary (including snorkelling, SCUBA diving, swimming, fishing, powered and nonpoweredrecreational boating, commercial fishing craft egress and passive recreation. Theobjective is to ensure that these existing uses are not overly compromised;4. Waves and sand movement – wave penetration into the estuary is linked to the extent of theactive entrance marine shoal and within this zone, the sand bed is more dynamic thanelsewhere in the estuary, thereby increasing the risk of sand mobilisation and ingress intothe discharge infrastructure. The objective is to ensure that risks of sand ingress areminimised;5. Construction of the pipeline and discharge infrastructure – the requirements for constructionof the pipeline and discharge infrastructure vary between the options considered. Theobjective here is to minimise potential construction risks.• Operational considerations affecting design and operation:1. Discharge infrastructure fouling with marine growth – marine growth will quickly appear ondischarge infrastructure in the marine environment. The objective is to minimise the risk ofmarine growth causing operational failure (e.g. valves not opening or closing).2. Saltwater corrosion of discharge infrastructure materials – discharge infrastructure (outletand pipeline) may be subject to erosion depending on materials used for construction andhow they are maintained and operated. The objective is to minimise the risk of corrosion.• Potential biological / ecosystem response:1. Increased nutrient concentrations leading to changes in macroinvertebrate abundance anddistribution. The objective here is to minimise risk of disruption to macroinvertebratecommunities;2. Increased nutrient concentrations leading to increased rates of algal growth. The objectivehere is to minimise risk of increased rates of algal growth;3. Flocculation of suspended sediments in STP discharges may lead to nutrient enrichment ofsediments. The objective here is to minimise risk of sediment nutrient enrichment;G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-224. Increased plant growth as a result of increased available nutrient concentrations. Theobjective here is to minimise risk of excessive growth in-stream and littoral floracommunities, particularly weed species.• Social and Environmental Values:1. Nature Conservation Values. The objective here is to minimise impacts to the natureconservation values of the estuary.2. Cultural and Heritage Values. The objective here is to minimise impacts to the cultural andheritage values of the estuary.3. Education and Scientific Values. The objective here is to minimise impacts to the educationand scientific values of the estuary, which primarily relates to the sub-fossil coral reefassemblage.4. Scenic Values. The objective here is to minimise risk to the scenic values of the estuarywhich primarily relates to the discharge of effluent and associated infrastructure.5. Recreation and Tourism Values. The objective here is to minimise impacts on recreationpotential of the estuary, as this may negatively impact on tourism values.6. Socio-Economic Values. The objective here is to minimise economic impacts of thedischarge within the surrounding community.• Factors not considered - Aspects related to pipeline route land acquisition, wetland/forestscheme land acquisition and associated approvals for the pipeline route, and wetland / forestsite, and discharges to the estuary have not been considered in detail as part of this study.Consequently these have not been included in the impact risk assessment.A number of the discharge scenarios to the lower estuary provided similar performance in terms ofwater quality and also provided similar sets of impacts. Based on this, impact risk assessments havebeen limited to consideration of wetland / forest discharges (from both the Tuckombil Canal site andBrandy Arm Creek site) and ebb-tide and continuous releases from the revetment wall.The revetment wall discharge site is favoured over the entrance discharge option as it is likely topresent a more readily constructible option with lower construction risks and potentially costs. Therevetment wall site option provides for similar (albeit slightly lessened) water quality outcomes andprovides the added benefit of having a significant anchor point (i.e. the revetment wall) to secure anydischarge infrastructure, as opposed to what is likely to be a shifting sand bed on the bottom of theestuary for the entrance site. The revetment wall site is favoured over the bridge discharge site as itprovides the improved water quality outcomes due to increased dispersion/tidal exchange at thislocation. The bridge site also has discharge infrastructure closest to the water surface, presenting thegreatest potential opportunity for the general public to interact with it and observe its operation, bothof these factors present inherent risks.Table 8-2 includes a multi-criteria impact risk assessment matrix which identifies key factors asdiscussed in this section. These factors are compared against the objectives established for themand provide a determination of what degree of impact risk the factor presents for the dischargeschemes being compared. It should be noted that not all risks could be quantified as part of thisstudy, hence conservatively where risks are uncertain, these have been identified as a potentialG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-23impact subject to further investigation as identified in the matrix. The colour coding presents an easyvisual tool to assist in interpreting the impact risk outcome.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-24Table 8-2Multi-Criteria Impact Risk Assessment MatrixAspect Region / Value / Element ObjectiveWater Quality(total nutrientconcentrations)Physicalconsiderationsaffectingdesign andconstructionUpper estuaryLower estuaryGroundwaterNatural variability inbathymetryIncreased watervelocitiesCommercial andrecreational interaction• SnorkellingModelled conditionsnot to exceedANZECC guidelinetrigger vales fornutrientsEnsure dischargesfrom the irrigatedforest do notnegatively impactupon groundwaterquality and its usesEnsure that thedischargeinfrastructure(including pipeline)does not becomeexcessively coveredor exposedEnsure that risks ofshear stress failureare minimisedEnsure that theseexisting uses are notoverly compromisedWetland / Forest Discharge(Tuckombil Canal)Guideline trigger values for nutrients alreadyexceeded in upper estuary. The Tuckombil Canalsite discharge is predicted to result in a minorimprovement in TN concentrations in the farupper estuary (i.e. decrease in ambient TNconcentration). The reduction in nutrientsreduces risk of adverse biological effects (e.g.algal bloom) occurring in the upper estuary.Wetland / Forest Discharge(Brandy Arm)Neutral or possibly minor beneficial impact toexisting water quality. ANZECC guidelinetrigger values for nutrients already exceeded inupper estuary.No impact to existing water quality. ANZECC guideline trigger values are achieved in the lowerestuary..Modelling indicated reduced groundwater inflowsfrom the Tuckombil Canal wetland / forest sitewhen compared to the Brandy Arm Creek forest /wetland site. There remains a risk thatgroundwater quality in this zone may be impactedby the scheme and this remains an aspect forfurther detailed investigation.Modelling indicated increased groundwaterinflows from the Brandy Arm Creek forest /wetland site when compared to the TuckombilCanal wetland / forest site. There remains arisk that groundwater quality in this zone maybe impacted by the scheme and this remainsan aspect for further detailed investigation.There may be some active bank erosion and accretion in sections of the upper estuary although themagnitude of this risk is considered to be negligible.No discharge infrastructure to be located within the channel.No impactRevetment Ebb-Tide DischargeRevetment Continuous DischargeGuideline trigger values for nutrients already exceeded in upper estuary and both schemesare predicted to increase nutrient concentrations further. Ebb-tide releases were predictedto result in slightly lower concentrations than the continuous release in the upper estuary.Increasing nutrient concentrations further above the ambient (background) concentrationwhich already exceeds the ANZECC guideline trigger values further increases the risk ofadverse biological responses occurring (e.g. algal bloom).Discharges to the lower estuary provides the best environment for discharge mixing anddilution and the lower estuary has been demonstrated to have low ambient nutrientconcentrations and sufficiently high assimilative capacity to avoid exceedence of theguideline trigger values for nutrients. Further data collection is required to determine ifANZECC guideline trigger values will be exceeded on Airforce Beach, although theassessed incremental increases as a result of the STP discharge are very small.No impactThe entrance shoal which extends from the end of the breakwaters to immediatelydownstream of the Elm Street Bridge is actively shifting as a result of tides and floodmovements, presenting greater risk of scour and sedimentation of discharge infrastructure.Further assessment of the range of estuary bed movement is required to assist indetermining maximum depths at which discharge infrastructure can be placed.The revetment wall site provides a potentially solid foundation to mount the dischargeinfrastructure on to; however, it will still be exposed to high periodic stresses as a result ofhigh water velocities. It is considered that design should be able to limit potential impactsfrom high water velocities.There is some risk of water ingestion during snorkelling activities which may lessen anindividual’s willingness to undertake this activity, however, visibility is unlikely to be affected.• SCUBA diving No impact There is some risk of water ingestion during SCUBA diving which may lessen anindividual’s willingness to undertake this activity, however, visibility is unlikely to be affected.There is an increased risk of physical contact with the release infrastructure which may beencrusted in barnacles presenting an abrasion risk.• Swimming• Fishing• Poweredrecreational boating• Non-poweredrecreation boating• Commercial fishingcraft egress• Passive recreationThe discharge of STP effluent to the estuary may influence an individual’s perceptions of thecleanliness and safety of undertaking swimming within the estuary.Discharges unlikely to affect fish, however, there may be some perceptions of declining fish health orcatch.No impactNo impactNo impactNo impactThe discharge of STP effluent to the estuary may influence an individual’s perceptions ofthe cleanliness and safety of undertaking swimming within the estuary.Fish responses to the discharge have not been determined, although the limited increasesin nutrient concentrations indicate that any response would be minor. There may be someperceptions of declining fish health or catch as a result of the discharge.No impact. There may be some risk of catching an anchor on the discharge infrastructure.No impactBased on current information available for minimum tide levels, bed depths and the drafts ofboats which may use the entrance channel for egress to and from the ocean, the height ofthe discharge infrastructure does not provide sufficient freeboard to eliminate risk of contactand would be unacceptable. The use of appropriate channel markers may lessen this risk toa more acceptable level. Also, further definition of the range of estuary bed depths hasbeen recommended for further investigation to better define the maximum depth at whichthe discharge infrastructure can be located.The discharge of STP effluent may create a visual difference between the discharge andthe ambient water. Density differences between the effluent water and saline estuary waterwill result in effluent rising to the surface leading to the present of surface ripples part of theG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-25Aspect Region / Value / Element ObjectiveOperationalconsiderationsaffectingdesign andoperationSocial andEnvironmentalValuesSand movementConstruction of thepipeline and dischargeinfrastructure(terrestrial)Construction of thepipeline and dischargeinfrastructure (aquatic)Discharge infrastructurefouling with marinegrowthSaltwater corrosion ofdischarge infrastructurematerialsNature conservationvaluesCultural and heritagevaluesEducation and scientificvaluesScenic valuesRecreation and tourismvaluesEnsure that risks ofsand ingress areminimisedMinimise potentialconstruction risksMinimise potentialconstruction risksMinimise the risk ofmarine growthcausing operationalfailureMinimise the risk ofcorrosionMinimise impacts tothe natureconservation valuesof the estuaryMinimise impacts tothe cultural andheritage values ofthe estuaryMinimise impacts tothe education andscientific values ofthe estuaryMinimise risk to thescenic values of theestuaryMinimise impacts onrecreation potentialof the estuaryNo impactWetland / Forest Discharge(Tuckombil Canal)Wetland / Forest Discharge(Brandy Arm)Pipeline route distances to the wetland / forest site are likely to be considerable longer than those tothe lower estuary. Route selection should occur where possible to minimise social and orenvironmental impacts to cultural heritage, noise, air quality, traffic, relocation of existing services,surface and groundwater quality, vegetation, etc.No assessment of geotechnical or soil conditions, for the purposes of pipeline construction, wasmade as part of this study and remains a construction risk.The wetland / forest discharge may take the form of open channels which will not be subject tofouling. If submerged pipes are used, potential for fouling will need to be considered, although theextent of fouling in the upper estuary is unlikely to be as significant as the lower estuary due tochangeable salinity regimes limiting opportunities for marine organism growth.It is likely that concrete infrastructure can be used in the outlet structure for the wetland discharge.Corrosion resistant concrete and reinforcing should be considered for use.The Evans River catchment has a variety of terrestrial flora and fauna values. The siting of thewetland / forest and associated pipelines to this system or to lower estuarine discharge locationswould need to be cognisant of these terrestrial values. It has been assumed that pipeline routes andwetland / forest sites can be selected to mitigate potential risks / impacts in this regard.The pipeline and wetland / forest would need to be sited to avoid significant impact on these values,if any were identified in or adjacent the project footprint.The pipeline and wetland / forest would need to be sited to avoid impacting the subfossil coral reef(in Doonbah locality) as it has been recognised as being of significant scientific value.The wetland / forest system is likely to be sited a significant distance away from highly populatedareas. Furthermore the area will be forested and may not be distinguishable from surroundingareas.As for fishing and swimming above, there may be some perceptions of declining fish health or catchor unsafe swimming conditions. It is possible that these perceptions could be addressed throughmonitoring and public consultation.Revetment Ebb-Tide DischargeRevetment Continuous Dischargetime (most notable for continuous releases). Furthermore, the smell of treated anddisinfected effluent when discharged to the estuary may be noticeable to some persons asthe discharge plumes surfaces. Further investigation of this effect has been recommended.The discharge location is within the activeentrance shoal. The associated movementof sand in this area presents a greater riskof sand ingress into the dischargeinfrastructure, and scour as a result offlooding. Design of ebb-tide releaseoutlets will need to be considered toreduce risk of sand ingress during restperiods. Anchoring to the revetment wallreduces flood scour risks.The discharge location is within the activeentrance shoal. The associated movement ofsand in this area presents a greater risk ofsand ingress into the discharge infrastructure,and scour as a result of flooding. Continuousrelease discharge infrastructure will maintaina positive flow reducing opportunity for sandingress. Anchoring to the revetment wallreduces flood scour risks.Pipeline route distances to the lower estuary discharge sites are likely to be considerableshorter than those to the wetland/forest. Route selection should occur where possible tominimise social and or environmental impacts to cultural heritage, noise, air quality, traffic,relocation of existing services, surface and groundwater quality, vegetation, etc.The revetment wall discharge site was selected to provide an alternative to the Entrancedischarge site which presented significant construction risks. No assessment ofgeotechnical conditions or stability/structural capacity of the breakwaters for the purposes ofpipeline construction were made as part of this study and remain a construction risk.Discharge infrastructure in the lowerestuary will be subject to marine growth.Design of the ebb-tide release outlets willneed to be cognisant of these risks.Similarly maintenance programs will needto account for the potential effects offouling. Failure risks (e.g. valves failing toclose) and associated impacts, such assand or saltwater ingress are increased forebb-tide release infrastructure which hasrest periods.It is likely that the discharge infrastructurewill contain metal components which willbe subject to erosion in saltwater. There isan increased risk of saltwater intrusion upthe discharge pipeline for ebb-tide release.Discharge infrastructure in the lower estuarywill be subject to marine growth.Maintenance programs will need to accountfor the potential effects of fouling (i.e. reducedcapacity to discharge flow).It is likely that the discharge infrastructure willcontain metal components which will besubject to erosion in saltwater. There is areduced risk of saltwater intrusion up thedischarge pipeline for continuous releasesdue to maintenance of positive dischargeflows.Minor increases in nutrient concentrations have been predicted throughout the estuary forebb-tide and continuous release discharge scenarios thereby increasing the risk of abiological or ecosystem response, e.g. changes in macroinvertebrate communityabundance and distribution, increased algal production and associated risk of algal blooms,changes in trophic status of estuary, etc. These outcomes if realised could impact onidentified nature conservation values and have longer term cumulative impacts on theestuary to support certain fish and bird populations. Determination of actual biological /ecosystem response was beyond the scope of this study and would need to be addressedas part of any future detailed assessment of a discharge in this location.As for Nature Conservation Values, impacts to the health of the estuary and its ability tosupport wildlife and harvest seafoods may increase the risk of impacting on cultural valuesassociated with the estuary. Further assessment of biological / ecosystem responsesassociated with the discharge are required.No impactThis discharge increases the risk of discharges being noticeable to the public either throughthe presence of surface ripples, or via differences in water clarity/hue in the immediatevicinity of the discharge. These effects if noticeable would only be noticeable under certainconditions.As for fishing and swimming above, there may be some perceptions of declining fish healthor catch or unsafe swimming conditions. Further assessment of potential impacts ofdischarges on recreational primary and secondary contact, and consumption of cookedaquatic food water quality standards would be recommended, as has a more detailedG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-26Aspect Region / Value / Element ObjectiveSocio-economic valuesFlood mitigation valuesMinimise economicimpacts of thedischarge within thesurroundingcommunityMaintain role ofEvans River estuaryfor mitigation of floodimpacts from theRichmond RiverWetland / Forest Discharge(Tuckombil Canal)Wetland / Forest Discharge(Brandy Arm)Reductions in an individual’s perceived ability to recreate within the estuary may impact on thetourism potential of the estuary, increasing the risk of socio-economic impacts.The potential for the wetland scheme to cause groundwater quality impacts has not been fullyassessed.No impact No impact No impactRevetment Ebb-Tide DischargeRevetment Continuous Dischargedetermination of potential biological/ecosystem responses. It is possible that theseperceptions could be addressed through monitoring and public consultation.Reductions in an individual’s perceived ability to recreate within the estuary may impact onthe tourism potential of the estuary, increasing the risk of socio-economic impacts. Therisks of impact in this respect are increased in the lower estuary as this is where themajority of fishing, swimming and passive recreation, etc is undertaken (immediatelyadjacent to Evans Head). Perceived impacts associated with fishing, swimming, dischargevisibility and potentially smell all increase the risk of socio-economic impact. Furtherassessments are required to better define if actual impacts would be experienced.LegendPotentially significant or unacceptable impact or riskSlight negative impact or riskNeutral impact or riskBeneficial impactG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

