Appendix P Drainage, Flooding, Stormwater Management Part 5

More documents

Recommendations

Info

900 800 700 600 500 400 300 200 100 0 Flooding, Drainage and Stormwater Management Sanctuary Villages 30 45 60 90 120 180 270 360 540 720 1080 1440 1800 2160 2880 Storm Duration (min) 1 year Existing Flow 1 year Developed Flow 10 year Existing Flow 10 year Developed Flow 100 year Existing Flow 100 year Developed Flow Figure 5: Comparison of 1, 10 and 100 year ARI storm events for a range of storm durations PARSONS BRINCKERHOFF 2122870A-PR0116 Page 15 Peak Flow Rate (m 3 /s)
Flooding, Drainage and Stormwater Management Sanctuary Villages 4. Hydraulic modelling The HEC-RAS (Version 3.1.2, April 2004) computer model, developed by the Hydrologic Engineering Centre, U.S. Army Corps of Engineers was used to determine the 100 year water profile within Congewai and Quorrobolong Creeks south of the development precincts. The programme uses the standard step method to determine water surface profiles for gradually varied flow. 4.1 Modelling parameters The hydraulic analysis has been undertaken as a steady state simulation. A brief discussion on model parameters is provided below. Storage within Ellalong Lagoon has been accounted for in the hydrologic model described in Section 3. 4.1.1 Flow regime A mixed flow regime analysis was undertaken for the analysed portion of Congewai and Quorrobolong Creeks situated within the study area. 4.1.2 Boundary conditions For mixed flow, both upstream and downstream boundary conditions are required for model simulation. The upstream boundary conditions assumed normal flow with a creek slope of 0.003. The sensitivity of the model to this slope has not been examined but is likely to be negligible given that flow is subcritical. The downstream boundary condition comprised a fixed water level that was obtained from the Wollombi Valley Flood Study prepared by Patterson Britton and Partners. A level of 110.1m AHD, which is situated approximately 150m upstream of Millfield Bridge, was adopted. The sensitivity of the model to this starting level has not been examined. 4.1.3 Peak flows A summary of 100 year ARI peak flow rates used within the hydraulic model are provided in Table 4-1. These flows were taken from the XP-RAFTS model for the 2160 minute critical storm duration. Note that the existing and developed peak flow rate estimates for the critical duration storm event are identical. PARSONS BRINCKERHOFF 2122870A-PR0116 Page 16
Page 1 and 2: Flooding, Drainage and Stormwater M
Page 3 and 4: Flooding, Drainage and Stormwater M
Page 5: Flooding, Drainage and Stormwater M

Appendix P Drainage, Flooding, Stormwater Management Part 5

Create successful ePaper yourself

Delete template?

Save as template?