GEOMORPHOLOGY REPORT - CRC LEME

More documents

Recommendations

Info

metre of the ground surface (Chen 1995). The Darling River and its Anabranch also enter the Murray River in this reach at Wentworth, and approximately 15 km west of Wentworth, respectively. 3 KEY LAND MANAGEMENT QUESTIONS The main identified issue in this iconic reach of the Murray River is the downstream impact of salt mobilisation during flood recessions. Research to date indicates that the Lindsay and Wallpolla Islands accumulate large amounts of salt during low flow periods and that significant floods could act to liberate much of this salt, moving it downriver where it could severely affect agricultural areas in South Australia. Accordingly, the key identified requirements are the design of an environmental watering regime and planning of revegetation strategies to optimise floodplain health and limit the salinity impact on the Murray River. This will entail gaining a more detailed understanding of the floodplain characteristics, including flush zones and salt stores. Identification of major salt influxes to the river and possible interception zones is also desired. These concerns can be expressed in the following questions (from Lawrie 2006), with conceptual geophysical targets shown in Figure 3. Figure 4 shows a cross-section of the Murray River floodplain and Wallpolla Island. 1. What is the potential for salt mobilisation during Living Murray inundation actions? This requires identifying holes in the Coonambidgal Formation – target 1. Salt stored in the sub-surface (targets 2 and 5 in the model below) may be mobilised through connected pathways to the river and surface (through targets 1 and 3). This question addresses the act of mobilisation and is therefore concerned with the source or initial position of the salt and what is causing it to move. This requires identifying high salt stores that are at risk of being mobilised. Therefore, we need to identify high conductivity salt stores, particularly in the Coonambidgal Formation and upper Monoman Formation (target 5), and we need to identify low conductivity zones where water preferentially feeds into the floodplain sediments to potentially mobilise these salt stores, namely flush zones (target 3) and floodplain recharge areas (target 1). In the model below. Questions 2 and 3, below, deal with the destination of the mobilised salt. See Figure 3. 2. Delivery of salt to the river. How salt is being delivered to the river requires identification of high salinity zones (similar to previous question) and relatively permeable zones or pathways for groundwater movement back to the river or anabranches once the flood recedes – targets 5, 4 and 2 in Figure 3. Salt being delivered to the river now will be interpreted from mapping salt stores (eg targets 2 and 5) and their connection to the river either directly or indirectly through preferential flow paths. Additionally, salt being delivered to the river will also be mapped by identifying areas where Blanchetown Clay is thin or absent, giving rise to potential higher saline influxes to the river from saline groundwaters in the Loxton- Parilla Sands (target 4 in Figure 3). 3. Understanding of the drivers of floodplain health with respect to groundwater processes. This is matter of identifying elements of floodplain and groundwater processes – targets 1, 2, 3 and 4 in the model below. This is a matter of identifying elements of floodplain composition (including salt), groundwater levels and groundwater processes. AEM can provide important baseline data in resolving this question by defining the distribution of fine and coarse grain floodplain lithologies (target: whole of floodplain, particularly top 5 metres), high salinity zones (target 5), high recharge zones (target 1), flush zones (target 3), permeable pathways delivering salt to prone areas such as anabranches and other depressions (target 2) and exposure to saline fluxes from the Parilla Sand (target 4). Recharge zones (target 1), salt stores (2 and 5) and flush zones (target 3) are conceptualised in Figure 3. 3
4. Identification of the high recharge areas in the floodplain? This relates to question 1, and means identifying areas of the floodplain where water can most easily enter from the surface i.e. high porosity permeability (sand) connected to subsurface – targets 1 and 2 in Figure 3. 5. What is the extent and thickness of the Blanchetown Clay and the Coonambidgal Formation? Extent and thickness of the Blanchetown Clay can be modelled in areas adjacent to the incised valley (targets 4 & 6a in Figure 3) and beneath the incised valley (targets 4 & 6b) where the conductivity contrasts between the Blanchetown Clay and the overlying Monoman Formation are high enough. Targets 1 and 2 (Figure 3) can assist in the determination of the thickness and extent of Coonambidgal Formation. Drill-hole and geomorphic information will be used in the interpretation of the extent and thickness of the Coonambidgal Formation. 6. Where is salt stored in the unsaturated zone? Target 7 in Figure 3. Figure 3. Conceptual model (cross-section) and proposed geophysical targets in the Lindsey – Walpolla area: WF = Woorinen Formation, CF = Coonambidgal Formation, MS = Monoman Sands, BC = Blanchetown Clay, PS = Parilla Sand (Lawrie 2006). Figure 4. Schematic hydrogeological cross-section representing the Lindsay Island reach of the Murray River Floodplain (from SKM 2004). 4
Page 1 and 2: CRCLEME Cooperative Research Centre
Page 3 and 4: This report (CRC LEME Open File Rep
Page 5 and 6: Lindsay and Wallpolla Creeks are si
Page 7 and 8: TABLE OF CONTENTS _Toc224538156 1 I
Page 9 and 10: List of Tables Table 1. Association
Page 11: The main objective of the studies r
Page 15 and 16: The SRTM was used as to provide the
Page 17 and 18: Figure 6. Compartmentalisation of t
Page 19 and 20: Dune on terrace Alluvial terrace Yo
Page 21 and 22: Intermediate floodplain Modern floo
Page 23 and 24: Locations of sample sites are given
Page 25 and 26: 6.1 Granulometry 6.1.1 Methodology
Page 27 and 28: Table 2). Mean pH and EC profiles a
Page 29 and 30: when sampling. This is also reflect
Page 31 and 32: Figure 12. SPOT image of Wallpolla
Page 33 and 34: REFERENCES Bowler, J.M. and Harford
Page 35 and 36: APPENDIX 1. ASTER data and interpre
Page 37 and 38: APPENDIX 2. SPOT Data and interpret
Page 39 and 40: APPENDIX 3. DEM data and interpreta
Page 41 and 42: APPENDIX 4. Gamma-ray data 500000 (
Page 43 and 44: APPENDIX 6. Site Descriptions and D
Page 45 and 46: Site 3 South Settlement road, ~20 m
Page 47 and 48: Site 5 Western end of Keera Road, s
Page 49 and 50: Site 7 Eastern end of Old Mail Rd t
Page 51 and 52: Site 12 Further to west along Old M
Page 53 and 54: Site 14 Dedmens drive, across aband
Page 55 and 56: Site 16 Same area as previous sampl
Page 57 and 58: Site 18 Same location as 17, interm
Page 59 and 60: Site 20 Adjacent to previous site C
Page 61 and 62: Site 22 2 km east of Finnegans brid
Page 64 and 65:
APPENDIX 7: Analytical Results Appe
Page 66 and 67:
Appendix 7.2: Lindsay-Wallpolla Las
Page 68 and 69:
Appendix 7.3: Lindsay-Wallpolla XRF
Page 70 and 71:
16 200709 1929587 20-30 Fm1 7 0.611
Page 72 and 73:
Site Number Depth LEME ID Sample #
show all

GEOMORPHOLOGY REPORT - CRC LEME

Create successful ePaper yourself

Delete template?

Save as template?