DISCHARGE SCENARIO IMPACT RISK ASSESSMENTS 8-278.8 Approval ConsiderationsIt is likely that a variety of approvals and or permits will need to be sought for the construction ofwetland / forest, and or pipeline to the estuary for the purposes of treating / discharging effluent.Some of the key pieces of legislation that may be relevant include:• Environmental Planning and Assessment Act, 1979 – This NSW Act identifies that development(i.e. construction of pipelines, wetland/forest and/or estuarine discharge) may be either:• Permissible with development consent;• Permissible without development consent; or• Prohibited.Development that is permissible with development consent is assessed under the provisions ofPart 4 of the Act. Prohibited development is development that is prohibited and cannot beundertaken. Development that is permissible without development consent is still subject toenvironmental impact assessment, and Part 5 of the Act establishes processes andrequirements. Generally, developments that have the potential for significant environmentalimpact require preparation of Environmental Impact Statement (EIS).• Water Management Act, 2000 – relates to the management of surface and ground water in NSWand for regulation of water and works that affect surface and groundwater, both fresh andmarine.• River and Foreshores Improvement Act, 1948 – DECCW has an approval role under Part 3A ofthe Rivers and Foreshores Improvement Act, 1948 in regard to “Protected Land”. This includesin-channel areas and lands within 40 metres of a river, creek or other water course. Council maybe exempt from the need to obtain a permit under Part 3A but may not be exempt from the intentof the legislation.• Fisheries Management Act, 1994 – Significant floral communities within and adjacent to theestuary, e.g. seagrasses, mangroves and saltmarsh are protected under the FisheriesManagement Act 1994. A permit is required from DPI Fisheries to cut, remove, damage ordestroy marine vegetation in public waterways. The act also provides protection for threatenedfish species.• Crown Lands Act, 1989 - The undertaking of works or the placement of structures within Crownlands requires consent of the appropriate authority this may be the Department of Lands, orDECCW, etc.• The Environment Protection and Biodiversity Conservation Act, 1999. Actions which have asignificant impact on matters of national environmental significance or on the environment ofCommonwealth land may be subject to assessment under the EPBC Act. Triggers forassessment may include impact on World Heritage properties, Ramsar wetlands, nationallythreatened species and ecological communities, migratory species and Commonwealth marineareas.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CONCLUSIONS AND RECOMMENDATIONS 9-19 CONCLUSIONS AND RECOMMENDATIONS9.1 ConclusionsThis report outlines BMT WBM’s investigations into the environmental and social impact risks ofdisposing treated effluent from the Evans Head Sewage Treatment Plant (STP) to the Evans River.The study has been designed to address questions posed by Council, which include identification of:• The ability of the Evans River estuary to accept and assimilate or dissipate STP effluentdischarges; and• The impact of STP discharges on the environmental and social values of the Evans Riversystem.In this respect, the study has assessed a number of STP discharge scenarios, including:• Ebb-tide release scenarios;• Continuous release scenarios; and• Wetland and carbon sequestration forest polishing release scenarios.To enable assessment of the discharges linked hydrodynamic (HD) and advection/dispersion (AD)models were developed. These models were used to assess the relative contributions of keypollutants (nutrients in this instance) at various locations within the estuary. In developing the modelsa variety of field data were collected within the estuary. Both the HD and AD models were calibratedagainst the field datasets and validated against previous available datasets.Potential discharge sites for all options were established in consultation with Council. With the initialdischarge sites identified, release options were developed. This enabled BMT WBM to complete‘near field’ modelling of the discharges using the CORMIX model to provide a first pass assessmentof likely dilution characteristics of the proposed discharges. The results from this ‘near field’modelling were used to inform the ‘far field’ models (i.e. HD and AD models) to allow them to moreaccurately predict plume / pollutant evolution through the estuary.For the wetland / carbon sequestration forest polishing option previously developed models (byothers) were re-established and refined to allow predicted ultimate STP flows to the wetland / forest tobe converted into a time-series of flows and nutrients loads to the estuary. In this form the impacts ofthe wetland / forest release could be assessed using the previously established HD and AD modelssimilarly to the ebb-tide and continuous release options.Subsequent to the scenario runs being completed, the models were interrogated and theconcentrations of key pollutant species (total nitrogen and total phosphorus) contributed by scenariosat points of interest (established in consultation with Council) were extracted from the model. Theadditional concentrations of pollutants as predicted by the models could then be compared toapplicable water quality objectives (WQOs) at that location.The scenario modelling predicted that both the continuous and ebb-tide release options would resultin increases in total nutrient concentrations throughout the estuary (nitrogen more than phosphorus)and at the beach location outside of the estuary. This outcome is a function of tidal movementsG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CONCLUSIONS AND RECOMMENDATIONS 9-2which move treated effluent throughout the estuary. The choice of ebb-tide discharges generallyresults in improved water quality outcomes (i.e. lower TN concentrations) as much of the effluent isconveyed out to the ocean and does not return. However, on certain tides, i.e. neap tides where lowtidal velocities exist, ebb-tide discharges can result in effluent being retained in the estuary orreturned to the estuary from the ocean on the next flooding tide.The movement of effluent throughout the estuary means that circumstances could arise where thedischarge results in modelled concentrations exceeding the guideline trigger values. This is to saythat prior to the discharge, a site may have had ambient water quality conditions below the guidelinetrigger value; however, with the introduction of the effluent, the pollutant concentrations increase andthen exceed the guideline trigger value. This was not noted to occur at any site within the estuary forthe assessments completed as part of this study, although the assessments were focused on oneyear, i.e. 2008.The modelling showed that the magnitude of the increase in total nutrient concentrations variedthroughout the estuary in response to ebb-tide and continuous discharges. All ebb-tide andcontinuous release options were to the lower estuary, correspondingly the greatest modelledincreases in nutrients occurred in this location. However, better (i.e. lower) ambient nutrientconcentrations and increased tidal exchange in the lower estuary mitigates the impacts of thedischarge. The estuary in this zone is able to assimilate nutrients without exceeding the guidelinetrigger values.Modelling indicates that ebb-tide and continuous releases in the lower estuary results in increasednutrient concentrations in the upper estuary. The magnitude of the increase is less than thatobserved in the lower estuary as less effluent gets conveyed to the upper estuary by tidal exchange.Using the ANZECC guideline trigger values as the benchmark for scheme acceptability, thencontinuous and ebb-tide release options to the lower estuary may present an unacceptable risk toestuarine water quality by increasing the risk of an adverse biological response, e.g. algal blooms.However, given that the magnitude of the increases in total nutrients is small (i.e. is typically less than5% above background ambient levels in the upper estuary), further water quality and ecologicalassessments could be employed to quantify these risks should these options be further considered.Outside of the estuary, modelled data were extracted from a beach location. Incremental increasesof up to 0.014 mg/L TN and 0.001 mg/L TP were determined for this location. Due to the limitation ofnot having sufficient background water quality data for the beach location, it has not been possible todetermine the total modelled concentrations of TN or TP at this location sufficient to allow comparisonto ANZECC guideline trigger values.The findings of the assessment completed for the wetland / forest discharge scenarios identified thatthe implementation of the wetland / forest leads to increased in evapo-transpiration (ET) rates (i.e. therate at which water is taken up by evaporation and transpiration). This occurred as a result of theforest having a constant water supply. This effect increased soil moisture deficits (i.e. amount ofrainfall that could be stored prior to runoff) and consequently reduced the volume and frequency ofrunoff events to the estuary. Reductions in volume of runoff events reduce the load of nutrientsdelivered to the estuary, compared to a similar forested area on the same soil profile.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CONCLUSIONS AND RECOMMENDATIONS 9-3Consequently, modelling indicated that were some potential reductions in ambient TN concentrationsin the far upper estuary as a result of the implementation of the Tuckombil Canal wetland / forestoption for treatment and disposal of STP effluent. Full water quality modelling using calibratedcatchment loads and flows is required to refine estimates of the magnitude of the reductions.Section 8 of the study includes an impact risk assessment which compared the performance ofwetland and revetment wall discharge schemes against a set of objectives derived for existingidentified values and construction and operability factors. In particular, Table 8-2 provides an impactrisk assessment matrix for the wetland and ebb-tide / continuous release option at the revetment wallsite.The outcomes of the impact risk assessment were that the wetland / forest discharge schemes wouldbe likely to present neutral or slightly beneficial water quality outcomes within the upper estuary in thecase of the Brandy Arm Creek site, or potentially beneficial outcomes in the case of the TuckombilCanal site, reducing risks associated with adverse biological responses (which were previously notedfor the ebb-tide and continuous release schemes). However, these schemes presented some risksof slightly negative impacts associated with adverse public perceptions of reduced ability to, orenjoyment in recreational activities such as swimming and fishing as a result of a discharge of treatedand polished STP effluent to the estuary. It may be possible to reduce these potential negative risksthrough further assessment and community consultation to address residual community concerns.There are also some unknown factors associated with the wetland / forest site associated with thepotential connectivity of shallow groundwater beneath the forest site and the Evans River estuary andimpact the impact of irrigation on long-term groundwater elevations. Potential impacts of treated andpolished wetland discharges on groundwater quality have also not been assessed. These factorswould be required to be assessed in a more detailed investigation of an actual wetland / forest site.Whereas the ebb-tide or continuous discharges from the revetment wall presents a larger number ofpotential negative impact risks. Many of these could be eliminated or improved through furtherassessment, engineering and design innovation and community consultation and education. Aspectsidentified as presenting significant or unacceptable impact risks included:• Commercial fishing craft egress - Based on current information available for minimum tidelevels, bed depths and the drafts of boats which may use the entrance channel for egress to andfrom the ocean, the height of the discharge infrastructure does not provide sufficient freeboard toeliminate risk of contact. The use of appropriate channel markers may lessen this risk to a moreacceptable level.There is a degree of uncertainty of the range of estuary bed depths that may be present at thislocation and the maximum depth to which the discharge infrastructure can be lowered to reducecontact risks. This has been recommended for further investigation.• Passive recreation - The discharge of STP effluent may create a visual difference between thedischarge and the ambient water due to differences in water clarity. Density differences betweenthe effluent water and estuary water will result in effluent rising to the surface leading to thepresent of surface ripples part of the time (most notable for continuous releases). Furthermore,the smell of treated and disinfected effluent when discharged to the estuary may be noticeable toan individual as the discharge plumes surfaces.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CONCLUSIONS AND RECOMMENDATIONS 9-4There are uncertainties as to the extent of rippling that may occur (and potentially this may bemitigated through design innovation). There is also uncertainty as to whether the smell of thehighly treated and disinfected effluent will be noticeable as the plume surfaces. Furtherassessment of this potential impact would be required.• Socio-economic values - Reductions in an individual’s perceived ability to recreate within theestuary may impact on the tourism potential of the estuary, increasing the risk of socio-economicimpacts. The risks of impact in this respect are increased in the lower estuary as this is wherethe majority of fishing, swimming and passive recreation, etc is undertaken (i.e. immediatelyadjacent to Evans Head). Perceived impacts associated with fishing, swimming, dischargevisibility and potentially smell all increase the risk of socio-economic impact.9.2 RecommendationsThe STP wetland / forest schemes are recommended as the first priority for further investigation.Overall the receiving water quality modelling and associated impact risk assessments identify that theforest / wetland discharge schemes provide a lower social and environmental risk option than therevetment wall ebb-tide or continuous release, subject to further detailed site investigation of theactual wetland / forest site. Initial assessments completed as part of this study recommend a wetland/ forest in the vicinity of the Tuckombil Canal rather than one in the vicinity of Brandy Arm Creek dueto potentially greater receiving water benefits in the Evans River estuary.The revetment wall discharge is recommended as the second priority for further investigation.Although not assessed as part of this study, if costs (or land availability, etc) prove prohibitive for awetland / forest scheme, then a revetment wall discharge would form a second preference. However,this scheme has been identified to present a number of social and environmental risks which withfurther assessment, design and community consultation have the potential to be eliminated orovercome.The adoption of a continuous release arrangement may reduce some operational risks (e.g. sandingress into the discharge infrastructure), but was found to contribute slightly higher total nutrientconcentrations in the upper estuary; the location most at risk of experiencing an adverse biologicalresponse as a result. Hence, it is difficult with the information presently available to recommend aparticular discharge strategy over another. It is recommended that as part of any future more detailedassessment (see below) that both discharge strategies be assessed. If it is determined that thepotential for a biological response is insignificant then a continuous release would be recommendedover an ebb-tide release for its potential operational benefits. A continuous release scheme may alsoprovide for cost savings by avoiding the need for additional transfer infrastructure from the STP to theestuary.The revetment wall site is favoured over other release sites at the Elm St Bridge and Entrance. TheElm St Bridge site has the shallowest bed structure and as such is likely to present the greatest risksfor human interaction with the discharge infrastructure and plume. The Entrance site is considered topresent the most challenging construction option, with the discharge infrastructure to be laid in thelocation of a mobile sand bed. Furthermore, the discharge infrastructure may provide a significantboat navigation hazard.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CONCLUSIONS AND RECOMMENDATIONS 9-59.3 Further AssessmentsAny scheme adopted by Council would need to go through a further round of detailed conceptdevelopment, assessment and costing. At this stage, the scheme could be compared equitably withother schemes already progressed by Council for management of effluent from the Evans Head STPinto the future.Future assessments (potentially forming part of the approval process) may be required for anyestuarine discharge is detailed below:• Full water quality modelling is required to simulate actual pollutant concentrations, rather thanconservative tracers as was undertaken for this study. The full water quality modelling wouldutilise the HD and AD model information already developed and then add an additional layer ofinformation on key processes (i.e. settling, decay, uptake, etc). This model would also be able tosimulate a range of nutrient species, water clarity, dissolved oxygen, faecal coliforms andchlorophyll-a, etc. In addition to allowing for comparisons of predicted receiving water quality withapplicable water quality objectives (i.e. protection of aquatic ecosystems, primary and secondarycontact recreation, etc), this model could also be used to ascertain potential ecosystem /biological responses associated with the discharge options.Further data collection to support the development and calibration of this model will be required.This will include calibration of flow and load predictions of the WaterCAST catchment model.Additional water quality and sediment quality / benthic flux information may also need to becollected to support the model calibration and validation. In particular better information on algalconcentrations in the estuary will be required, as will as a better definition of the quality ofoverflows from the Richmond River/Rocky Mouth Creek to the Evans River.In respect of the wetland site, the following future assessment would be required:• Further assessment of potential wetland sites would be required to establish their feasibility foruse. At present, key unknowns include the connectivity between shallow groundwater beneaththe forest site and the Evans River; the impact of irrigation on the long-term groundwaterelevation at the sites; and potential groundwater quality impacts of the irrigation of treated andpolished effluent from the wetland to the forest.In respect of the ebb-tide and continuous release, the following future assessments would berequired:• Further assessment of the range of estuary bed movement will be required to determine themaximum depths at which discharge infrastructure could be placed and hence determine theassociated risk of contact with vessels. Further discussion with regulatory authorities such asNSW Maritime will also be essential in determining feasibility and mitigation strategies which maybe appropriate; and• Odour assessments, assessments of plume evolution to the surface and the associated odourrisks this presents need to be assessed to determine if this potential risk would be realised.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REFERENCES 10-110 REFERENCESArgent, R. M, Perraud, J-M, Podger, G.M, Murray, N (2008a) WaterCAST Component ModelReference Manual, eWater CRC, Canberra.Argent, R.M, Brown, A, Cetin, L.T, Davis, G, Farthing, B, Fowler, K, Freebairn, A, Grayson, R,Jordan, P. W, Moodie, K, Murray, N, Perraud, J-M, Podger, G. M, Rahman, J, Waters, D. (2008b)WaterCAST User Guide, eWater CRC, Canberra.Australian Wetlands (2006) West Byron STP Wetlands Water Quality Review, Final ReportNovember 2005 – May 2006. Byron Shire Council.BMT WBM, (2008) Ballina Flood Study UpdateBMT WBM, (2010) Richmond River Flood Mapping StudyBOM (2009). Mean monthly and mean annual evapotranspiration (base climatological data sets).Bureau of Meteorology Australia.Brian J. Myers, Warren J. Bond, Richard G. Benyon, Randall A. Falkiner, Philip J. Polglase,Christopher J. Smith, Valerie O. Snow and Swaminathan Theiveyanathan. (1999) SustainableEffluent-Irrigated Plantations: An Australian Guideline. CSIRO Forestry and Forest Products.Brown Consulting, (2006), Woodburn to Ballina Pacific Highway Upgrade.Chiew, F. and Scanlon, P. (2002). Estimation of Pollutant Concentrations for EMSS Modelling of theSouth-East Queensland Region. Cooperative Research Centre for Catchment Hydrology TechnicalReport No. 02/2.Chiew, F. and Siriwardena, L. (2005), Estimation Of SIMHYD Parameter Values For Application InUngauged Catchments. In Zerger, A. and Argent, R.M. (eds) MODSIM 2005 International Congresson Modelling and Simulation. Modelling and Simulation Society of Australia and New Zealand,December 2005, pp. 2883-2889. http://www.mssanz.org.au/modsim05/papers/chiew_2.pdfConnell Wagner (2008) Final Report Woodburn Evans Head Wastewater Management Scheme:Stage 2 Release Investigation, Report #28268, Prepared for Richmond Valley Council, June 2008.Crites, R. Middlebrooks, E and Reed, S. (2006) Natural Wastewater Treatment Systems. Taylor &Francis Group.Department of Land and Water Conservation NSW (1998) The Constructed Wetlands Manual.Digital Atlas of Australian Soils - http://www.toolkit.net.au/shpa. Accessed February 2010.Digital Landcover Type for the Intensive Use Zone of Australia - http://www.toolkit.net.au/liza.Accessed February 2010.Gardner, T. and Davis, R. (eds.) (1998) MEDLI Version 1.2 Technical Manual. QueenslandDepartment of Natural Resources and Mines: Primary Industries and the CRC for WasteManagement and Pollution Control.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REFERENCES 10-2Geolink, et al (2008) Tuckombil Canal - A report regarding a replacement structure for the Canal.Report prepared for the Richmond River County Council.GHD (2006a) Report for Woodburn Evans Head Wastewater Management Scheme. Salty Lagoonand Ebb-tide Release Investigations – Water Quality (Report 1 of 5), Prepared for Richmond ValleyCouncil, April 2006.GHD (2006b) Report for Woodburn_Evans Head Wastewater Management Scheme: Salty Lagoonand Ebb-tide Release Investigations Options Study Report 3 of 5), Prepared for Richmond ValleyCouncil, April 2006.GHD (2006c) Report for Woodburn Evans Head Wastewater Management Scheme. Stage 1 EffluentRelease investigations, Prepared for Richmond Valley Council, September 2006.Hazelton, P. and Murphy, B. (2007) Interpreting Soil Test Results: What do all the numbers mean?CSIRO Publishing.Hydrosphere (2008) Evans Head STP Effluent Management Peer Review of Reuse and ReleaseOptions, Prepared for Richmond Valley Council.Hydrosphere (2009) Evans River Review of Environmental Values and Water Quality Objectives.Report prepared for Richmond Valley Council.Hydrosphere Consulting (2010) Analysis of Evans Head STP Flows – Interim Report. RichmondValley Council.Masters B., Rohde K., Gurner N., Higham W. and Drewry J. (2008), Sediment, nutrient and herbiciderunoff from cane farming practices in the Mackay Whitsunday region: a field-based rainfall simulationstudy of management practices. Queensland Department of Natural Resources and Water for theMackay Whitsunday Natural Resource Management Group, Australia.McKenzie, N.J., Jacquier, D.W., Ahston, L.J. and Cresswell, H.P. (2000), Estimation of soil propertiesusing the Atlas of Australian Soils, CSIRO Land and Water, Report 11/00.MHL (1997c) Evans Head – Preliminary Coastal Processes Study.MHL (2006) DNR Evans River Tidal Data Collection – November 2005 to May 2006, ManlyHydraulics Laboratory Report #1481, November 2006.MHL (2007) Evans head Numerical Pollutant Dispersion Study, Manly Hydraulics Laboratory Report#1796, Prepared for Connell Wagner, December 2007.Morand, T (2001) Soil Landscapes of the Woodburn 1:100,000 Sheet. NSW Department of Land andWater Conservation.NSW Department of Planning (2007), Comprehensive Coastal Assessment.Patterson Britton, (2001) Lismore Floodplain Management StudyPatterson Britton, (2004) Wardell and Cabbage Tree Island Floodplain Management StudyPatterson Britton & Partners Pty Ltd (1999a), Evans River Estuary Processes Study. Richmond RiverShire Council.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

REFERENCES 10-3Patterson Britton & Partners Pty Ltd (1999b), Shaws Bay, East Ballina – Estuary Management Plan.Volume 1: Estuary Processes Study Report. Ballina Shire Council.Powelson. D. and Gerba. C, (1994) Virus removal from sewage effluents during saturated andunsaturated flow through soil columns in Water Research Vol. 28, No. 10, pp. 2175-2181. ElsevierScience.Reed, S.C., Crites, R.W. and Middlebrooks, E.J. (1995) Natural Systems for Waste Management andTreatment. McGraw Hill, New York.The Water and Carbon Group (2009) Wetland Based Effluent Management System, Evans HeadFeasibility Assessment. Richmond Valley Council.USEPA (2002) On-site Wastewater Treatment Systems Manual EPA/625/R-00/008. USEPA.Wainwright (1997) Numerical Modelling of the Evans River.Watson, D. (2010) NSW Maritime, Pers. Comm.WBM Oceanics, (2001) Casino Floodplain Risk Management StudyWBM (2002), Evans River Estuary Management Study and Plan. Report prepared for the RichmondValley CouncilWBM Oceanics, (2003), Impacts of Road Runoff Study - Phase 2 (Final Report). Prepared by WBMPty Ltd for the Moreton Bay Waterways and Catchments Partnership, November 2003.WBM Oceanics (2005) Tuckombil Canal Flood Affect Assessment. Report prepared for RichmondRiver County CouncilWestern, A. (2005), LIZA: Land cover for the intensive use zone of Australia, CRC for CatchmentHydrology. http://toolkit.ewater.com.au/Tools/DownloadDocumentation.aspx?id=1000156Western A. and McKenzie N. (2006) Soil Hydrological Properties for Australia. CRC for CatchmentHydrology. http://toolkit.ewater.com.au/Tools/SHPA/DownloadDocumentation.aspx?id=1000232Wood, M (2010). Richmond River County Council, Pers. Comm.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

