A part of BMT in Energy and Environment Casterton Flood Intelligence & Warning Improvements Reference: R.M8575.003.01.Final Date: 15 January 2014 Confidential Casterton Flood Intelligence & Warning Improvements Prepared for: Glenelg Hopkins Catchment Management Authority Prepared by: BMT WBM Pty Ltd (Member of the BMT group of companies) Offices Brisbane Denver London Mackay Melbourne Newcastle Perth Sydney Vancouver T:\M8575.MAJ.Casteron_FI\docs\R.M8575.003.01.Final.docx Document Control Sheet Document: R.M8575.003.01.Final BMT WBM Pty Ltd Level 5, 99 King Street Title: Casterton Flood Intelligence & Warning Melbourne Vic 3000 Improvements Australia PO Box 604 Project Manager: Philip Pedruco Collins Street West Vic 8007 Author: Tel: +61 3 8620 6100 Fax: +61 3 8620 6105 Client: Glenelg Hopkins Catchment Management Authority ABN 54 010 830 421 Client Contact: Jacinta Herrmann www.bmtwbm.com.au Client Reference: Philip Pedruco Synopsis: This report documents the findings and results of the Casterton Flood Intelligence and Warning Improvements REVISION/CHECKING HISTORY Revision Number Date Checked by Issued by 0 19/11/2013 MT PP 1 14/1/2014 MT PP DISTRIBUTION Destination Revision 0 1 2 3 4 5 6 7 8 9 10 GHCMA (hard copy) 1 GHCMA (pdf) 1 1 BMT WBM File 1 1 BMT WBM Library 1 T:\M8575.MAJ.Casteron_FI\docs\R.M8575.003.01.Final.docx Casterton Flood Intelligence & Warning Improvements i Contents Contents 1 Introduction 1 1.1 Background (incl. History and Catchment details) 1 1.2 Previous Studies 1 1.3 Aims and Objectives 2 1.4 Report Outline 2 2 Data Collection 4 2.1 Data 4 3 Data Review and Analysis 6 3.1 Adjustments to data 6 3.1.1 LiDAR Data 6 3.1.2 Casterton Gauge Heights 6 3.2 Regression Relationships 6 3.2.1 Dergholm Gauge Heights 7 3.2.2 Wando Vale to Casterton 8 3.2.3 Dergholm to Casterton 10 4 Existing Flood Warning System 13 5 Flood Modelling 14 5.1 Hydrology 14 5.1.1 Flood Frequency Analysis 14 5.1.2 Rainfall-Runoff Modelling 15 5.1.3 Wannon River Inflow 18 5.1.3.1 Flood Frequency Analysis 18 5.1.3.2 Representative Hydrograph 19 5.1.3.3 Probable Maximum Flood 20 5.2 Hydraulics 20 5.2.1 Model Schematisation 20 5.2.2 TUFLOW Version 21 5.2.3 Event Modelling 21 5.2.4 Model Extent 23 5.2.5 2D Domain 23 5.2.5.1 2D Hydraulic Structures 23 5.2.5.2 Surface Roughness 23 5.2.6 1D Network 23 5.2.7 Boundary Conditions 23 T:\M8575.MAJ.Casteron_FI\docs\R.M8575.003.01.Final.docx Casterton Flood Intelligence & Warning Improvements ii Contents 5.3 Flood Mapping 26 5.3.1 Description of flooding 26 5.3.1.1 20% AEP event 26 5.3.1.2 10% AEP event 26 5.3.1.3 5% AEP event 26 5.3.1.4 2% AEP event 27 5.3.1.5 1% AEP event 27 5.3.1.6 The PMF event 27 5.3.2 Comparison with previous flood mapping 34 5.4 Influence of the Wannon River 40 6 Flood Information 45 6.1 Casterton Gauge Level 45 6.2 Property Inundation 46 6.3 Road Closures 46 7 Flood Visualisation Tool 48 7.1 Flood Information 48 7.2 Features of the Flood Visualisation Tool 48 7.3 Limitations 49 8 Conclusions and Recommendations 50 8.1 River gauging relationships 50 8.1.1 Updated flood modelling and mapping 50 8.1.2 Review and update of the flood warning system for Casterton 51 8.1.3 Flood Visualisation Tool 51 8.2 Recommendations 51 9 References 52 Appendix A Regression Analysis Diagnostics A-1 A.1 Old and new Dergholm Regression Analysis Diagnostics A-1 A.2 Wando Vale – Casterton Regression Analysis Diagnostics A-3 A.3 Dergholm – Casterton Regression Analysis Diagnostics A-5 Appendix B Flood Warning Service Level Agreement for the Glenelg River at Casterton B-1 Appendix C Flood Forecast and Warning Service Level Agreement for the Glenelg River at Casterton C-1 Appendix D PMP Calculation D-1 Appendix E Property Inundation E-1 T:\M8575.MAJ.Casteron_FI\docs\R.M8575.003.01.Final.docx Casterton Flood Intelligence & Warning Improvements iii Contents List of Figures Figure 1-1 Significant hydrologic features 3 Figure 3-1 Old and New Dergholm Regression Analysis 8 Figure 3-2 Wando Vale Casterton Regression Analysis 10 Figure 3-3 Dergholm Casterton Regression Analysis 12 Figure 5-1 RORB model layout 17 Figure 5-2 Flood Magnitude prediction by FFA 19 Figure 5-3 TUFLOW model layout 25 Figure 5-4 Casterton 20% AEP Peak Flood Depth Map 28 Figure 5-5 Casterton 10% AEP Peak Flood Depth Map 29 Figure 5-6 Casterton 5% AEP Peak Flood Depth Map 30 Figure 5-7 Casterton 2% AEP Peak Flood Depth Map 31 Figure 5-8 Casterton 