EVANS RIVER REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVES (HYDROSPHERE, 2009) A-1APPENDIX A: EVANS RIVER REVIEW OF ENVIRONMENTAL VALUESAND WATER QUALITY OBJECTIVES (HYDROSPHERE,2009)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

RICHMOND VALLEY COUNCILEvans RiverReview of Environmental Values and Water QualityObjectives10 December 2009Suite 6, 26-54 River StreetPO Box 7059 BALLINA 2478 NSWTelephone: 02 6686 0006Facsimile: 02 6686 0078© Copyright 2009 Hydrosphere Consulting

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVESSYNOPSISThis report presents a review of existing water quality guidelines and water quality data from EvansRiver to identify appropriate water quality targets for protection of environmental values and uses ofthe waterway. It is intended that the results of this review will help to inform the assessment ofenvironmental impacts of any potential discharge of treated effluent from Evans Head STP.DisclaimerThis report has been prepared on behalf of and for the exclusive use of Richmond Valley Council,and is subject to and issued in accordance with the agreement between Richmond Valley Counciland Hydrosphere Consulting. Hydrosphere Consulting accepts no liability or responsibilitywhatsoever for it in respect of any use of or reliance upon this report by any third party.Copying this report without the permission of Richmond Valley Council or Hydrosphere Consultingis not permitted.Cover: Evans River Estuary Aerial view (Source: Department of Environment and Climate Change,NSW (Coastal and Floodplain Programs) 29-May-1999. Downloaded from:http://www.ozcoasts.org.au/search_data/display_image.jsp?pBlobNo=3612)REV DESCRIPTION ORIG HYDROSPHEREAPPROVAL0 ISSUED FOR RVC REVIEW HYDROSPHERECONSULTING1 AMENDED AS PER DECCW INTERIMTRIGGER UPDATE NOV 09HYDROSPHERECONSULTINGDATEM. HOWLAND 20 TH NOV 2009R. CAMPBELL 7 TH DEC 2009\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\waterquality objectives\evans river water quality objectives_rev 1.doc

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVESCONTENTS1. INTRODUCTION 11.1 Aims and Approach 12. EXISITNG WATER QUALITY GUIDELINES 22.1 ANZECC (2000) 22.2 Richmond River Catchment Water Quality and River Flow Objectives (DEC, 1999) 32.3 Draft Chlorophyll / Turbidity Reference Values for NSW Estuaries (DECCW, Oct 2009)83. EVANS RIVER WATER QUALITY DATA 103.1 Sample Sites and Methodology 103.2 Results and Discussion 123.3 Summary of Water Quality Conditions in Evans River 204. CONCLUSIONS AND RECOMMENDATIONS 215. REFERENCES 22APPENDIX 1: Richmond River Water Quality Objectives (DEC, 2006)APPENDIX 2: Draft Chlorophyll / Turbidity Reference Values for NSW Estuaries (DECCW, 2009)APPENDIX 3: Assessment of Evans River Water Quality with regard to trigger values\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river waterquality objectives_rev 1.doc

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVES1. INTRODUCTIONRichmond Valley Council (RVC) is currently investigating options for disposal of treated effluent fromthe Evans Head STP. A range of options under consideration involve discharge of effluent to theEvans River at various discharge locations and effluent flow/quality regimes. To assess theenvironmental impact of any effluent discharge to Evans River, RVC is investigating the potentialimpact resulting from the various discharge scenarios. This report provides a summary of theenvironmental values and key performance indicators to be used in this assessment.1.1 Aims and ApproachThis report aims to identify the water quality performance objectives of the Evans River to enable anassessment of potential STP discharge scenarios to various locations within the river. This includeslocal environmental values to be protected, trigger values and critical receiving environments. A briefreview of existing water quality data for the Evans River is provided for further backgroundinformation.The following water quality performance targets have been reviewed: ANZECC Guidelines for Fresh and Marine Water Quality (2000);Richmond River Water Quality Objectives in conjunction with “Local planning for healthywaterways: using NSW Water Quality Objectives” (DEC, 2006); and Draft Chlorophyll / Turbidity Reference Values for NSW Estuaries (DECCW, Oct 2009).Existing water quality data recorded for the Evans River (post 2002) have been collated andsummarised from:RVC’s Evans River water quality monitoring program (RVC, 2007-2009); and The DECCW’s State-wide MER Program, Evans River sites (DECCW, 2007-2008).A comprehensive discussion of all data collected prior to the Evans River Estuary Management Plan(2002) can be found in the data compilation study (MHL, 1999) and the Evans River Processes Study(PBP, 1999).\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 1

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVES2. EXISITNG WATER QUALITY GUIDELINESWater quality guidelines generally include trigger values for selected parameters to be used as abenchmark for assessing the likelihood of adverse environmental impact. If an assigned triggerconcentration is exceeded, this can be interpreted as indicating potential for increased environmentalrisk and may be used as a trigger for a management response or action. National water qualityguidelines were developed by ANZECC (2000) and contain default water quality triggers for generalecosystem types (see below).2.1 ANZECC (2000)The Australian and New Zealand Environment and Conservation Council (ANZECC, 2000) guidelinesprovide a tool for catchment managers to asses and manage ambient water quality. In the absence oflocally derived water quality objectives, the ANZECC guidelines are the key reference for assessingaquatic ecosystem health. The guidelines provide a suite of techniques for assessing the biological,physical and chemical condition of waterways, including default numerical trigger values for key waterquality indicators for various ecosystem types (Tables 3.3.2 and 3.3.3, Chapter 3). The guidelinesapply to water bodies during normal flows (i.e not during rainfall events, or extreme dry periods) andshould not be used directly to set discharge limits or at the boundary of an individual site (DEC,2006). The ANZECC (2000) default guidelines for lowland rivers (

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVES2.2 Richmond River Catchment Water Quality and River FlowObjectives (DEC, 1999)The Richmond River Catchment Water Quality Objectives (WQO) reflect the community’s agreedenvironmental values and long-term goals for ambient waters within the Richmond River Catchment(DEC, 2006). The objectives were agreed by the NSW Government in 1999 after extensivecommunity consultation. The guidelines can be used to provide a benchmark to assess the potentialimpacts of a development on ambient water quality. The Evans River lies within the estuarine reachesof the Richmond River catchment and is connected to the Richmond River at Woodburn via theTuckombil Canal. A barrage at the upstream end of Tuckombil Canal prevents tidal intrusion from theEvans River upstream of this point, but does allow for overflow from the Richmond River and RockyMouth Creek into the estuary during flood. Figure 1 sets out the water quality and river flow objectivesfor the catchment.Figure 1: Richmond River Catchment water quality objectives and river flow objectives (DEC,2006)The objectives set out the community’s uses and values of the rivers, creeks, estuaries and lakessuch as swimming and boating, healthy aquatic life, etc. and define a range of water quality triggervalues to assess whether the condition of the waterway supports those values and uses. The localenvironmental values and community uses of Evans River were defined in detail by the Evans RiverEstuary Management Plan (WBM, 2002) through a review of previous studies and consultation withcommunity stakeholder groups, government authorities and other organisations. Using the dataprovided in the WBM (2002) water quality objectives and river flow objectives from Figure 1 weresummarised as follows:\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 3

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVES Aquatic Ecosystems Visual amenity Secondary contact recreation Primary contact recreation Aquatic foodsThe river flow objectives for the Evans River are summarised as follows: Maintain wetland and floodplain inundation Manage groundwater for ecosystems Minimise effects of weirs and other structures Maintain or rehabilitate estuarine processes and habitatsA copy of the water quality objectives set out by DEC (2006) for the protection of these values anduses is provided in Appendix 1. The electronic version of the objectives is located athttp://www.environment.nsw.gov.au/ieo/Richmond/report-02.htm.Evans River is highly valued by the community as a site for recreational pursuits such as swimming,boating, fishing, as well as more passive recreation including bird and wildlife watching, bushwalkingand picnicking and the river runs through parts of Bundjalung National Park. Commercial fishingceased in the Evans River in 1988. The health of the river is also a key contributor to the appeal ofEvans Head as a tourist destination and therefore an important factor in maintaining the localeconomy. Figure 2 shows recreational fishers in the lower estuary.Figure 2: Fishing off a sand bar in the lower Evans River\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 4

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVESFigure 3: Boating in the mid-estuary, upstream of Iron GatesFigure 4: Camping on the banks of Evans RiverWater quality of the estuary needs to be consistent with the usage in order to protect public health.The lower estuary (downstream of Iron Gates) is used for a number of primary contact recreationactivities such as swimming, where there is a high probability of water being swallowed (WBM,2002). The remainder of the river, upstream of Iron Gates, is predominantly used for secondarycontact recreation activities such as boating and fishing (where there is a low probability of waterbeing swallowed). Reference should be made to the Richmond River Catchment Water Quality\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 5

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVESObjectives and River Flow Objectives (DEC, 1999) for specific details of recommended water qualityguidelines (Appendix 1).Figure 5 shows the areas of primary and secondary recreation in the Evans River. Guidelines for theprotection of these uses are provided in Appendix 1.\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 6

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVESIronGatesFigure 5: Primary and secondary recreation areas in the Evans River, National Parks and boat launching facilities.\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev 1.doc Page 7

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVES2.3 Draft Chlorophyll / Turbidity Reference Values for NSWEstuaries (DECCW, Oct 2009 )The Department of Environment, Climate Change and Water (DECCW) is currently working onderiving water quality objectives for various types of estuaries in NSW (pers. comm. P. Scanes,2009). As part of the State Monitoring Evaluation and Reporting (MER) Process, the DECCW hasrecently been undertaking work to derive values for estuarine water quality for different types ofestuaries. The program involves the collection of water quality data from a range of estuarine systemsas well as utilising existing data. Estuaries were categorised as either lower, mid or upper estuariesbased on recorded salinity readings. Trigger values are derived through the process recommendedby ANZECC (2000) using the 80 th percentile of reference site values utilising existing data incombination with data collected on a monthly basis from numerous reference systems. Referencesystems were identified by comparing the ratio of modelled Total Nitrogen (TN) under current landuseto a hypothetical value where all landuse was assumed to be native vegetation. If the ratio was lessthan 1.5, the system was categorised as a reference system and the water quality values (80 thpercentile) measured in these systems were set as water quality target values (Scanes et. al , 2009).For further information on methodologies, refer to Appendix 2. Values reported by the DECCW areinterim only and may be subject to change dependant on the results from the remainder of theprogram.The interim trigger values provided by DECCW for the Evans River are shown in Table 2 below.Table 2: Draft Chlorophyll/Turbidity Reference Values for NSW Estuaries provided by theDECCW (November 2009).80 th %ile of referenceEstuary class Turbidity (NTU) Chlorophyll-a (ug/L)River – low (*EC>25 mS/cm) 5.0 2.3River – mid (EC10-25mS/cm) 8.0 2.9River – upper (EC

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVESWhile the DECCW interim trigger values for the Evans River are available in draft format only at thistime, they represent the most suitable water quality guidelines for setting long-term goals for EvansRiver water quality available at this time. For more details of the methodology refer to Appendix 2 -memo provided by the DECCW on the process provided for the purposes of this report.\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 9

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVES3. EVANS RIVER WATER QUALITY DATAThe following section presents data collected during the following studies: Evans River water quality monitoring program (RVC, 2007-2009). THE DECCW’s State-wide MER Program, Evans River sites (DECCW, 2007-2008).The following is a summary of baseline data for the system collected after the Estuary ManagementStudy process was completed in 2002 to characterise existing water quality conditions. For datacollected prior to and during the Estuary Management Study Process refer to MHL (1999) and PBP(1999).Richmond Valley Council initiated the Evans River water quality monitoring program in August 2006,following a recommendation of the Estuary Management Plan (WBM, 2002). The program collecteddata over 29 months, with at least one sample per month, finishing in January 2009. This monitoringrepresents the longest period of continuous data recorded for the river system to date. A summaryreport was prepared by a Southern Cross University student for the first 18 months of the program(Aulsebrook, 2008).As part of the State Monitoring Evaluation and Reporting (MER) Process, the DECCW has recentlybeen conducting water quality sampling and analysis at two sites in the Evans River. The programcollected monthly samples over 6 months from August 2007 to April 2008 at sites in the mid-estuary.3.1 Sample Sites and MethodologySampling sites were selected for the RVC monitoring at five points along the Evans River from theriver mouth to the upstream end of Tuckombil Canal. The DECCW sites were close to the twoupstream sites selected by RVC. Table 3 gives a description of sampling site locations and Figure 6shows the location of sample sites.The RVC program included water samples both monthly and opportunistically during events such ashigh rainfall periods, and fish kills. Samples were analysed by Richmond Water Laboratories.The DECCW state wide MER program in the Northern Rivers involves the collection of monthlysamples within estuaries during spring and summer months (mid-Sep to end of Dec). Most estuariesare sampled on a 3-year rolling basis. Evans River was sampled in 2007-2008, with 6 monthlysamples taken from Aug 2007-April 2008. Water quality parameters assessed by each program isprovided in Table 4.\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 10

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVESTable 3: Evans River water quality monitoring program sample site descriptionProgram Sample regime Site name DescriptionPoint 1Upstream end of Tuckombil Canal, downstream ofconfluence with Rocky mouth CreekRVC EvansRiverMonthly andevent samples(18 months)Point 2Point 3The junction of Brandy Arm Creek and Evans RiverEstuaryDoonbahPoint 4Elm Street BridgePoint 5Approximately 300m upstream from mouth of estuaryDECCWMERMonthlysamples (6months)ENV1ENV2Upstream end of Tuckombil Canal, downstream ofconfluence with Rocky Mouth CreekThe junction of Brandy Arm Creek and Evans RiverEstuaryFigure 6: Evans River water quality monitoring program sample site locations\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 11

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVESTable 4: Water quality parameters assessed by RVC monitoring and the DECCW monitoringWater quality parameters assessedRVC Evans RiverpHTurbidity (NTU)Temperature (oC)Dissolved Oxygen (mg/L)Electrical Conductivity (uS/cm)Faecal Coliforms (cfu/100mL)Biological Oxygen Demand (mg/L)Suspended Solids (mg/L)Total Nitrogen (mg/L)Total Phosphorus (mg/L)Total Aluminium (mg/L)Total Iron (mg/L)DECCW MER (Evans River sites)ColourTurbidity (NTU)Temperature (oC)Dissolved Oxygen (mg/L & %)Electrical Conductivity (uS/cm)Salinity (ppt)Secchi disc depth (m)Chlorophyll a (ug/L)Total Nitrogen (ug/L)Total Dissolved Nitrogen (ug/L)Total Phosphorus (ug/L)Total Dissolved Phosphorus (ug/L)3.2 Results and DiscussionThe following section summarises both RVC’s and the DECCW’s water quality monitoring programswhich occurred concurrently although sampling was conducted on different days. A further analysis ofmonitoring results is provided in Appendix 3 which compares long-term ambient conditions (measuredas the median) to ANZECC guideline values for the Richmond River estuarine reaches and theDECCW Draft Chlorophyll and turbidity reference values. Where relevant, reference is made in thefollowing text to this comparison.RainfallAnnual rainfall in 2007 (1263mm) was close to average (approx. 1238mm) when compared to longtermtrends (BOM, 2009). Rainfall in 2008 (1819mm) was significantly higher than average and therewere a number of significant rainfall events in this year particularly in January and February whichbrought about extensive flooding of the Richmond River (Figure 7).\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 12

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVES180160Daily Rainfall (mm)140120100806040200Sep-06 Nov-06 Feb-07 Apr-07 Jul-07 Oct-07 Dec-07 Mar-08 Jun-08 Aug-08 Nov-08 Jan-09Figure 7: Daily rainfall for Evans Head over monitoring periodpHAnalysis of all sites in the Evans River shows that ambient pH conditions (median values) fall withinthe ANZECC guidelines for aquatic ecosystem health and recreational use in estuaries. There is ageneral increasing trend in pH downstream from approximately pH 7 at Point 1 to pH 8 at Points 4 &5. High pH values in the river are due to the influence of seawater (pH8) throughout the estuary. Thedegree to which seawater influences pH is dictated by the tide cycle and the degree of rainfall in thecatchment. The minimum values shown in Appendix 3 illustrate that the river is subject to periods ofacidic water quality and this is likely to be due to catchment inputs from Brandy Arm Creek and RockyMouth Creek, which has been known to have an average pH of 4.99 and some readings as low as pH2.94 (MHL, 1997 cited in MHL, 1999). Both creeks have been identified as draining from areas of acidsulphate soils. Figure 8 shows that significant decreases in pH occurred at upstream sites (Point 1 &2) on several occasions throughout the monitoring period and there was also one low pH valuerecorded for Point 4 in the lower estuary in early 2009.98ANZECCupper limitpH7ANZECClower limit65Aug-06 Nov-06 Feb-07 May-07 Aug-07 Nov-07 Feb-08 May-08 Aug-08 Nov-08 Feb-09Point 1 Point 2 Point 3 Point 4 Point 5Figure 8: Evans River temporal variations in pH Aug 2006-Jan 2009.TemperatureAverage temperatures were within the range expected for this type of estuary on the NSW far northcoast. Temperatures varied as expected with season with maximums of up to 32 o C in summer tominimum temp of 15.4 o C in winter both recorded at Point 2. The temperature of seawater entering theriver system will also have bearing on the overall temperature, particularly during dry periods.\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 13

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVES3530Temperature (oC)25201510Aug-06 Nov-06 Feb-07 May-07 Sep-07 Dec-07 Mar-08 Jul-08 Oct-08 Jan-09Point 1 Point 2 Point 3 Point 4 Point 5 ENV1 ENV2Figure 9: Evans River temporal variations in temperature Aug 2006-Jan 2009Dissolved OxygenANZECC (2000) guidelines recommend a minimum level of 6mg/L dissolved oxygen (DO) forsustainable fish health. Dissolved Oxygen (DO) levels recorded over the monitoring period were goodand within the range for ecosystem health for the majority of the period under normal flow conditions(median range 6.8 - 8.5 mg/L across all sites). DO level dropped below 6mg/L on a few occasions atPoints 1 & 2 and at all sites on one occasion in April 2007. These short-term lower DO events areunlikely to pose significant risk to aquatic ecosystem health. Of note is the fact that DO readings weresampled in-situ and usually in the middle of the day when photosynthetic activity and oxygenproduction is generally high. Therefore, these readings would not have captured the overnightminimum and therefore do not represent the critical time periods for this parameter.11109DO (mg/L)8765432Aug-06 Nov-06 Feb-07 May-07 Sep-07 Dec-07 Mar-08 Jul-08 Oct-08 Jan-09Fish stressbelow 6mg/LPoint 1 Point 2 Point 3 Point 4 Point 5 ENV1 ENV2Figure 10: Evans River temporal variations in dissolved oxygen Aug 2006-Jan 2009\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 14

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVESConductivityConductivity levels were in line with what is expected in estuarine systems with levels at the level ofseawater close to the mouth (median 53.5mS/cm at Point 5, refer Appendix 3) and decreasingtowards the upper reaches of the estuary where freshwater inputs are at their greatest (median 28.5mS/cm at Point 1, refer Appendix 3). Despite the decrease with distance upstream the medianconductivity result for Point 1 indicates that the estuary is quite saline during normal flow. The estuaryis tidal up to the floodgates installed at the upstream end of Tuckombil Canal (WBM, 2002). Periodicdecreases in conductivity indicate periods of freshwater inflow from the catchment and the upstreamRichmond River during floods. This was pronounced at Points 1, 2 & 3 in September 2006 and inearly 2008 at all sites corresponding to high rainfall periods (refer Figure 11 below).70,00060,000Conductivity (uS/cm)50,00040,00030,00020,00010,000seawater0Aug-06 Nov-06 Feb-07 May-07 Sep-07 Dec-07 Mar-08 Jul-08 Oct-08 Jan-09Point 1 Point 2 Point 3 Point 4 Point 5 ENV1 ENV2Figure 11: Evans River temporal variations in conductivity Aug 2006-Jan 2009Faecal ColiformsThe median faecal coliform values (Appendix 3) indicate that over the monitoring period, the ANZECCguidelines for both primary and secondary contact were achieved over the course of the RVCmonitoring program from 2006-2009 (median concentrations were less than 150 cfu/100mL). Therewere a few occasions where high values were recorded at Points 1 & 2. While this may indicatepotential issues at these sites, the overall guidelines were achieved. In estuarine systems it is usual toalso measure the microbiological indicator E.Coli levels as this bacterium is more likely to survive insaline systems than F.Coli. This was not assessed by the program.\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 15

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVES2,500Feacal Coilforms (cells/100mL)2,0001,5001,000500ANZECC upperlimit secondarycontactANZECC upper0limit primarycontactAug-06 Nov-06 Feb-07 May-07 Aug-07 Nov-07 Feb-08 May-08 Aug-08 Nov-08 Feb-09Point 1 Point 2 Point 3 Point 4 Point 5Figure 12: Evans River temporal variations in Faecal Coliforms Aug 2006-Jan 2009NitrogenLike many of the other water quality indicators assessed by this program, Total Nitrogen (TN)concentrations showed a longitudinal trend with distance from the mouth of the estuary (referAppendix 3). TN concentrations recorded at the upstream sites (Points 1 & 2) exceeded ANZECCtrigger values during normal flow conditions (median 0.6mg/L and 0.34mg/L respectively) whilemedian values for samples taken in the lower estuary (Points 3, 4 & 5) were within guideline values.Maximum values were associated with significant rainfall experienced in early 2008 and it is likely thisresult is influenced by flood waters from the Richmond River spilling through Tuckombil Canal.Total Nitrogen (mg/L)3.02.52.01.51.00.50.0Aug-06 Nov-06 Feb-07 May-07 Sep-07 Dec-07 Mar-08 Jul-08 Oct-08 Jan-09Point 1 Point 2 Point 3 Point 4 Point 5 ENV1 ENV2Figure 13: Evans River temporal variations in Total Nitrogen Aug 2006-Jan 2009ANZECCupper limitDissolved nitrogen was not assessed by the RVC program, and therefore the proportion of N directlyavailable for biotic uptake cannot be assessed. However, the DECCW MER program did monitordissolved nitrogen species, and the relative proportion of TN, dissolved inorganic nitrogen (DIN) anddissolved organic nitrogen (DON) from August 2007 to April 2008 as shown for sites ENV 1and ENV2 in Figure 14 below. The results indicate that the dissolved inorganic fraction of nitrogen, that isavailable for biotic uptake, makes up only a small proportion of the total nitrogen at these sites. Themajority of nitrogen in the water column consists of dissolved organic nitrogen or particulate formsthat are not readily available for plant uptake.\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 16

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVESConcentration (mg/L)ENV11.41.21.00.80.60.40.20.0Sep-07 Oct-07 Dec-07 Feb-08 Mar-08TN DIN DONConcentration (mg/L)ENV21.41.21.00.80.60.40.20.0Sep-07 Oct-07 Dec-07 Feb-08 Mar-08TN DIN DONFigure 14: Relative proportion of TN, dissolved inorganic nitrogen (DIN) and dissolved organicnitrogen (DON) from August 2007 to April 2008 for sites ENV 1 and ENV 2 (Source DECCWMER, 2009).PhosphorusBoth spatial and temporal trends in Total Phosphorus (TP) are similar to those seen for TN.Concentrations increased with distance from the river mouth, and maximum values were associatedwith rainfall events, particularly during floods in early 2008. Median values in samples recorded atPoints 1, 2 & 3 over the monitoring period show that ANZECC trigger values were exceeded in overhalf the samples. Sites 4 & 5 in the lower estuary were equal to the trigger values at normal flowconditions (median 0.03mg/L).Total Phosphorus (mg/L)0.400.350.300.250.200.150.100.050.00Aug-06 Nov-06 Feb-07 May-07 Sep-07 Dec-07 Mar-08 Jul-08 Oct-08 Jan-09Point 1 Point 2 Point 3 Point 4 Point 5 ENV1 ENV2ANZECCupper limitFigure 15: Evans River temporal variations in Total Phosphorus Aug 2006-Jan 2009Dissolved forms of phosphorus were not assessed by the RVC program but were assessed by theDECCW MER program. The relative proportion of TP, filterable reactive phosphorus (FRP) anddissolved organic phosphorus (DOP) from August 2007 to April 2008 is shown for sites ENV 1 andENV 2 in Figure 16 below. The results indicate that like nitrogen, the reactive species of phosphorus(FRP) only makes up a small proportion of the total phosphorus at these sites. The majority ofphosphorus in the water column consists of particulate phosphorus associated with suspendedsediments and DOP, both of which are not readily available for plant uptake.\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 17

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVESENV1ENV20.250.25Concentration (mg/L)0.200.150.100.05Concentration (mg/L)0.200.150.100.050.00Sep-07 Oct-07 Dec-07 Feb-08 Mar-080.00Sep-07 Oct-07 Dec-07 Feb-08 Mar-08TP FRP DOPTP FRP DOPFigure 16: Relative proportion of TP, Filterable reactive phosphorus (FRP) and dissolvedorganic phosphorus (DOP) from August 2007 to April 2008 is shown for sites ENV 1 andENV 2 (Source DECCW MER, 2009).Chlorophyll aChlorophyll was one of the key indicators identified and measured by the DECCW MER program.This parameter was not monitored by the RVC program. A brief analysis of results from the 6 monthsof sampling by the DECCW is provided in Table 5 below. Figure 17 presents the chlorophyll aconcentrations measured at each of the MER sites in the Evans River. Ambient chlorophyllconcentrations (assessed as the median) for this sample period were high in comparison to bothANZECC guideline trigger values for estuaries (4μg/L) and DECCW interim trigger value (2.3μg/L forlow and 2.9 μg /L for mid-estuary). Site ENV1 at the upstream end of Tuckombil Canal indicatedenriched productivity at this site particularly during flooding in early 2008.Table 5: Analysis of Chlorophyll a concentrations at sites ENV 1 and ENV2 sampled fromAugust 2007 to April 2008 (Source DECCW MER, 2009).Mean (μg/L) Median (μg/L) Min (μg/L) Max (μg/L) nENV1 30.6 16.0 7.5 107.9 6ENV2 11.6 10.3 7.0 19.4 6\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 18

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVES100Chlorophyl a (ug/L)806040200ANZECCupper limitAug-07 Oct-07 Dec-07 Jan-08 Mar-08 May-08ENV1ENV2Figure 17: Chlorophyll a concentrations at sites ENV 1 and ENV2 sampled from August 2007 toApril 2008 (Source DECCW MER, 2009).TurbidityTurbidity readings in the upper catchment were high with levels generally above both ANZECCaquatic ecosystem triggers (10 NTU) and Draft DECCW triggers (5 NTU low and mid estuary fornormal flow conditions refer Appendix 3). In contrast, the lower estuary (Sites 4 & 5) remained largelywithin guideline values for normal flows, with trigger values only exceeded during rainfall events(Appendix 3). Figure 18 shows significant temporal variations over the monitoring period andcontinual high turbidity conditions and with maximum levels at Points 1 & 2 and ENV1 & 2corresponding to rainfall events. Some of the ecological effects of high turbidity in the upper reacheswere documented by GHD (2007) with the absence of seagrass in the mid to upper estuary. TheEvans River Estuary Management Study also noted that the upper reaches of the Evans River andRocky Mouth Creek are depauperate in respect of benthic marine life (WBM, 2002).908070Turbidity (NTU)605040302010ANZECCupper limit0Aug-06 Nov-06 Feb-07 May-07 Sep-07 Dec-07 Mar-08 Jul-08 Oct-08 Jan-09Point 1 Point 2 Point 3 Point 4 Point 5 ENV1 ENV2Figure 18: Evans River temporal variations in turbidity Aug 2006-Jan 2009.ANZECClower limit\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 19

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVES3.3 Summary of Water Quality Conditions in Evans RiverThe upstream sections of the Evans River is subject to poor water quality conditions posing significantrisk to aquatic ecosystem health and this has been documented in previous studies (PBP, 1999;WBM, 2002; Aulsebrook, 2008) and has been further supported by recent data presented in thisreport. Indicators measured at Sites 1 & 2 in the upper reaches consistently exceeded ANZECCguidelines for aquatic ecosystem health for Chlorophyll a, turbidity, total N and total P during normalflow conditions (measured as the median values over the monitoring period in Appendix 3). TheDECCW’s Draft Chlorophyll / Turbidity Reference Values for NSW Estuaries were also consistentlyexceeded at the upstream sites. Acid sulphate soils in Brandy Arm and Rocky Mouth Creekcatchments are known to contribute to low pH events associated with rainfall and catchment runoff.Elevated levels of Total Iron and Aluminium are also indicative of existing water quality issues atthese sites (PBP, 1999, WBM 2002, Aulsebrook, 2008). Modification of the system due to dredging,construction of Tuckombil canal, and drainage of adjacent land for agriculture leading to the exposureof pyritic soils and subsequent generation of acid sulphate runoff combined with historical waterwaybarriers have all contributed to water quality degradation (WBM, 2002).In contrast, the lower sections of the estuary (Sites 4 & 5) showed generally good water qualityconditions during normal flows and both ANZECC and the DECCW interim trigger values wereachieved for these sites, although there was no data available for Chlorophyll a at the lower sites.Trigger values for primary and secondary recreation were achieved at all sites within the estuaryduring normal flows. However, high faecal coliform levels indicated that water quality in the estuarywas unsuitable for swimming and boating for short periods during high flow and flood events.\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 20

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVES4. CONCLUSIONS AND RECOMMENDATIONSThe DECCW Draft Chlorophyll / Turbidity Reference Values for NSW Estuaries represent the mostappropriate locally derived water quality guidelines available at this time. The trigger values are setas the 80 th percentile of data from reference systems, and therefore represent conditions in largelyunmodified systems.The DECCW does not advocate the use of nutrient concentrations as indicators of ecosystem healthas it is unlikely to be a reliable indication of ecosystem condition due to the complex nature of internalnutrient cycling known to occur in estuarine systems. Turbidity and Chlorophyll-a are recommendedas the primary indicators of estuarine health and in the absence of longer term site-specific data, theinterim guideline values provided by the DECCW for the Evans River should be employed as longtermtargets for the aquatic ecosystem health of the estuary.The environmental objectives for visual amenity, recreation and aquatic foods should be based on theRichmond River Catchment Water Quality Objectives published by DEC in 2006 (included inAppendix 1) and ANZECC (2000).\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 21

EVANS RIVER: REVIEW OF ENVIRONMENTAL VALUES AND WATER QUALITY OBJECTIVES5. REFERENCESANZECC (2000) Australian and New Zealand water quality guidelines for fresh and marine waters. Apublication by the Australian and New Zealand Environment and Conservation Council (ANZECC)and Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ).Aulsebrook, S (2008). An assessment of Water Quality in the Evans River Estuary, NSW.Unpublished third year undergraduate report, Southern Cross University Lismore.DEC (2006). Local Planning for healthy waterways using NSW Water Quality Objectives. Publishedby Department of Environment and Conservation NSW. File available athttp://edit.dev.environmentalmonitoring.keysoft.com.au/userdata/downloads/s//usingnswwqos06167.pdf , downloaded 14 th Oct 2009.DEC (2006). NSW Water Quality and River Flow Objectives: Richmond River. File available athttp://www.environment.nsw.gov.au/ieo/Richmond/report-02.htm, downloaded at 14 th Oct 2009.DECCW (Draft 2009). DRAFT Chlorophyll / Turbidity Reference Values for NSW Estuaries.Unpublished information provided to RVC for the purposes of the Assessment of EnvironmentalImpact of STP Discharge to Evans River brief.GHD (2006). Report for Woodburn Evans Head Wastewater Management Scheme. Salty Lagoon andEbb Tide Release Investigations: Water Quality Report 1 of 5. Richmond Valley Council.MHL (1999). Evans River Estuary Data Compilation Study. Report prepared for Richmond ValleyCouncil.PBP (1999). Evans River Estuary Processes Study. Report prepared for Richmond Valley Council.Scanes, P., Coade, G. and Dela-Cruz, J. (2009) Monitoring, Evaluation and Reporting SamplingProtocols. Prepared for 18 th NSW Coastal Conference, Ballina November 3-6 th 2009 by DECCW.WBM (2000). Evans River Estuary Dredge Feasibility Study. Report prepared for Richmond ValleyCouncil.WBM (2002). Evans River Estuary Management Study and Plan. Report prepared for RichmondValley Council.\\sbs\synergy\projects\09-006 rvc strategic planning 2009-10\working\evans head sewerage\evans river\water quality objectives\evans river water quality objectives_rev1.docPage 22

Appendix 1:Richmond RiverWater Quality Objectives explainedThis section explains each of the eleven Water Quality Objectives (WQOs) developed forNSW rivers and estuaries, and provides guideline levels to assist water quality planningand management. Guideline levels are not provided for industrial water supplies asrequirements are industry specific.See the WQOs that apply to each part of the Richmond River catchment.Achieving each WQO will mean improving poor water quality or maintaining existinggood water quality.Objectives consist of three parts: environmental values, their indicators and theirguideline levels. For example, if the objective is to protect secondary contact recreation(environmental value), we need to keep the faecal coliform levels in the water (theindicator) below a specified number or guideline level.The objectives comprise community-based environmental values and their associatednational criteria drawn from the ANZECC 2000 Guidelines. They provide the statewidecontext for taking this work forward into catchment action plans, regional strategies andlocal environmental plans.Tailoring Water Quality Objectives to local conditionsLocal water quality varies naturally because of various factors, including the type ofland the waters are draining (e.g. soils, slope), or rainfall and runoff patterns (e.g.ephemeral or permanent streams). Different land use and land management practicesalso affect water quality. Local WQOs must take account of these variations, particularlyfor the environmental value of aquatic ecosystems.The ANZECC 2000 Guidelines move away from setting fixed single number water qualitycriteria, and emphasise water quality criteria that can be determined on a case by casebasis, according to local environmental conditions. This is done through the use of localreference data and risk based decision frameworks — see section 2.2.1.4 Tailoringguidelines for local conditions (ANZECC 2000 Guidelines). The ANZECC 2000 Guidelinesestablish default trigger values that are set conservatively and can be used as abenchmark for assessing water quality. Further refinement of the trigger values may beneeded to take account of local conditions, especially for aquatic ecosystems andparticularly in places, or for issues, requiring priority action. This should be consistentwith the approach advocated by the ANZECC 2000 Guidelines of focusing on the actualissue (or threatening process) that is a risk or potential risk to the environmentalvalue(s). The selection of the indicator and derivation of the trigger value should triggeraction or investigation before the environmental value is compromised. Trigger levelsthat have been locally refined must still protect the environmental value and drive localprotection or improvement of water quality.The key indicators and trigger values used here are examples of some of the indicatorslisted in the ANZECC 2000 Guidelines. Key indicators for each environmental value arelisted below.Downstream impactsPlanning and management decisions need to recognise that activities and decisionsmade upstream affect water quality downstream. Where this involves cumulative

impacts for nutrients and sediments, the best approach may be to develop load targetsfor the catchment (see ANZECC 2000 Guidelines).Water Quality ObjectivesMeeting water quality levels suitable for local ecosystems is generally the basis forprotecting the other environmental values, which are the uses people have for water.Aquatic ecosystemsMaintaining or improving the ecological condition of waterbodies and their riparianzones over the long termWhere the objective appliesThis objective applies to all natural waterways.High level protection of aquatic ecosystems applies to waters in and immediatelyupstream of national parks, nature reserves, state forests, drinking watercatchments and high-conservation-value areas. This reflects their largelyunmodified aquatic ecosystems, value in providing natural sources of high-qualitydrinking water, and high levels of recreational use.Even in areas greatly affected by human use, continuing improvement is neededtowards healthier, more diverse aquatic ecosystems.Water quality in artificial watercourses (e.g. drainage channels) should ideally beadequate to protect native species that may use them, as well as being adequatefor the desired human uses. However, full protection of aquatic ecosystems maynot be achievable in the short-term in some artificial watercourses.Artificial watercourses should meet the objectives (including protection of aquaticecosystems) applying to natural waterways at any point where water from theartificial watercourse flows into a natural waterway.Examples of key indicators and their numerical criteria (default trigger values)The following table includes examples of some of the key water quality indicators andrelated numerical criteria (default trigger values) selected from the ANZECC 2000Guidelines, relevant to assessing and monitoring the health of aquatic ecosystems. Touse and interpret these guidelines, see supporting information below and the ANZECC2000 Guidelines. The booklet "Using the ANZECC Guidelines and Water QualityObjectives in NSW" explains key terminology and concepts used in the guidelines, in thecontext of NSW policy.Aquatic ecosystemsIndicatorNumerical criteria (trigger values)Total phosphorus Upland rivers: 20 µg/L Lowland rivers: 25 µg/L for rivers flowing to the coast; 50 µg/Lfor rivers in the Murray-Darling Basin Lakes & reservoirs: 10 µg/L Estuaries: 30 µg/LTotal nitrogen Upland rivers: 250 µg/L Lowland rivers: 350 µg/L for rivers flowing to the coast; 500µg/L for rivers in the Murray-Darling Basin Lakes & reservoirs: 350 µg/L

Estuaries: 300µg/LChlorophyll-a Upland rivers: not applicable Lowland rivers: 5 µg/L Lakes & reservoirs: 5 µg/L. Estuaries: 4 µg/L.Turbidity Upland rivers: 2–25 NTU (see supporting information) Lowland rivers: 6–50 NTU (see supporting information) Lakes & reservoirs: 1–20 NTU Estuaries: 0.5–10 NTUSalinity(electricalconductivity)Upland rivers: 30–350 µS/cmLowland rivers: 125–2200 µS/cmDissolvedoxygen Upland rivers: 90–110% Lowland rivers: 85–110% Freshwater lakes & reservoirs: 90–110% Estuaries: 80–110%Note: Dissolved oxygen values were derived from daytimemeasurements. Dissolved oxygen concentrations may vary diurnallyand with depth. Monitoring programs should assess this potentialvariability.pH Upland rivers: 6.5–8.0 Lowland rivers: 6.5–8.5 Freshwater lakes & reservoirs: 6.5–8.0 Estuaries: 7.0–8.5Changes of more than 0.5 pH units from the natural seasonalmaximum or minimum should be investigated.See supporting informationTemperature See ANZECC 2000 Guidelines, table 3.3.1.Chemicalcontaminants ortoxicantsBiologicalassessmentindicatorsSee ANZECC 2000 Guidelines, chapter 3.4 and table 3.4.1.This form of assessment directly evaluates whether management goalsfor ecosystem protection are being achieved (e.g. maintenance of acertain level of species diversity, control of nuisance algae below acertain level, protection of key species, etc). Many potential indicatorsexist and these may relate to single species, multiple species or wholecommunities. Recognised protocols using diatoms and algae,macrophytes, macroinvertebrates, and fish populations and/orcommunities may be used in NSW and interstate (e.g. AusRivAS).