1% AEP Peak Flood Depth Map 32 Figure 5-9 Casterton PMF Peak Flood Depth Map 33 Figure 5-10 Comparison of previous and revised flood mapping for the 10% AEP event 36 Figure 5-11 Comparison of previous and revised flood mapping for the 5% AEP event 37 Figure 5-12 Comparison of previous and revised flood mapping for the 2% AEP event 38 Figure 5-13 Comparison of previous and revised flood mapping for the 1% AEP event 39 Figure 5-14 Comparison of the 1% AEP hydrographs for Glenelg and Wannon Rivers 40 Figure 5-15 1% AEP Flood Level Long Section in the Glenelg River with various Wannon inflow offsets 41 Figure 5-16 Glenelg River chainages 42 Figure 5-17 Level time plots for various locations on the Glenelg River 43 Figure 5-18 Peak gauge height at Casterton under a number of combination of inflows on the Glenelg and Wannon Rivers 44 Figure 6-1 AEP above floor flooding, property inundation and road closures 47 Figure A-1 Old and New Dergholm Residuals verses Fitted Plot A-2 Figure A-2 Old and New Dergholm Normal Q-Q Plot A-2 Figure A-3 Old and New Dergholm Residuals verses Fitted Leverage Plot A-3 Figure A-4 Wando Vale – Casterton Residuals verses Fitted Plot A-4 Figure A-5 Wando Vale – Casterton Normal Q-Q Plot A-4 Figure A-6 Wando Vale – Casterton Residuals verses Fitted Leverage Plot A-5 Figure A-7 Dergholm – Casterton Residuals verses Fitted Plot A-6 Figure A-8 Dergholm – Casterton Residuals Normal Q-Q Plot A-6 Figure A-9 Dergholm – Casterton Residuals verses Fitted Leverage Plot A-7 T:\M8575.MAJ.Casteron_FI\docs\R.M8575.003.01.Final.docx Casterton Flood Intelligence & Warning Improvements iv Contents List of Tables Table 1-1 Notable Floods in Casterton 1 Table 2-1 Datasets 4 Table 3-1 Changes to Casterton Gauge Heights 6 Table 3-2 Old and New Gauge Heights for the Glenelg River at Casterton 7 Table 3-3 Wando Vale Casterton Peak Height Data 9 Table 3-4 Dergholm Casterton Peak Height Data 11 Table 5-1 Peak flow estimates for the Glenelg River at Casterton 15 Table 5-2 List of durations the hydraulic model was run for 16 Table 5-3 Flood Magnitudes for Different ARI as estimated by the FFA 19 Table 5-4 GSAM Estimate of PMP Rainfall Depth 20 Table 5-5 The PMF peak flows for a variety of durations 20 Table 5-6 List of modelled events 21 Table 6-1 Casterton Gauge Heights for notable events 45 Table A-1 Wando Vale – Casterton Regression model summary A-1 Table A-2 Wando Vale –Casterton Regression model summary A-4 Table A-3 Wando Vale –Casterton Regression model summary A-6 Table E-1 Property Inundation E-2 Table E-2 Above Floor Flooding E-12 T:\M8575.MAJ.Casteron_FI\docs\R.M8575.003.01.Final.docx Casterton Flood Intelligence & Warning Improvements 1 Introduction 1 Introduction The town of Casterton is located in south-western Victoria on the Glenelg River and has a long history of flooding with major flood events in 1906, 1946 and 1983. To improve the understanding of the impact of flooding on the Casterton community the Glenelg Hopkins Catchment Management Authority (GHCMA) commissioned the Casterton Flood Intelligence and Warning Improvements study (the Study). The report documents the findings and conclusions of the Study. 1.1 Background (incl. History and Catchment details) The location of Casterton is shown in Figure 1-1 together with the Glenelg River catchment including major tributaries, river and rainfall gauges and other significant features. The Glenelg River has a catchment area of approximately 12,000km2 at its point of discharge to Bass Strait at Nelson. The catchment headwaters are in the Grampians which drain towards the west to Rockland Reservoir. From Rocklands the Glenelg River generally drains to the west until its confluence with the Chetwynd River upstream of Dergholm. The river then gradually turns to the south east and flows towards Casterton, with the Wando River joining the Glenelg between Dergholm and Casterton. Downstream of Casterton, near Sandford, the Wannon River joins the Glenelg River, which is its largest tributary. From this point the Glenelg River drains in a generally southerly direction until it discharges to Bass Strait. The Casterton Central Business District is located on the right hand bank of the Glenelg River in an incised valley that rises steeply to the east and west of the town. During major flood events water breaks out of the Glenelg River and inundates the town centre from the north.