Supporting informationThe ANZECC 2000 Guidelines advocate a risk-based approach to water qualityassessment and management. That is, the intensity of assessment of currentwater quality status or impacts on water quality should reflect the risk of impactson the achievement/protection of the Water Quality Objective.Trigger values are the numeric criteria that if exceeded indicate potential forharmful environmental effects to occur. The default trigger values provided inANZECC 2000 Guidelines are essentially conservative and precautionary. If theyare not exceeded, a very low risk of environmental damage can be assumed. Ifthey are exceeded, further investigation is "triggered" for the pollutant concerned.Assessing whether the exceedance means a risk of impact to the Water QualityObjective requires site-specific investigation, using decision trees provided in theGuidelines.For Protection of Aquatic Ecosystems in NSW, the ANZECC 2000 Guidelinesprovide default trigger values for major physico-chemical stressors in Tables 3.3.2and 3.3.3 (pages 3.3-10 & 11) and for Toxicants in Table 3.4.1 (page 3.4-5).Note for turbidity trigger values: In general values in the lower part of the rangewill be found in rivers and streams during low flows and/or in more vegetatedcatchments. Values of less than 5 NTU are found in the upper Richmond, which isgood quality. Values in the higher part of the range will be found in rivers andstreams in high flows and lower in the catchment (particularly inland catchments).For lakes and reservoirs, in general the higher values will be found in waterbodiesthat are shallow or in areas with dispersive soils.Note that pH varies naturally. Whilst 6.5-8.5 is the default trigger range, valuesoutside this range should be investigated to assess whether they reflect naturalvariation. For example, some streams in sandstone areas have natural pH rangesas low as 4.5.The approach to protecting the aquatic ecosystem should consider the wholerange of interacting factors - such as variability of water quality over time,sediment interactions, river flow, local geology, land use, the needs of sensitivehabitats, and people's uses for water.Assessing ecosystem health also requires using a range of indicators andconsidering local modifying factors-such as basalt soils that result in naturallyhigher nutrient levels, or estuary opening patterns that affect water quality.However, information on a full range of indicators may not be available fromregular monitoring.Although modified, many non-pristine environments contain important aquaticecosystems. Well-functioning aquatic ecosystems also benefit people using thesewaters, such as by reducing blue-green algal blooms.Reducing diffuse pollutant loads during rainfall and runoff periods should be a keyfocus for improving water quality. It is also important in managing longer termimpacts, such as sedimentation and polluted sediments.The choice of toxicant indicators for use in each management situation is relatedto known past or current activities. Impacts are detected by measuring water,sediment or biota. Natural sources should also be considered.Protecting aquatic ecosystems requires mimicking natural river flow patterns asclosely as possible (see River Flow Objectives explained).Visual amenityAesthetic qualities of waters

Where the objective appliesThe objective applies to all waters, particularly those used for aquatic recreationand where scenic qualities are important.Examples of key indicators and their numerical criteriaIndicators used to assess and monitor visual amenity are summarised in the table.Visual amenityIndicatorVisual clarityand colourNumerical criteria (trigger values)Natural visual clarity should not be reduced by more than 20%.Natural hue of the water should not be changed by more than 10 pointson the Munsell Scale.The natural reflectance of the water should not be changed by morethan 50%.Surface filmsand debrisNuisanceorganismsOils and petrochemicals should not be noticeable as a visible film on thewater, nor should they be detectable by odour.Waters should be free from floating debris and litter.Macrophytes, phytoplankton scums, filamentous algal mats, blue-greenalgae, sewage fungus and leeches should not be present in unsightlyamounts.Supporting informationVisual amenity will be improved by protecting aquatic ecosystems and improvingstormwater management.Visual amenity also needs to be protected to maintain water quality for primaryand secondary contact recreation.Secondary contact recreationMaintaining or improving water quality for activities such as boating and wading,where there is a low probability of water being swallowedWhere the objective appliesThis objective applies to all waters but may not be achievable for some time insome areas.Secondary contact recreation applies in waterways where communities do notrequire water quality of a level suited to primary contact recreation, or whereprimary contact recreation will be possible only in the future.Examples of key indicators and their numerical criteriaIndicators used to assess and monitor water for secondary contact recreation aresummarised in the table.

Secondary contact recreationIndicatorFaecal coliformsNumerical criteria (trigger values)Median bacterial content in fresh and marine waters of < 1000 faecalcoliforms per 100 mL, with 4 out of 5 samples < 4000/100 mL(minimum of 5 samples taken at regular intervals not exceeding onemonth).Enterococci Median bacterial content in fresh and marine waters of < 230enterococci per 100 mL (maximum number in any one sample: 450-700 organisms/100 mL).Algae & bluegreenalgaeNuisanceorganisms< 15 000 cells/mLUse visual amenity guidelines.Large numbers of midges and aquatic worms are undesirable.ChemicalcontaminantsWaters containing chemicals that are either toxic or irritating to the skinor mucous membranes are unsuitable for recreation.Toxic substances should not exceed values in tables 5.2.3 and 5.2.4 ofthe ANZECC 2000 Guidelines.Visual clarityand colourSurface filmsUse visual amenity guidelines.Use visual amenity guidelines.Primary contact recreationMaintaining or improving water quality for activities such as swimming in whichthere is a high probability of water being swallowedWhere the objective appliesThis objective applies in the immediate future to waters within and immediatelyupstream of recognised recreation sites. For many other waters, this is a longtermobjective.Secondary contact recreation levels should apply in areas where primary contactrecreation, such as swimming, is unlikely to be achieved in the immediate future,owing to pollution.Examples of key indicators and their numerical criteriaIndicators used to assess and monitor water for primary contact recreation aresummarised in the table.

Primary contact recreationIndicatorTurbidityFaecalcoliformsNumerical criteria (trigger values)A 200 mm diameter black disc should be able to be sighted horizontallyfrom a distance of more than 1.6 m (approximately 6 NTU).Beachwatch considers waters are unsuitable for swimming if: the median faecal coliform density exceeds 150 colony formingunits per 100 millilitres (cfu/100mL) for five samples taken atregular intervals not exceeding one month, or the second highest sample contains equal to or greater than 600cfu/100mL (faecal coliforms) for five samples taken at regularintervals not exceeding one month.ANZECC 2000 Guidelines recommend: Median over bathing season of < 150 faecal coliforms per 100mL, with 4 out of 5 samples < 600/100 mL (minimum of 5samples taken at regular intervals not exceeding one month).EnterococciBeachwatch considers waters are unsuitable for swimming if: the median enterococci density exceeds 35 cfu/100mL for fivesamples taken at regular intervals not exceeding one month, or the second highest sample contains equal to or greater than 100cfu/100mL (enterococci) for five samples taken at regularintervals not exceeding one month.ANZECC 2000 Guidelines recommend:Median over bathing season of < 35 enterococci per 100 mL(maximum number in any one sample: 60-100 organisms/100mL).ProtozoansAlgae & bluegreenalgaeNuisanceorganismspHTemperatureChemicalcontaminantsPathogenic free-living protozoans should be absent from bodies of freshwater. (Note, it is not necessary to analyse water for these pathogensunless temperature is greater than 24 degrees Celsius).< 15 000 cells/mLUse visual amenity guidelines.Large numbers of midges and aquatic worms are undesirable.5.0-9.0 (see supporting information)15°-35°C for prolonged exposure.Waters containing chemicals that are either toxic or irritating to the skinor mucus membranes are unsuitable for recreation.Toxic substances should not exceed the concentrations provided intables 5.2.3 and 5.2.4 of the ANZECC 2000 Guidelines 2000.

Primary contact recreationIndicatorVisual clarityand colourSurface filmsNumerical criteria (trigger values)Use visual amenity guidelinesUse visual amenity guidelinesSupporting informationMaintain water quality in all areas where water quality levels for swimming arecurrently achieved.The immediate focus should be on improving swimming water quality atrecognised recreation sites, with an emphasis on meeting targets during thebathing season.Over the longer term, water quality will need to improve to meet swimmingobjectives at more locations.Bacterial water quality tests are used to indicate the possible presence of humanpathogens. DEC considers that the use of faecal coliforms and enterococci asindicators provides a suitable expression of the disease risks presented bycontaminated bathing waters and allows for international comparisons to bemade. It will, however, monitor closely scientific developments in this area.Achieving water quality levels that are safe for swimming will also result in saferwater quality for non-potable uses in homesteads.Note that pH in ambient waterbodies varies naturally across the landscape andwith time. The goal should be to retain the natural range of pH.The National Health and Medical Research Council released new guidelines forrecreational water quality in 2005. However, these have not yet been adopted foruse in NSW. Contact Beachwatch or NSW Health public health units for currentinformation on recommended guidelines.Aquatic foods (cooked)Refers to protecting water quality so that it is suitable for the production of aquaticfoods for human consumption and aquaculture activities.(Note: The ANZECC 2000 Guidelines lists this environmental value as Aquacultureand human consumption of aquatic foods)Where the objective appliesThe objective applies to all waters where aquatic foods are taken for noncommercialand commercial harvesting.Examples of key indicators and their numerical criteriaIndicators used to assess and monitor water quality so that it is suitable for theproduction of aquatic foods are summarised in the following table. Other indicators arelisted in the ANZECC 2000 Guidelines and Food Standards Code (ANZFA 1996 andupdates available at www.anzfa.gov.au).

Aquatic foodsIndicatorAlgae & blue-green algaeFaecal coliformsToxicants (as applied toaquaculture activities)Numerical criteria (trigger values)No guideline is directly applicable, but toxins present in bluegreenalgae may accumulate in other aquatic organisms.Guideline in water for shellfish: The median faecal coliformconcentration should not exceed 14 MPN/100mL; with no morethan 10% of the samples exceeding 43 MPN/100 mL.Standard in edible tissue: Fish destined for humanconsumption should not exceed a limit of 2.3 MPN E Coli /g offlesh with a standard plate count of 100,000 organisms /g.Metals:Copper: less than 5 µgm/L.Mercury: less than 1 µgm/L.Zinc: less than 5 µgm/L.Organochlorines:Chlordane: less than 0.004 µgm/L (saltwaterproduction)PCBs: less than 2 µgm/L.Physico-chemicalindicators (as applied toaquaculture activities)Suspended solids: less than 40 micrograms per litre(freshwater)Temperature: less than 2 degrees Celsius change overone hour.Supporting informationTo protect the health of human consumers of aquatic foods (whether derived fromaquaculture, commercial, recreational or indigenous fishing) the ANZECC 2000Guidelines are intended to be used in conjunction with the Food Standards Code(ANZFA 1996 and updates available at www.anzfa.gov.au).The indicators are to assist managers to minimize the exposure of humanconsumers of aquatic food species (eg recreational fishermen) to bacteria-bornedisease. In the case of commercial harvesting and cultured species the relevantrequirements of NSW SafeFoods and the NSW Shellfish Projects OperationsManual need to be met. Also NSW Health recommends against the consumption ofraw shellfish harvested on a non-commercial basis. All such shellfish should bethoroughly cooked to kill pathogens and minimize the risk of food poisoning.Cooking, however, cannot remove the risk of algae toxins or chemicalcontaminants.There is a need to identify all aquatic food sources to ensure that appropriatemanagement is in place to protect the human consumer.The condition of the waterway must be suitable for both individual species andtheir habitats and must protect consumers from chemical contaminants that mayaccumulate in the tissues of aquatic foods or from human pathogens. Manywaterways in NSW produce aquatic foods that are suitable for eating aftercooking.

NSW Health should be consulted about issues that have a direct public healthimpact and concerns about the safety of aquatic foods should be brought to theattention of local public health units.The potential for members of the public, including those in Aboriginalcommunities, who gather shellfish for subsistence or non-commercial purposes tobe exposed to pathogens by eating raw shellfish needs to be considered.The potential presence of microbial pathogens (faecal bacteria, viruses,Cryptosporidium), algal and biotoxins and chemical contaminants needs to beconsidered when assessing the risks associated with shellfish consumption. Inaddition, an understanding of the catchment and actual and potential pollutionsources that may impact on the water quality is essential.Water quality tests for faecal coliform bacteria are used as an indicator of thepossible presence of human pathogens. Improved tests are being developed.Industrial water suppliesThe high economic value of water taken from rivers and lakes for use by industry needsrecognition in water quality planning and management. It has been identified as animportant environmental value through community consultation.As industry water supply needs are diverse, relevant water quality criteria are notsummarised here and the ANZECC 2000 Guidelines do not provide guidance on thewater quality needed for various industries. Sources of water used for industryinvariably have other environmental values, which mostly need water of a higher qualitythan that needed by industry. Further, individual industries generally have the capacityto monitor and treat the available water resources to meet their own needs.This page was published 1 May 2006© Department of Environment and Climate ChangeFEEDBACK

Appendix 2:Draft Chlorophyll / Turbidity Trigger Values for NSW EstuariesNovember 2009IntroductionManagement of estuaries often requires the assessment of current condition againstsome reference condition, to determine if the estuary is degraded or if health variablesare outside an acceptable range. The process described below is an edited andexpanded excerpt from the current draft NSW Monitoring Evaluation and ReportingStrategy estuary monitoring Technical Report (Roper et al. 2009). It describes theprocess that was implemented to develop more specific trigger values for chlorophylland turbidity for NSW estuaries. At the moment, the number of reference systems forwhich data are available is limited, meaning that the triggers are still state-wide withineach estuary class. As further data become available through the MER sampling, it isanticipated that triggers may be able to be developed for regions within the state.MethodThe first step was to divide estuaries in types (or classes) and develop triggersrelevant to each class. The classes are lakes (typically large ICOLLS or coastallagoons) lagoons (smaller ICOLLs and coastal creeks) and rivers (typically largeropen linear estuaries with strong tidal influence). In rivers, triggers have beendeveloped for 3 salinity-defined zones,

each estuary revealed that the data distributions for reference systems in eachestuary class fell in about the same range, minimising any bias.ResultsThis approach identified 6 to 7 reference systems in each estuary class (Table 1) forwhich data were available at the time of writing (November 09). The number ofchlorophyll a samples for each of the lake, river and lagoon class reference estuariesvaried between 15-82, 6-111 and 5-283 per estuary respectively.Table 1 Reference estuaries used for calculation of trigger values for NSWestuaries.Rivers Lagoons LakesBellinger River Baragoot Lake Coila LakeClyde River Lake Brou Conjola LakeMoruya River Cuttagee Lake Durras LakePambula River Merrica River Myall River/LakeSandon River Tabourie Lake St Georges BasinTowamba River Wattamolla Creek Wallagoot LakeTuross RiverWapengo LagoonThe recommended trigger values are shown below in Table 2. Please note thattrigger values will continue to be updated as more data become available through theMER sampling of northern region estuaries in 09/10 and other processes. To dateMER sampling has been conducted in the central (07/08) and southern (08/09)regions. Following 09/10 sampling, triggers are likely to be recalculated on a threeyear cycle corresponding with completion of subsequent rounds of resampling in thesouthern, central and northern regions.Table 2 Calculated trigger values for NSW estuaries by type.Chlorophyll (ug/L)Turbidity (NTU)Estuary class 80 th %ile ofreferenceEstuary class 80 th %ile ofreferenceRiver - low 2.3 River - low 5.0River - mid 2.9 River - mid 8.0River - upper 3.4 River - upper 13.7 *Lake 3.6 Lake 5.7Lagoon 2.0 Lagoon 3.3* this value is questionable and will be revised as more data become available.ReferencesANZECC. (2000). Australian and New Zealand guidelines for fresh and marine waterquality. National Water Quality Management Strategy. Paper No. 4. Australian andNew Zealand Environment and Conservation Council. Agriculture and ResourceManagement Council of Australia and New Zealand.Roper, T., Creese, B., Scanes, P., Stephens, K., Dela-Cruz, J. and Coates, B. (2009).Estuaries and coastal lakes draft technical report, NSW State of the Catchments2008. NSW Department of Environment, Climate Change and Water and NSWDepartment of Industry and Investment - Fisheries.

Ryther, J.H. and Dunstan, W.M. (1971). Nitrogen, phosphorus, and eutrophication inthe coastal marine environment. Science, vol. 171 pp. 1008-1112.

Appendix 3:Assessment of Evans River Water Quality with regardto trigger valuesThe following table provides the results of the water quality analysis for each parameter overthe RVC monitoring period and the DECC MER program for Chlorophyll a and Turbidity.Minimum, maximum, median and average values were calculated for each site. Medianvalues were assessed against both ANZECC trigger values for estuaries and the DECCinterim triggers and exceedances are shown in Table 1. Table 1 shows summary data plottedfor each site and ANZECC guidelines for aquatic ecosystem protection are shown as dottedlines.Table 1: Summary of Evans River water quality analysis Aug 2006-Jan 2009pHDissolved Oyygen (mg/L)Point 1 Point 2 Point 3 Point 4 Point 5 Point 1 Point 2 Point 3 Point 4 Point 5Average 7.3 7.4 7.8 8.0 8.1 Average 7.1 6.8 7.6 8.2 8.4Median 7.4 7.5 7.8 8.1 8.1 Median 7.3 6.8 7.7 8.3 8.5Min 5.5 6.4 6.8 5.2 7.0 Min 4.4 4.4 4.6 5.5 5.6Max 8.1 7.9 8.2 8.3 8.4 Max 9.2 9.1 9.1 9.5 9.6n 38 38 38 38 38 n 38 38 38 38 38Electrical Conductivity (u/cm)Faecal Coliforms (cells/100mL)Point 1 Point 2 Point 3 Point 4 Point 5 Point 1 Point 2 Point 3 Point 4 Point 5Average 25758 33361 40416 48852 49301 Average 132 152 35 38 20Median 28500 37700 49050 53450 53450 Median 24 19 14 10 3Min 18 28 38 53 53 Min 1 0 0 0 0Max 46300 51000 53400 54800 57300 Max 2000 2150 230 397 260n 38 38 38 38 38 n 35 33 27 27 19Total Nitrogen (mg/L)Total Phosphorus (mg/L)Point 1 Point 2 Point 3 Point 4 Point 5 Point 1 Point 2 Point 3 Point 4 Point 5Average 0.69 0.46 0.30 0.19 0.14 Average 0.09 0.05 0.04 0.03 0.03Median 0.60 0.34 0.19 0.13 0.12 Median 0.07 0.04 0.04 0.03 0.03Min 0.14 0.03 0.01 0.02 0.01 Min 0.00 0.00 0.00 0.00 0.00Max 2.40 1.50 1.10 0.90 0.52 Max 0.36 0.16 0.14 0.07 0.08n 38 38 38 35 33 n 26 24 23 20 20Chlorophyll a (ug/L)Turbidity (NTU)ENV1 ENV2 ENV1 ENV2 Point 1 Point 2 Point 3 Point 4 Point 5Average 30.59 11.58 Average 22.52 15.285 21.3 14.5 6.3 3.3 3.6Median 15.98 10.29 Median 21.15 12.6 18.0 8.7 2.7 1.4 1.3Min 7.52 6.96 Min 10.70 6.22 3.2 0.4 0.3 0.2 0.2Max 107.92 19.39 Max 37.10 34 83.0 67.7 44.0 46.2 51.1n 6 6 n 6 6 38 38 38 38 38Exceed ANZECCExceed DECCW interim triggers (low and mid estuary)Exceed bothachieve guidelines

pH987654pHPoint 1 Point 2 Point 3 Point 4 Point 5UPSTREAMDOWNSTREAMANZECCupper limitANZECClower limitAverageMedianMinMaxTurbidity (NTU)100806040200TurbidityPoint 1 Point 2 Point 3 Point 4 Point 5UPSTREAMDOWNSTREAMAverageMedianMinMaxANZECCupper limitTempDissolved OxygenTemperature40302010AverageMedianMinMaxDO (mg/L)1098765AverageMedianMinMaxFish stressbelow 6mg/L0Point 1 Point 2 Point 3 Point 4 Point 54Point 1 Point 2 Point 3 Point 4 Point 5UPSTREAMDOWNSTREAMUPSTREAMDOWNSTREAMEC (uS/cm)700006000050000400003000020000100000Electrical ConductivityPoint 1 Point 2 Point 3 Point 4 Point 5UPSTREAMDOWNSTREAMSeawaterAverageMedianMinMaxF.Coli (cells/100mL)2000150010005000Faecal ColiformsPoint 1 Point 2 Point 3 Point 4 Point 5UPSTREAMDOWNSTREAMAverageMedianMinMaxANZECC upperlimit secondarycontactANZECC upperlimit primarycontactTotal NitrogenTotal Phosphorus2.50.40TN (mg/L)2.01.51.00.50.0Point 1 Point 2 Point 3 Point 4 Point 5AverageMedianMinMaxANZECC upperlimit AquaticecosystemsTP (mg/L)0.300.200.100.00Point 1 Point 2 Point 3 Point 4 Point 5AverageMedianMinMaxANZECC upperlimit AquaticecosystemsUPSTREAMDOWNSTREAMUPSTREAMDOWNSTREAMFigure 1: Evans River water quality analysis for the monitoring period Aug 2006- Jan2009

ANALYSIS OF EVANS HEAD STP FLOWS INTERIM REPORT (HYDROSPHERE, 2010) B-1APPENDIX B: ANALYSIS OF EVANS HEAD STP FLOWS INTERIMREPORT (HYDROSPHERE, 2010)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

Richmond Valley CouncilAnalysis of Evans Head STP FlowsInterim Report09-006May 2010Suite 6, 26-54 River StreetPO Box 7059 BALLINA 2478 NSWTelephone: 02 6686 0006Facsimile: 02 6686 0078© Copyright 2010 Hydrosphere Consulting

EVANS HEAD STP FLOW ANALYSISDisclaimerThis report has been prepared on behalf of and for the exclusive use of Richmond Valley Council,and is subject to and issued in accordance with the agreement between Richmond Valley Counciland Hydrosphere Consulting. Hydrosphere Consulting accepts no liability or responsibilitywhatsoever for it in respect of any use of or reliance upon this report by any third party.Copying this report without the permission of Richmond Valley Council or Hydrosphere Consultingis not permitted.PROJECT 09-006 – EVANS HEAD STP FLOW ANALYSIS – INTERIM REPORTREV DESCRIPTION AUTHOR REVIEW APPROVAL DATE0 Draft issued for RVC review R Campbell M. Howland M. Howland 28/4/101 Incorporating RVC comments R Campbell M. Howland M. Howland 3/5/10Evans STP Flow Analysis Interim Report Rev 1.doc

EVANS HEAD STP FLOW ANALYSISCONTENTS1. INTRODUCTION .....................................................................................................................11.1 Terms of Reference....................................................................................................................11.2 Methodology...............................................................................................................................11.3 Data............................................................................................................................................22. PART 1: ANALYSIS OF STP INFLOW....................................................................................42.1 Instantaneous Flow ....................................................................................................................42.2 Groundwater Influences .............................................................................................................62.3 Dry Periods.................................................................................................................................62.4 Holiday Periods ..........................................................................................................................72.5 Tides...........................................................................................................................................92.6 Summary of Part 1 ...................................................................................................................102.7 Current STP Flows ...................................................................................................................113. PART 2 – PREDICTION OF FUTURE INFLOWS.................................................................143.1 Future Dry Weather Flows .......................................................................................................143.1.1 Wastewater Generation...................................................................................................143.1.2 Dry Weather Groundwater Infiltration..............................................................................153.1.3 Current and Future Dry Weather Flows ..........................................................................163.2 Future Wet Weather Flows ......................................................................................................173.3 Future STP Inflow.....................................................................................................................174. PART 3 – ANALYSIS OF STP INFLOW AND OUTFLOW....................................................195. PART 4 – FUTURE EFFLUENT FLOW SCENARIOS ..........................................................215.1 Continuous Discharge..............................................................................................................215.2 Potential Transfer System Options ..........................................................................................215.3 Ebb-Tide Discharge .................................................................................................................215.4 Scenario Analysis.....................................................................................................................215.5 Results .....................................................................................................................................225.6 Summary of Part 4 ...................................................................................................................24REFERENCES......................................................................................................................................26Evans STP Flow Analysis Interim Report Rev 1.docPage iii

EVANS HEAD STP FLOW ANALYSISTABLESTable 1: Sewerage System and STP Design Flow Data ......................................................................11Table 2: Historical STP Inflow Data ......................................................................................................11Table 3: Future EP Loads (GHD, 2008b)..............................................................................................14Table 4: Future Wastewater Flows .......................................................................................................15Table 5: Future Dry Weather Groundwater Infiltration ..........................................................................15Table 6: Dry Weather Flow Components ..............................................................................................16Table 7: Total Volume (over 861 days) and Average Daily STP Flows................................................20Table 8: Future Flow Scenarios ............................................................................................................23FIGURESFigure 1: Inflow, rainfall and groundwater data.......................................................................................5Figure 2: Wet period data........................................................................................................................6Figure 3: Dry period data ........................................................................................................................7Figure 4: Wet holiday period ...................................................................................................................8Figure 5: Drier holiday period..................................................................................................................8Figure 6: Tide and groundwater data ......................................................................................................9Figure 7: Daily peak tide and STP inflow data ......................................................................................10Figure 8: Components of Current STP inflow .......................................................................................13Figure 9: Current and future dry weather flow ......................................................................................16Figure 10: Current and future (showing a 40% reduction) wet weather flow (excluding wastewatergenerated by the population) ................................................................................................................17Figure 11: Total future STP inflow.........................................................................................................18Figure 12: STP inflow and outflow ........................................................................................................19Figure 13: Daily inflow and outflow .......................................................................................................20Figure 14: Effluent Transfer to Evans River ..........................................................................................22Figure 15: Effluent Transfer to Evans River – Scenario Results ..........................................................23Figure 16: Overflow to Salty Lagoon – Scenario Results .....................................................................24Figure 17: Effluent Transfer to Evans River – Base Scenarios 1 (Continuous) and 3 (Ebb-tide).........25Evans STP Flow Analysis Interim Report Rev 1.docPage iv

EVANS HEAD STP FLOW ANALYSIS1. INTRODUCTION1.1 Terms of ReferenceRichmond Valley Council (RVC) is currently investigating options for discharge of treated effluent fromEvans Head STP. Council has commissioned BMT WBM to assess the environmental impact of STPdischarges to the Evans River at various locations and under various discharge constraints. Toenable modelling and assessment of the flow scenarios, BMT WBM requires data on flows to bedischarged from the STP in the future. Hydrosphere Consulting has been commissioned to analysethe main factors affecting STP flows and determine the likely future flows from the STP.1.2 MethodologyThe main objective of this report is to provide information on effluent discharge scenarios to BMTWBM to enable environmental assessment of the discharge options to the Evans River. This willfocus on the ultimate (2050) discharge scenario (taking into account future population growth andinflow and infiltration reduction) as well as the environmental constraints identified by BMT WBM. Theflow scenarios being considered by BMT WBM are:Continuous discharge at 4 sites extending from the entrance to the upper reaches of theEvans River estuary;Ebb-tide release at the 4 sites; andWet weather release from a wetland and carbon sequestration forest (at 4 potentiallocations).Ideally, the transfer system options would be defined on the basis of achievable on-site storageoptions that would provide a buffer for the large discharge events as well as optimisation of thestorage/transfer system design. Given the focus of BMT WBM’s current engagement is a feasibilityassessment only, and also considering the time constraints for provision of this data, a theoreticalapproach to the transfer system options has been adopted. At this stage, RVC needs to narrow downthe many discharge scenarios into feasible scenarios i.e. options that are acceptable in terms ofenvironmental impact on the Evans River. If at a later stage a particular scenario is considered to befeasible and warrants further development, options for optimising the transfer system incorporatingspecific engineering advice, will be undertaken at that time. Similarly, the impact of STP overflowevents to Salty Lagoon (i.e. flows that exceed the discharge system capacity) will not be consideredas a limiting factor at this stage. However, how often and how much effluent is likely to be dischargedto Salty Lagoon under each scenario will be defined.For BMT WBM’s modelling tasks, the required data are a time series of STP effluent flows for thescenario modelling period (between the commissioning date of the new STP and the present) for thevarious discharge scenarios.The following tasks have been undertaken:Part 1: Analysis of STP inflows, holiday loads, rainfall, tides, groundwater level to establishrelationships (if any) between these parameters and the STP inflow.Evans STP Flow Analysis Interim Report Rev 1.doc Page 1

EVANS HEAD STP FLOW ANALYSISPart 2: Prediction of future inflows. In future, only 2 key parameters – inflow/infiltration andpopulation – are assumed to change. At this stage, climatic factors are assumed to reflecthistorical patterns and match the climatic sequence utilised by BMT WBM in thehydrodynamic and water quality modelling. For this reason analysis of wastewater generatedby the future population and the influence of rainfall was undertaken separately. The current(2010) and future (2050) flows are presented as sequences overlaying the historicalhydrological time period (2007-2010) being analysed by BMT WBM. In this way, themodelling can demonstrate the impact of STP discharges under known climatic andhydrodynamic conditions.Part 3: Analysis of STP inflows and effluent flows to determine the relationship between inflowand outflow.Part 4: Production of a time-series of predicted future effluent flows (at ultimate developmentconditions = 2050) under continuous and ebb-tide flow conditions.Part 5: Modification of the discharge scenarios to achieve the constraints identified by BMTWBM.This interim report addresses the first four parts with Part 5 to be undertaken iteratively with BMTWBM.1.3 DataThe following data have been used for this project:RVC has provided flow data from the STP:o Inflow measured at the inlet works flow meter. This flow meter records the flowsentering the plant plus the flows pumped from the supernatant pump station and thedrainage pump station. Data since October 2007 have been used as they areassumed to be representative of the flows into the new STP.o Maximum instantaneous flow recorded at the flow meter.o Outflow measured at the EPA licence monitoring point.Rainfall data has been sourced from the Bureau of Meteorology for the Evans Head RAAFBombing Range AWS (station 058212) and the SILO database.Tide levels have been sourced from the MHL Richmond River station (Evans Head);Groundwater levels have been sourced from the Salty Lagoon Ecosystem MonitoringProgram for BH16 (Flame Street, Evans Head) and BH17 (Terrace Street, Evans Head);Data on STP and sewerage system capacity have been taken from:o NSW Department of Commerce (2005) Detailed Concept Development for the EvansHead Sewage Treatment Plant Augmentationo GHD (2008a) Richmond Valley Council, Report on Review of Woodburn SewerageAugmentation StrategyEvans STP Flow Analysis Interim Report Rev 1.doc Page 2

EVANS HEAD STP FLOW ANALYSISo GHD (2008b) Richmond Valley Council, Report on Review of Evans Head SewerageAugmentation Strategyo GeoLINK (2009) Evans Head & Woodburn Water Recycling Scheme, Assessment ofScheme Optionso GHD (2007) Broadwater Sewerage Scheme Detailed Design - Design OptionsReport.Evans STP Flow Analysis Interim Report Rev 1.doc Page 3

EVANS HEAD STP FLOW ANALYSIS2. PART 1: ANALYSIS OF STP INFLOWThe sewerage flows into the STP consist of:1. Wastewater generated by the population (permanent and/or holiday periods);2. Groundwater infiltration during dry weather; and3. Additional sewerage flows during wet weather.The total of the above three components is the STP inflow (flow measured at the inlet work less thesupernatant and drainage pump station flows).Figure 1 shows the inflow to the STP between 16/10/07 and 22/2/10, maximum instantaneous inflowrecorded at the inlet works, AWS rainfall and groundwater level at BH16 (for the period of record).A statistical correlation between rainfall and STP inflow (total and wet weather flows) has beenexplored but a direct relationship is not apparent, and was not expected, due to the multi-dimensionalnature of the relationship between rainfall, groundwater level, wastewater generation and STP inflow.The alternative approach of analysing the quantifiable components contributing to effluent flow andthen applying appropriate corrections to the residual has been undertaken for this report.2.1 Instantaneous FlowThe Evans Head pump stations transfer flow to the Evans Head STP from Evans Head andWoodburn. The combined peak flow from the existing pump stations and the drainage andsupernatant pump stations is approximately 100 L/s. Theoretically, any flow greater than 100 L/s cannot be recorded at the STP. From Figure 1, there are many occasions where the maximuminstantaneous flow exceeds 100 L/s (up to 135 L/s). This is due to flow build-up behind the stepscreen caused by rags, etc. As the screen steps up, this flow is released, increasing the measuredpeak flow. These higher peak flows are therefore not representative of the pumped flows to the STP.From Figure 1, it can be seen that the high maximum instantaneous flows do not correspond with thehigh daily flows and vice versa, low maximum instantaneous flows do not correspond with the lowdaily flows. Therefore, the high maximum instantaneous flows do not assist with the analysis of dailyflow into the STP.Evans STP Flow Analysis Interim Report Rev 1.doc Page 4

EVANS HEAD STP FLOW ANALYSIS1806000Rainfall (mm)16014012010080604020016/10/200715/11/200715/12/200714/01/200813/02/2008Figure 1: Inflow, rainfall and groundwater data14/03/200813/04/200813/05/200812/06/200812/07/200811/08/200810/09/200810/10/20089/11/20089/12/20088/01/20097/02/20099/03/20098/04/20098/05/20097/06/20097/07/20096/08/20095/09/20095/10/20094/11/20094/12/20093/01/20102/02/2010AWS Rainfall (mm) Holiday Periods Maximum Inflow x 10 (L/s) Sewage Inflow to STP - current (kL/d) Groundwater level (mmAHD)Evans STP Flow Analysis Interim Report Rev 1.doc Page 5500040003000200010000Inflow (kL/d) and Max Instantaneous Flow x10 (L/s) and GroundwaterTable (mmAHD)

EVANS HEAD STP FLOW ANALYSIS2.2 Groundwater InfluencesThe Evans Head sewerage system is known to be subject to significant amounts of infiltration andinflow during wet weather.Figure 1 shows that high sewage inflows correspond with high rainfall and high groundwater level.Data for a period of wet weather and high groundwater table (20/3/09 to 11/7/09) are shown in Figure2. Rainfall during this period totalled 1,127 mm (average of 10 mm per day) with a maximum of 133mm. It can be seen that high rainfall days cause an increase in groundwater level and the STP inflow.In addition, sustained periods of rainfall (such as in April 2009) and high rainfall days raise thegroundwater level and increase the STP flow for long periods of time (1-4 weeks depending on thefrequency, duration and magnitude of the rain events). The short-term sequence is a combination ofdirect rainfall effects as well as groundwater infiltration, whilst the longer term response mirrors thegroundwater level variation.1806000Rainfall (mm)1601401201008060402050004000300020001000Inflow (kL/d) and Groundwater Table (mmAHD)0020/03/0927/03/093/04/0910/04/0917/04/0924/04/091/05/098/05/0915/05/0922/05/0929/05/095/06/0912/06/0919/06/0926/06/093/07/0910/07/0917/07/0924/07/09AWS Rainfall (mm) Sewage Inflow to STP - current (kL/d) Groundwater level (mmAHD)Figure 2: Wet period data2.3 Dry PeriodsFigure 3 shows data for a period of low groundwater table and low rainfall (1/9/09 to 26/10/09).Rainfall during this period totalled 98 mm (average of 1.8 mm per day) with a maximum of 19 mm.This period is not a holiday period. From this figure, it can be seen that the groundwater table dropswith the reduced rainfall and the STP inflow remains relatively constant. The average inflow duringthis period was 1,063 kL/d. This figure is regarded as the best estimate of the effluent generation bythe permanent population with minimal other influences.Evans STP Flow Analysis Interim Report Rev 1.doc Page 6

EVANS HEAD STP FLOW ANALYSIS1804500Rainfall (mm)16014012010080604020Dry period average STP inflow = 1.063 ML/d4000350030002500200015001000500Inflow (kL/d) and Groundwater Table (mmAHD)0015/08/200922/08/200929/08/20095/09/200912/09/200919/09/200926/09/20093/10/200910/10/200917/10/200924/10/200931/10/2009AWS Rainfall (mm)Groundwater level (mmAHD)Sewage Inflow to STP - current (kL/d)Dry Period Average InflowFigure 3: Dry period data2.4 Holiday PeriodsDuring holiday periods, the current STP inflow would be expected to increase with increased visitorsto Evans Head and Woodburn. The following figures show holiday periods corresponding with wetweather (December 2007/Jan 2008, total rainfall 260mm) and drier weather (December 2009/Jan2010, total rainfall 168mm). The average STP inflow for each case was:December 2007/Jan 2008 – 1,840 kL/dDecember 2009/Jan 2010 – 1,301 kL/dIn both cases, the STP inflow increases above the dry period flows, but the effect of wet weather ismore significant than the effect of the increased holiday population. Groundwater data are notavailable for these periods.Evans STP Flow Analysis Interim Report Rev 1.doc Page 7

EVANS HEAD STP FLOW ANALYSIS1803500Rainfall (mm)1601401201008060402030002500200015001000500Inflow (kL/d)0016/10/200715/11/200715/12/200714/01/200813/02/200814/03/2008AWS Rainfall (mm) Holiday Periods Sewage Inflow to STP - current (kL/d)Figure 4: Wet holiday period180180016016001401400Rainfall (mm)120100806012001000800600Inflow (kL/d)4040020200001/12/200931/12/200930/01/2010AWS Rainfall (mm) Holiday Periods Sewage Inflow to STP - current (kL/d)Figure 5: Drier holiday periodEvans STP Flow Analysis Interim Report Rev 1.doc Page 8

EVANS HEAD STP FLOW ANALYSIS2.5 TidesSea level changes may influence the groundwater level through either sea water infiltration or tidalpumping of fresh groundwater. Data on groundwater level in Evans Head (BH16) and closer to thecoast (BH17) are shown in Figure 6, with the tide data for the mouth of the Evans River. There doesnot appear to be any influence of tides on the groundwater table.463.553Tide (m)2.521.510.54321Groundwater Level (m AHD)020/05/09 9/07/09 28/08/09 17/10/09 6/12/090BH17 (mAHD) Tide (m) BH16 (mAHD)Figure 6: Tide and groundwater dataDaily peak tides and STP inflows for the period of low groundwater table (August – October 2009) areshown in Figure 7. It is concluded that tides have no significant influence on STP inflows and can bediscounted in future analyses.Evans STP Flow Analysis Interim Report Rev 1.doc Page 9

EVANS HEAD STP FLOW ANALYSISRainfall (mm)18016014012010080604020024 May 200931 May 20097 June 200914 June 200921 June 200928 June 20095 July 200912 July 2009AWS Rainfall (mm)Groundwater level (mmAHD)Figure 7: Daily peak tide and STP inflow data19 July 200926 July 20092 August 20099 August 200916 August 200923 August 200930 August 20096 September 200913 September 200920 September 200927 September 20094 October 200911 October 200918 October 200925 October 20091 November 20098 November 200915 November 200922 November 200929 November 20096 December 200913 December 2009Sewage Inflow to STP - current (kL/d)Max daily tide (mm)6000500040003000200010000Inflow (kL/d) and Groundwater Table (mmAHD) and maxdaily tide (km)2.6 Summary of Part 1The analysis undertaken for Part 1 of this study shows that:Maximum instantaneous STP inflow is affected by surging past the step screen and shows nosignificant relationship to the daily STP inflow;Rainfall events have a significant impact on groundwater levels. The duration and magnitudeof this effect depends on the magnitude, duration and frequency of rain days;Periods of high STP inflow correspond with periods of high groundwater table and wetweather;During dry weather, the STP inflow remains relatively constant with non-holiday loading atapproximately 1.063 ML/d;The effect of holiday loads on STP inflows is not as significant as the effect of wet weather;andTides do not have a significant impact on groundwater level or STP inflows.Evans STP Flow Analysis Interim Report Rev 1.doc Page 10

EVANS HEAD STP FLOW ANALYSIS2.7 Current STP FlowsData on sewerage system design flows and STP design criteria are shown in Table 1.Table 1: Sewerage System and STP Design Flow DataSewerage System LoadsSourceA Evans Head (including 20% holiday load) 3,659 EP GHD 2008b, p66B Woodburn (including 20% holiday load) 601 EP GHD 2008b, p66C Total Connected Load 4,260 EP C = A + BD Permanent Load 3,550 EP D = C/1.2E Holiday Population 710 EP E = C - DF Dry weather loading rate 290 L/EP/d Commerce, 2005G Dry weather load (permanent) 1.03 ML/d G = F x DH Dry weather load (holiday) 0.21 ML/d H = F x EI Peak dry weather load 1.24 ML/d I = G + HData from the analysis of historical STP inflows (Part 1) are shown in Table 2. From Section 2.3, thedry weather STP inflow is 1.063 ML/d which agrees closely with the design dry weather permanentload for the STP (1.03 ML/d).Table 2: Historical STP Inflow DataHistorical STP InflowsSourceJ Dry weather, low groundwater, non-holiday period flow 1.063 ML/d Section 2.3K Calculated loading rate 299 L/EP/d K = J / DL Wastewater generation rate 170 L/EP/d GeoLINK, 2009 1M Wastewater generation (permanent population) 604 kL/d M = L x DN Dry weather groundwater infiltration 460 kL/d N = J – MO Calculated dry weather groundwater infiltration loading 129 L/EP/d O = K – LP Wastewater generation (holiday period) 724 kL/d P = L x CQ Dry weather, low groundwater, holiday period flow 1.18 ML/d Q = P + N1. GeoLINK (2009) estimated the dry weather loading rate from indoor water consumption estimates includingwater demand assessments for the Rous Water supply area and standard design rates. GeoLINK (2009)estimated the dry weather groundwater infiltration from the November 2007 and November 2008 inflow as434kL/d, which is similar to the result in Table 2 (460 kL/d).Evans STP Flow Analysis Interim Report Rev 1.doc Page 11

EVANS HEAD STP FLOW ANALYSISThe dry and wet weather components of the current STP flows are shown in Figure 8. The dryweather flow is the sum of the wastewater generation and dry weather groundwater infiltration for thepermanent population and holiday periods (from Table 2). The remainder of the STP inflow isinfluenced by wet weather. The “modelled” total inflow is the sum of the average dry weather flow andthe wet weather flows. There are a few occasions where flows lower than the calculated dry weatherflow (from Table 2) were measured at the STP. This is because the base flow during dry weather is attimes below the average for this period, due to random variation. The variance is not significant whencompared to the total flow and the more influential variables. This is considered to be the mostappropriate approach for the basis of further calculations.Evans STP Flow Analysis Interim Report Rev 1.doc Page 12

EVANS HEAD STP FLOW ANALYSIS1805000Rainfall (mm)160140120100806040200Figure 8: Components of Current STP inflowAWS Rainfall (mm)Sewage Inflow to STP - current (kL/d)Wet weather inflow - current (kL/d)16/10/200715/11/200715/12/200714/01/200813/02/200814/03/200813/04/200813/05/200812/06/200812/07/200811/08/200810/09/200810/10/20089/11/20089/12/20088/01/20097/02/20099/03/20098/04/20098/05/20097/06/20097/07/20096/08/20095/09/20095/10/20094/11/20094/12/20093/01/20102/02/2010Holiday PeriodsAverage Dry Weather Flow - current (kL/d)Modelled Total Inflow - current (kL/d)Evans STP Flow Analysis Interim Report Rev 1.doc Page 13450040003500300025002000150010005000Inflow (kL/d) and Groundwater Table (mmAHD)

EVANS HEAD STP FLOW ANALYSIS3. PART 2 – PREDICTION OF FUTURE INFLOWSThe STP inflow consists of:1. Dry weather flows - Wastewater generated by the population (permanent and/or holidayperiods) and groundwater infiltration during dry weather; and2. Wet weather flows - Additional sewage flows during wet weather including additional inflowand infiltration loading.During some dry times the flow is greater than the calculated dry weather flow. Some of this israndom variability similar to why actual dry weather flows drop below the modelled average. For thepurposes of this report, any flow greater than the dry weather flow is considered to be wet weatherflows to which future inflow/infiltration reduction targets will be applied.3.1 Future Dry Weather Flows3.1.1 Wastewater GenerationThe Evans Head and Woodburn sewerage systems will be augmented to cater for future flows. It isanticipated that Broadwater will be connected to the Evans Head sewerage system by 2014. Thesystem is designed as a pressure sewerage system with a design loading rate of 210 L/EP/d (GHD,2007).Design data for the augmented systems are shown in Table 3.Table 3: Future EP Loads (GHD, 2008b)Town Existing 2010Load (EP)2014 Load(EP)2025 Load(EP)2032 Load(EP)2050 Load(EP)Woodburn 601 624 a 687 768 a 975Evans Head 3,659 4,244 a 6,483 6,777 a 7,532Broadwater - 658 809 a 905 1,170Total b 4,918 5,694 7,979 8,449 9,677Permanent Population 3,550 4,855 6,784 7,192 8,259Holiday Population 710 839 1,195 1,257 1,418a. assuming linear variation between yearsb. Includes 20% holiday loading for Evans Head and Woodburn. Holiday population for Broadwater is assumedto be negligible.Evans STP Flow Analysis Interim Report Rev 1.doc Page 14

EVANS HEAD STP FLOW ANALYSISFuture wastewater flows for the augmented systems are shown in Table 4.Table 4: Future Wastewater FlowsTown Existing 2010Flow (kL/d)2014 Flow(kL/d)2025 Flow(kL/d)2032 Flow(kL/d)2050 Flow(kL/d)Woodburn and EvansHead - permanentWoodburn and EvansHead - holidays604 713 a 1,016 1,069 a 1,205724 856 a 1,219 1,283 a 1,446Broadwater - 112 138 a 154 199Total – permanent 604 825 1,153 1,223 1,404Total – holidays 724 856 1,219 1,283 1,446a. assuming linear variation between years3.1.2 Dry Weather Groundwater InfiltrationFrom Table 2, the dry weather groundwater infiltration is currently 460 kL/d (129 L/EP/d).Council is aiming to reduce sewerage system infiltration through a long-term mains relining program.The effectiveness of this program is not expected to be observed until full relining of each seweragesystem catchment is completed. It is a 50 year program and Council believes the infiltration could bereduced by about 50% at the end of this program. For the purposes of this report, the inflow/infiltrationreduction will reduce by 40% between 2010 and 2050 (40 years).Dry weather groundwater infiltration from the Broadwater system is assumed to be 40 L/EP/d (designloading rate of 210 L/EP/d less wastewater generation rate of 170 L/EP/d).Future dry weather groundwater infiltration for the systems is shown in Table 5. This assumes 1%p.a. reduction in infiltration for Evans Head and Woodburn systems and constant infiltration (per EPconnected) for Broadwater. The infiltration from future sewerage connections in Evans Head andWoodburn is assumed to be negligible as the infrastructure will be new and potentially a pressuresystem design (with low infiltration).Table 5: Future Dry Weather Groundwater InfiltrationTown Existing 2010(kL/d)2014 (kL/d) 2025 (kL/d) 2032 (kL/d) 2050 (kL/d)Woodburn and EvansHead460 442 395 369 308Broadwater - 26 32 36 47Total 460 468 428 405 354Evans STP Flow Analysis Interim Report Rev 1.doc Page 15

EVANS HEAD STP FLOW ANALYSIS3.1.3 Current and Future Dry Weather FlowsFrom the above analysis, the dry weather flow components are shown in Table 6.Table 6: Dry Weather Flow ComponentsComponent Existing 2010 (kL/d) 2050 (kL/d)Wastewater generation - permanent 604 1,404Wastewater generation - holidays 724 1,446Dry weather groundwater infiltration 460 354Total – permanent 1,063 1,758Total – holidays 1,184 1,801Figure 9 shows the average dry weather flow in 2010 (current flows) and the calculated average dryweather flow for 2050 (permanent population and holiday periods) applied to the historicalhydrological period utilised in this study (October 2007 to February 2010). Figure 9 indicates theaverage calculated dry weather flows. Random variation around these averages will occur but cannotbe modelled meaningfully.STP Inflow (kL/d)2000190018001700160015001400130012001100100090080070060050016/10/200715/11/200715/12/200714/01/200813/02/200814/03/200813/04/200813/05/200812/06/200812/07/200811/08/200810/09/200810/10/20089/11/20089/12/20088/01/20097/02/20099/03/20098/04/20098/05/20097/06/20097/07/20096/08/20095/09/20095/10/20094/11/20094/12/20093/01/20102/02/2010Holiday Periods Average Dry Weather Flow - current (kL/d) Average Dry Weather Flow - 2050 (kL/d)Figure 9: Current and future dry weather flowEvans STP Flow Analysis Interim Report Rev 1.doc Page 16

EVANS HEAD STP FLOW ANALYSIS3.2 Future Wet Weather FlowsThe additional STP flows during wet weather are significantly affected by rainfall and groundwaterinfiltration. Council’s infiltration reduction program is expected to result in decreased wet weatherflows in future, as for the dry weather groundwater infiltration (refer Section 3.1.2, i.e. 40% reductionbetween 2010 and 2050). The current (2010) and future (2050) wet weather flow components areshown in Figure 10 for the time period used in this analysis (October 2007 to February 2010).400035003000STP Inflow (kL/d)2500200015001000500016/10/200715/11/200715/12/200714/01/200813/02/200814/03/200813/04/2008Wet weather inflow - current (kL/d)13/05/200812/06/200812/07/200811/08/200810/09/200810/10/20089/11/20089/12/20088/01/20097/02/20099/03/20098/04/20098/05/20097/06/20097/07/20096/08/20095/09/20095/10/20094/11/20094/12/2009Wet weather inflow - 2050 (kL/d)Figure 10: Current and future (showing a 40% reduction) wet weather flow (excludingwastewater generated by the population)3.3 Future STP Inflow3/01/20102/02/2010The predicted future (2050) inflow series was created through the recombination of the followingelements: Population generated wastewater flows, adjusted for growth (refer Table 4);Dry weather groundwater infiltration, reduced by 40% over 40 years (refer Table 5); and Wet weather flows, reduced by 40% over 40 years (Section 3.2).A time series of the total future STP inflows (compared to modelled current flows) is shown in Figure11 for the time period used in this analysis (October 2007 to February 2010).Evans STP Flow Analysis Interim Report Rev 1.doc Page 17

EVANS HEAD STP FLOW ANALYSIS5000450040003500STP Inflow (kL/d)30002500200015001000500016/10/200715/11/200715/12/200714/01/200813/02/200814/03/2008Modelled Total Inflow - current (kL/d)Figure 11: Total future STP inflow13/04/200813/05/200812/06/200812/07/200811/08/200810/09/200810/10/20089/11/20089/12/20088/01/20097/02/20099/03/20098/04/20098/05/20097/06/20097/07/20096/08/20095/09/20095/10/20094/11/20094/12/20093/01/20102/02/2010Sewage Inflow to STP - 2050 (kL/d)Evans STP Flow Analysis Interim Report Rev 1.doc Page 18

EVANS HEAD STP FLOW ANALYSIS4. PART 3 – ANALYSIS OF STP INFLOW AND OUTFLOWThe STP inflow (not including recycled flows) and effluent flows are shown in Figure 12. The inflowand outflow follow a similar trend although there is more variation in outflows on a daily basis.There are currently no on-site reuse or irrigation activities at the STP and the rate of evaporation fromthe process tanks is likely to be lower or equivalent to direct rainfall input. Flows from the STP hardstand areas are recycled through the plant. Theoretically, the inflow and outflow will be the sameapart from the additional sewage generated by the site office (which is included in the drainage pumpstation flows) and the additional flow due to rainfall captured at the STP.STP treatment processes and cycling as well as operator control of flows influence the outflows on adaily basis and accounts for much of the variability between inflows and outflows.60005000STP Flow (kL/d)4000300020001000016/10/200715/11/200715/12/200714/01/200813/02/200814/03/200813/04/2008Sewage Inflow to STP - current (kL/d)Figure 12: STP inflow and outflow13/05/200812/06/200812/07/200811/08/200810/09/200810/10/20089/11/20089/12/20088/01/20097/02/20099/03/20098/04/20098/05/2009STP Discharge - current (kL/d)7/06/20097/07/20096/08/20095/09/20095/10/20094/11/20094/12/20093/01/20102/02/2010To determine the relationship between inflows and outflows, the daily flows, 2-day average flows and3-day average flows were compared as shown in Figure 13. The degree of scatter in the plot is lowerwith the 2-day averages and reduces again with the 3-day average indicating that the variationbetween daily inflows and outflows reduces over a 2-3 day period.A linear trendline for the 3-day average flows is also shown. The R 2 value (which can be interpretedas the proportion of the variance in 3-day average inflow attributable to the variance in 3-day averageoutflow) is 0.9575 (i.e. > 95%). This combined with the successive convergence of the inflow/outflowEvans STP Flow Analysis Interim Report Rev 1.doc Page 19

EVANS HEAD STP FLOW ANALYSISrelationship with longer periods indicates water balance is achieved and that inflows are a goodpredictor of outflows.500045004000y = 0.9512x + 66.963R 2 = 0.95753500STP inflow (kL/d)3000250020001500100050000 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500 5,000STP outflow (kL/d)Daily flows 2-day average flows 3-day average flows Linear (3-day average flows)Figure 13: Daily inflow and outflowThe data show that over a 2-3 day period, all STP flows are discharged from the STP, although thereis some influence of attenuation, cycling and pumping regimes on a daily basis.Data on total and average daily volumes over the period of record (861 days) are shown in Table 7.This shows that the total inflows are discharged from the STP over the period of record.Table 7: Total Volume (over 861 days) and Average Daily STP FlowsFlow Total (ML) Daily Average (ML/d)Sewage Inflow to STP (not including recycledflows)1,301 1.510STP Outflow 1,299 1.520Difference between Inflow and Outflow 2 0.010The minor reduction in outflow is assumed to be losses such as sludge removal and drying and/ormetering errors. For the purposes of this project and the assessment of discharges to the EvansRiver, the future effluent flows can be adequately represented by the future STP inflows establishedin Part 2 (Section 3) of this report.Evans STP Flow Analysis Interim Report Rev 1.doc Page 20

EVANS HEAD STP FLOW ANALYSIS5. PART 4 – FUTURE EFFLUENT FLOW SCENARIOS5.1 Continuous DischargeThe data from Figure 11 represent the future (2050) STP inflows to the STP and hence the future(2050) effluent flows assuming the current STP discharge system (no additional storage and currentpumping regime).The peak daily flow of effluent discharged from the STP can be reduced through the provision ofstorage and/or a modified pumping regime.5.2 Potential Transfer System OptionsThe water balance undertaken for the reuse scheme options investigation (GeoLINK, 2009) indicatesthat there is 670 kL of buffer storage available in the existing balance tanks. The designed reusescheme for Evans Head and Woodburn also included a proposed STP dam of volume 7.02 ML (totalvolume 8.28 ML). An additional reservoir for disinfected recycled water of 1 ML was also proposed.This gives a total potential storage at the STP of 8.69 ML. At this stage, it has been assumed that thesite constraints will not allow additional storage at the STP. The design of the STP dam could bemodified to provide additional storage, however, at this stage it is assumed that the maximum storageavailable at the STP prior to transfer is 8.69 ML.Additional storage may be provided at the Evans River discharge site or through a wetland/forest priorto discharge to the River. However, site constraints have not been considered for this report.The existing installed pumps operate at a maximum flow of 266 L/s against a pumping head of 7.5m.Pumping options include retaining the existing pumps, modification of the existing pumps (e.g.impellers or motors), addition of booster pumps or replacement of the pumps. Hydraulic analysis ofthe transfer system/storage options has not been undertaken for this report. If any scenarios areconsidered feasible by BMT WBM, concept development of the transfer system would be undertakenas a subsequent step.5.3 Ebb-Tide DischargePreliminary advice from BMT WBM has indicated that the applicable ebb-tide is 4 hours on the hightide and 2 hours on the low tide (i.e. a total of 6 hours per day). On average, an ebb-tide dischargecan therefore operate for 6 hours or one quarter of the day. This does not consider any diurnal tidal orflow variations. Further inspection of the estuary hydrodynamic model and refinement of theappropriate ebb tide discharge period may require modification of the scenarios considered below.5.4 Scenario AnalysisFor the scenario analysis, a simple daily water balance was undertaken using the 2050 STP inflows.For the water balance, the arrangement shown in Figure 14 was assumed. The priority for effluentdisposal is:Evans STP Flow Analysis Interim Report Rev 1.doc Page 21

EVANS HEAD STP FLOW ANALYSIS1. Disposal to Evans River (daily volume limited by discharge rate and duration);2. Post-transfer storage (used when inflow is greater than the discharge rate);3. Pre-transfer (STP) storage (used after post-transfer storage is full); and4. Emergency overflow to Salty Lagoon (when storages are full and inflow is greater than thedischarge flow).It is assumed that the transfer system does not limit the discharge (i.e. the pump/pipe arrangementcan be designed to discharge the required flows).EffluentpumpsInflow STP STP DamBooster/transferpumpPost-transferstorageSaltyLagoonEvans RiverFigure 14: Effluent Transfer to Evans River5.5 ResultsThe assumptions and results for each scenario are shown in Table 8. These scenarios provide arange of results in terms of flows to Evans River, overflow to Salty Lagoon, storage capacity anddischarge rate. The results show that the provision of additional post-transfer storage (Scenario 6compared to Scenario 4) does not significantly reduce the overflow to Salty Lagoon. However,increasing the allowable daily discharge rate allows the transfer of more peak flows (Scenario 3 and 7compared to Scenario 4 and 5).The daily discharge to the Evans River for each scenario is shown in Figure 15. The daily time seriesresults for Scenarios 1 and 7 are the same and only Scenario 1 has been shown here. Similarly, dailydischarge results for Scenarios 2 and 3 are the same. Daily discharge results for Scenarios 4 and 6are similar.Evans STP Flow Analysis Interim Report Rev 1.doc Page 22

EVANS HEAD STP FLOW ANALYSISTable 8: Future Flow ScenariosScenarioPre-Post-AllowableAllowableMax.Overflow toAverage(ultimate, 2050transfertransferriverdailyvolumeSaltyoverflowSTP flow)storagestoragedischargedischargetransferredLagoonto Salty(ML)(ML)periodratefrom STP(days perLagoon(hr/d)(ML/d)(ML/d)year, % of(ML/d)time)1 Continuousdischarge12 Continuousdischarge20 0 24 4.0 3.94 0 08.69 0.2 24 2.5 2.70 0 03 Ebb-tide 1 8.69 0.2 6 10 2.70 0 04 Ebb-tide 2 8.69 0.2 6 8.0 2.20 101 (28%) 0.095 Ebb-tide 3 8.69 0.2 6 5.0 1.45 358 (98%) 0.776 Ebb-tide 4 8.69 3.0 6 8.0 3.94 96 (26%) 0.087 Ebb-tide 5 8.69 0.2 6 15 3.94 0 04500Effluent Transfer to Evans River (kL/d)40003500300025002000150010005000Scenario 1 - Continuous (0/0ML, 4ML/d)Scenario 5 - Ebb-tide 3 (8.69/0.2ML, 5ML/d)Scenario 4 - Ebb-tide 2 (8.69/0.2ML, 8ML/d)Figure 15: Effluent Transfer to Evans River – Scenario Results16/10/200715/11/200715/12/200714/01/200813/02/200814/03/200813/04/200813/05/200812/06/200812/07/200811/08/200810/09/200810/10/20089/11/20089/12/20088/01/20097/02/20099/03/20098/04/20098/05/20097/06/20097/07/20096/08/20095/09/20095/10/20094/11/20094/12/20093/01/20102/02/2010Scenario 3 - Ebb-tide 1 (8.69/0.2ML, 10ML/d)Scenario 6 - Ebb-tide 4 (8.69/3.0ML, 8ML/d)Evans STP Flow Analysis Interim Report Rev 1.doc Page 23

EVANS HEAD STP FLOW ANALYSISThe daily overflow to Salty Lagoon for Scenarios 4, 5 and 6 and the daily rainfall are shown in Figure16. The overflow in Scenarios 1, 2, 3 and 7 is zero.3.00180Flow to Salty Lagoon (ML/d)2.502.001.501.000.5016014012010080604020Rainfall (mm)0.0016/10/2007 14/01/2008 13/04/2008 12/07/2008 10/10/2008 8/01/2009 8/04/2009 7/07/2009 5/10/2009 3/01/20100AWS Rainfall (mm)Scenario 5 - Ebb-tide 3 (8.69/0.2ML, 5ML/d)Scenario 4 - Ebb-tide 2 (8.69/0.2ML, 8ML/d)Scenario 6 - Ebb-tide 4 (8.69/3.0ML, 8ML/d)Figure 16: Overflow to Salty Lagoon – Scenario Results5.6 Summary of Part 4The time series data for effluent transfer to the Evans River (2050 flows for the period of analysis) willbe provided to WBM BMT for input into the hydrodynamic and water quality models. For the initialmodel runs, base scenarios for continuous release and ebb-tide release are required.As discussed in Section 5.4, it is assumed that the overflow to Salty Lagoon should be minimised byprioritising discharge to the Evans River. Therefore, Scenarios 4, 5 and 6 will not be considered forthe initial model runs.In terms of flow to the Evans River, the results for Scenarios 1 and 7 and Scenarios 2 and 3 are thesame. On this basis, Scenarios 1 (Continuous) and 3 (Ebb-tide) will be presented as the initialscenarios to be incorporated into the BMT WBM hydrodynamic modelling (refer Figure 17).Evans STP Flow Analysis Interim Report Rev 1.doc Page 24

EVANS HEAD STP FLOW ANALYSIS4500Effluent Transfer to Evans River (kL/d)4000350030002500200015001000500016/10/200715/11/200715/12/200714/01/200813/02/2008Scenario 1 - Continuous (0/0ML, 4ML/d)14/03/200813/04/200813/05/200812/06/200812/07/200811/08/200810/09/200810/10/20089/11/20089/12/20088/01/20097/02/20099/03/20098/04/20098/05/20097/06/20097/07/20096/08/20095/09/20095/10/20094/11/20094/12/20093/01/20102/02/2010Scenario 3 - Ebb-tide 1 (8.69/0.2ML, 10ML/d)Figure 17: Effluent Transfer to Evans River – Base Scenarios 1 (Continuous) and 3 (Ebb-tide)Evans STP Flow Analysis Interim Report Rev 1.doc Page 25

EVANS HEAD STP FLOW ANALYSISREFERENCESNSW Department of Commerce (2005) Detailed Concept Development for the Evans Head SewageTreatment Plant AugmentationGeoLINK (2009) Evans Head & Woodburn Water Recycling Scheme, Assessment of SchemeOptionsGHD (2007) Richmond Valley Council, Broadwater Sewerage Scheme Detailed Design - DesignOptions ReportGHD (2008a) Richmond Valley Council, Report on Review of Woodburn Sewerage AugmentationStrategyGHD (2008b) Richmond Valley Council, Report on Review of Evans Head Sewerage AugmentationStrategyEvans STP Flow Analysis Interim Report Rev 1.doc Page 26

CREATING A WATERCAST CATCHMENT MODEL C-1APPENDIX C: CREATING A WATERCAST CATCHMENT MODELTo construct a catchment model within WaterCAST requires the user to define which modelcomponents are required and how they should be linked together. The underlying data within themodel is a spatial description of the catchment, whether simply a subcatchment map, or a digitalelevation model. These are then joined together via a node-link network, which is then parameterisedand calibrated to complete the catchment model. The steps describing the model constructionprocess are outlined below:Step 1 – The catchment and streams are described spatially using either a digital elevation model orfrom topographical data (see Figure 1 using an example catchment).Figure 1 Step 1 - A Spatial Description of the CatchmentStep 2 – A node-link network is built either automatically from the digital elevation model, or manuallyfrom the data obtained in Step 1 (see Figure 2 using an example catchment).G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CREATING A WATERCAST CATCHMENT MODEL C-2Figure 2 Step 2 – Construction of a Node-Link NetworkStep 3 – Information about each subcatchment is described and within this step, land use data isused to describe the “Functional Units” within each subcatchment where different ones haveparticular runoff and constituent generation characteristics. These are typically a common set for theentire catchment, though the extent differs within each subcatchment. When the functional units(FUs) are defined, constituents are then selected that will be common across all subcatchments andfunctional units (see Figure 3 using an example catchment).Figure 3 Step 3 - Definition of Functional Units (Land Uses)Step 4 – Particular models are selected which are best suited to the subcatchment/node and thesethen describe (through different parameters) how each functional unit responds to climatic inputs (seeFigure 4).G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CREATING A WATERCAST CATCHMENT MODEL C-3Figure 4 Step 4 - Selection of Node ModelsStep 5 – Each link in the stream network is defined using an appropriate model in a similar way to thesubcatchments in Step 4 inputs (see Figure 5).Figure 5 Step 5 – Selection of Link ModelsThese link models are combined with the models describing the subcatchments/nodes so that groupsof models are linked together to describe the catchment as shown in Figure 6.Figure 6 Node and Link Models Describe the CatchmentG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CREATING A WATERCAST CATCHMENT MODEL C-4Step 6 – Climatic data is selected. This can be either from individual stations, or interpolated griddeddata (e.g. SILO, PET Atlas). The WaterCAST framework then interrogates this data for each modelrun performed (see Figure 7).Figure 7 Step 6 - Climatic Data from SILO/BOM Climate GridsStep 7 – Parameterisation. This is usually accomplished through comparison with some observeddata, such as flow gauging stations and storm event water quality as illustrated in Figure 8, if this datais available. Alternatively, generally accepted values based on similar studies in similar areas areutilised. It is noted that there are no existing flow gauges or catchment runoff water quality data forthe Evans River catchment.Figure 8 Step 7 - Model ParameterisationG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

CREATING A WATERCAST CATCHMENT MODEL C-5Once the model has been appropriately parameterised, and then checked through calibration, it isready for use. In most cases, the model is set up to represent an existing case. A screenshot fromWaterCAST showing catchments, nodes and links of the Evans River model is shown in Figure 9Figure 9 Evans River WaterCAST ModelResults of various scenarios can then be extracted for all constituents used in the model anddisplayed on screen, or exported to other programs such as Excel for compilation or post-processing.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WATERCAST WATER QUALITY ASSESSMENTS D-1APPENDIX D: WATERCAST WATER QUALITY ASSESSMENTSCatchment water quality modelling in WaterCAST is included in this appendix as a potential tool forrefinement of the Evans River water quality modelling. Because monitoring data were not collected insupport of calibration of this module for modelling, these results were not included as inputs ofcatchment modelling to the Evans River water quality model.WaterCAST Water QualityThe WaterCAST modelling framework currently supports a limited range of pollutant generationprocesses including (Argent et al 2008b):• Event Mean Concentration (EMC) / Dry Weather Concentration (DWC);• Export coefficient/export rate (t/ha/yr); and• Observed constituent.The EMC/DWC pollutant generation process was selected in the current application and is commonpractice for many daily time step catchment water quality models. The observed constituent modelrequires extensive data sets across the entire catchment (normally unavailable) and the exportcoefficient model does not account for changes in runoff between years or between locations within acatchment which may receive higher or lower rainfall. The EMC/DWC model addresses both ofthese limitations by allowing the estimation of pollutant loads from runoff. The EMC/DWC modelhowever has the key limitation in that it cannot be used to model water quality for particular stormevents. This model does however facilitate the estimation of long term or mean annual pollutantexports and should be interpreted in this way.In the present study, literature values have been used to derive and allocate EMC/DWC values foreach land use represented by the model and apply these EMC/DWC values across the entirecatchment area. As more information is collated and data analysis is undertaken in the catchment,we would expect that modification of the EMC/DWC values for individual land uses in individualsubcatchments would be undertaken.Extensive research and analysis of local water quality data has been carried out by Chiew andScanlon (2002) to determine land use based EMC and DWC values for the south-east Queenslandregion. The median values from this study have been used, and are shown in Table 1.Total suspended solids, total nitrogen and total phosphorous EMCs for the sugar cane land use havebeen derived from Masters et al (2008) (as mean concentrations 21 days after fertiliser application,from 67 mm of simulated rainfall at 100 mm/hr). South-east Queensland dry weather concentrationsfor agricultural land use have been adopted for sugar cane in this study (Table 1). Rainfall EMCvalues sourced from WBM (2003).G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WATERCAST WATER QUALITY ASSESSMENTS D-2Table 1 EMC and DWCs for TSS, TN and TP for the Evans River WaterCAST modelTSS TN TPLand Use NameEMC(mg/L)DWC(mg/L)EMC(mg/L)DWC(mg/L)EMC(mg/L)DWC(mg/L)Forest 20 7 1.5 0.4 0.06 0.03Grazing 260 10 2.08 0.7 0.3 0.07Horticulture 300 10 1.95 0.7 0.32 0.07Intensive Use 130 7 1.6 1.5 0.28 0.11Road 130 7 1.6 1.5 0.28 0.11Rural Residential 130 10 1.6 0.7 0.28 0.07Sugar Cane 125 10 7.3 0.7 0.72 0.07Urban 130 7 1.6 1.5 0.28 0.11Water (Rainfall) 0 0 0.4 0 0.006 0Observed concentrations for TSS, TN and TP have been included in the model at the same node asthe inflow time series for the Tuckombil Canal to take into consideration pollutants within theRichmond River that may contribute significantly to the total pollutant load in the Evans River. Thesevalues have been adopted from Patterson Britton & Partners (1999) and are shown in Table 2.Table 2 Observed concentrations for TSS, TN and TP for the Tuckombil Canal Weir OverflowConstituent TSS TN TPObserved Concentration (mg/L)* 280 0.88 0.15*Richmond Overflows: Section 6.5.2-Table 6.9.Model ResultsThe final Evans River WaterCAST model layout is shown in Figure 4-4. Within the WaterCASTmodel estimated flows and constituent loads can be extracted at any node, link or subcatchment inthe model domain. Key model outputs presented for the existing case scenario include:• Estimated mean annual flows and constituent loads;• Estimated mean annual land use constituent loads (kg/ha/yr); and• Temporal variability in flows and constituent loads.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WATERCAST WATER QUALITY ASSESSMENTS D-3Figure 1 Evans River WaterCAST ModelEstimated Total and Mean Annual Flows and LoadsModelled total flows and loads over the period January 2000 to December 2009 are provided in Table3. This table shows total flows and loads from the Evans River catchment with and without theinclusion of the Tuckombil Canal inflows.Table 3 Estimated Total Flows and Loads from Evans River and via Tuckombil CanalSourceFlow TSS TN TPML Percent Tonne Percent Tonne Percent Tonne PercentEvans RiverCatchment Flows406,000 51% 21,800 15% 560 68% 45 44%Tuckombil CanalInflows387,000 49% 126,700 85% 270 32% 58 56%Total Outflow 793,000 100% 148,500 100% 830 100% 104 100%Estimated Mean Annual Land Use Constituent LoadsModelled mean annual pollutant loads from each land use are presented in Table 4. This table alsoprovides the percentage that each land use contributes to the overall pollutant load from thecatchment. Figure 2 presents the loads contributed by each land use (pollutant averaged).G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WATERCAST WATER QUALITY ASSESSMENTS D-4Table 4 Mean Annual Pollutant Loads by Land UseLand UseFlow TSS TN TPML/yr Percent T/yr Percent kg/yr Percent kg/yr PercentForest 26,270 65% 469 22% 34,650 61% 1,450 32%Grazing 4,010 10% 878 40% 7,430 13% 1,050 23%Horticulture 20 0% 4 0% 30 0% 5 0%Intensive Use 2,840 7% 362 17% 4,540 8% 790 17%Road 420 1% 54 2% 680 1% 120 3%Rural Residential 1,810 4% 210 10% 2,710 5% 460 10%Sugar Cane 490 1% 52 2% 3,050 5% 300 7%Urban 1,210 3% 149 7% 1,930 3% 330 7%Water 3,520 9% - 0% 1,410 2% 20 0%Total 40,610 2,179 56,440 4,520ForestGrazingHorticultureIntensive UseRoadRural ResidentialSugar CaneUrbanWaterFigure 2 Mean Pollutant Loads Contributed by Land Use (averages for TN, TP and TSS)Estimated Mean Annual Areal Land Use Constituent LoadsAreal land use load estimates were derived by dividing the mean annual load (mean annual loadsprovided in Table 4) by the respective land use area. This provides mean annual areal loads asshown in Table 5. A graphical comparison is provided in Figure 3, Figure 4 and Figure 5.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WATERCAST WATER QUALITY ASSESSMENTS D-5Table 5 Mean Annual Areal Pollutant Loads by Land UseLand Use Area (ha) TSS (Kg/ha/yr) TN (Kg/ha/yr) TP (Kg/ha/yr)Forest 7,123 66 4.9 0.2Grazing 1,084 810 6.9 1.0Horticulture 5 833 6.3 1.0Intensive Use 290 1,248 15.7 2.7Road 43 1,247 15.7 2.8Rural Residential 390 538 6.9 1.2Sugar Cane 133 391 22.9 2.3Urban 174 858 11.1 1.9Water 246 - 5.7 0.1Total 9,488 230 5.9 0.5TSS (Kg/ha/yr)1,4001,2001,000800600400200‐Figure 3 Mean Annual Areal TSS Load25.020.0TN (Kg/ha/yr)15.010.05.0‐Figure 4 Mean Annual Areal TN LoadG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WATERCAST WATER QUALITY ASSESSMENTS D-625.020.0TP (Kg/ha/yr)15.010.05.0‐Figure 5 `Mean Annual Areal TP LoadTemporal RepresentationYearModelled annual flows and loads as delivered from the Evans River Catchment and Tuckombil Canalare provided in Table 6. This table also shows the total and mean annual flow and load from theEvans River catchment. This data includes the Tuckombil Canal inflows.Table 6 Estimated Total Annual and Mean Flows and Loads from Evans River Catchment andTuckombil Canal (2000 –2009)Flow (ML) TSS (Tonne) TN (Kg) TP (Kg)Evans RiverCatchmentTuckombilCanalEvans RiverCatchmentTuckombilCanalEvans RiverCatchmentTuckombilCanalEvans RiverCatchmentTuckombilCanal2000 20,900 200 1,100 900 27,000 - 2,300 1002001 46,800 78,800 2,500 24,200 66,000 57,000 5,200 11,8002002 11,800 100 600 500 14,000 - 1,300 -2003 38,500 200 2,000 1,800 53,000 - 4,200 1002004 26,000 9,600 1,400 3,800 34,000 4,000 2,900 1,5002005 46,800 29,300 2,600 10,300 68,000 16,000 5,300 4,4002006 55,300 23,500 2,900 9,100 77,000 10,000 6,100 3,6002007 27,900 200 1,500 1,200 38,000 - 3,200 -2008 57,200 42,400 3,000 14,500 79,000 26,000 6,300 6,4002009 74,700 203,000 4,100 60,400 108,000 156,000 8,300 30,500Total 406,000 387,000 22,000 127,000 564,000 269,000 45,000 58,000MeanAnnual40,600 38,700 2,200 12,700 56,400 26,900 4,500 5,800Figure 6 shows the estimated total annual flows from the Evans River catchment. Estimations ofcatchment pollutant exports of TSS, TN and TP are shown in Figure 7, Figure 8 and Figure 9,respectively.Over the 10 year period assessed, it was found that catchment inflows accounted for approximately15% of Total Suspended Solids, 68% of Total Nitrogen and 44% of Total Phosphorus (TP) loadingsto the Evans River. This is consistent with the findings of the Estuary Processes Study (PBP, 1999a)G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WATERCAST WATER QUALITY ASSESSMENTS D-7which indicates that the catchment contributed around 17% of TSS, 57% of the TN loads and 57% ofthe TP loads to the Evans River.300,000250,000Evans River Catchment Tuckombil Canal Rainfall2,5002,000ML/Year200,000150,000100,00050,0001,5001,000500Rainfall (mm)‐2000 2001 2002 2003 2004 2005 2006 2007 2008 2009Year‐Figure 6 Estimated Annual Flows70,000,00060,000,00050,000,000Evans River CatchmentTuckombil CanalTSS (Kg/Year)40,000,00030,000,00020,000,00010,000,000‐2000 2001 2002 2003 2004 2005 2006 2007 2008 2009YearFigure 7 Estimated Annual TSS LoadsG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WATERCAST WATER QUALITY ASSESSMENTS D-8180,000160,000140,000Evans River CatchmentTuckombil CanalTN (Kg/Year)120,000100,00080,00060,00040,00020,000‐2000 2001 2002 2003 2004 2005 2006 2007 2008 2009YearFigure 8 Estimated Annual TN Loads35,00030,00025,000Evans River CatchmentTuckombil CanalTP (Kg/Year)20,00015,00010,0005,000‐2000 2001 2002 2003 2004 2005 2006 2007 2008 2009YearFigure 9 Estimated Annual TP LoadsResults SummaryThe WaterCAST model has been developed using available data. As previously mentioned, limitedflow and water quality data is available to make an accurate prediction of flows and pollutant loadsfrom the catchment. Flows and loads presented in this section are suitable for use in this study,taking into considerations its limitations.As can be seen, a large proportion of flows discharging from Evans River, particularly in 2001 and2009, enter upstream as inflows from Tuckombil Canal. These modelled flows are highly variablefrom year to year and are dependent on large rainfall events and Tuckombil Canal inflows. The higherG:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

WATERCAST WATER QUALITY ASSESSMENTS D-9variability observed in the annual pollutant load plots correspond to higher runoff years indicating ahigher proportion of event based runoff (and associated pollutant load) rather than base flows duringthese years.The majority of suspended solid loads are attributed to the Tuckombil Canal inflows through mostyears. Total nitrogen loads, on the other hand, are associated with runoff from the surroundingcatchment. The majority of total phosphorous loads are associated with runoff from the surroundingcatchment in all years except for 2001 and 2009 where large Tuckombil Canal inflows result in asignificant increase in TP loads.The contribution of the forest and grazing lands to the overall constituent loads coming from the studycatchment area is evident (excluding Tuckombil Canal). However, when based on area, sugar cane,road and intensive land uses contribute significantly to pollutant loads.The limitations of the model (i.e. inability to use locally specific data for the purposes of calibration)could be reduced by catchment specific event load monitoring, for individual land use classes. Thismonitoring and data interpretation would provide better pollutant export load predictions within thecatchment, however, given the variability noted within the report, this would have to be collected overan extended period in order to derive suitable, locally applicable parameters. Undertaking this actionwould improve adopted dry and wet weather pollutant export coefficients for various land uses withinthe WaterCAST model to provide better predictions of loads.G:\ADMIN\B17607.G.DCC_EVANSRIVER\R.B17607.001.03.REVISED FINAL.DOC

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