Georges River Floodplain Risk Management Study & Plan
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Prepared for the Georges River Floodplain Management Committee GEORGES RIVER FLOODPLAIN RISK MANAGEMENT STUDY & PLAN Volume 1 – Main Report Final Report May 2004 Bewsher Consulting Pty Ltd GEORGES RIVER FLOODPLAIN MANAGEMENT COMMITTEE Comprising Liverpool City Council, Fairfield City Council, Bankstown City Council, Sutherland Shire Council, State Emergency Service, Department of Infrastructure, Planning and Natural Resources, and community representatives. GEORGES RIVER FLOODPLAIN RISK MANAGEMENT STUDY & PLAN Volume 1 – Main Report FINAL REPORT May 2004 Prepared by: BEWSHER CONSULTING PTY LTD P O BOX 352 EPPING NSW 1710 Telephone (02) 9868 1966 Facsimile (02) 9868 5759 Email [email protected] ACN 003137068 GEORGES RIVER FLOODPLAIN RISK MANAGEMENT STUDY BEWSHER CONSULTING PTY LTD May 19, 2004 J1046-Study-V1.doc TABLE OF CONTENTS Page _____________________________________________________________________________________________________ EXECUTIVE SUMMARY 1 1. INTRODUCTION 6 1.1 BACKGROUND 6 1.2 THE STUDY AREA 7 1.3 THE GOVERNMENT’S FLOODPLAIN MANAGEMENT PROCESS 8 1.4 REPORTING 9 2. BACKGROUND INFORMATION 10 2.1 THE GEORGES RIVER CATCHMENT 10 2.2 HISTORY OF FLOODING 14 2.3 PREVIOUS FLOOD INVESTIGATIONS 20 3. COMMUNITY CONSULTATION 26 3.1 CONSULTATION PROCESS 26 3.2 GEORGES RIVER FLOODPLAIN MANAGEMENT COMMITTEE 26 3.3 PROJECT WEB SITE 27 3.4 SES FLOODSAFE BROCHURE 27 3.5 COMMUNITY NOTIFICATION PACK 27 3.6 SHORT QUESTIONNAIRE 28 3.7 DETAILED QUESTIONNAIRE 29 3.8 PUBLIC WORKSHOPS 34 3.9 LIAISON WITH GOVERNMENT AGENCIES AND GROUPS 34 3.10 PUBLIC EXHIBITION OF DRAFT REPORTS 41 4. MODELLING OF FLOOD BEHAVIOUR 42 4.1 PURPOSE 42 4.2 GEORGES RIVER MIKE-11 MODEL 42 4.3 MODEL CALIBRATION 43 4.4 IMPACTS OF RECENT DEVELOPMENT 47 4.5 DESIGN FLOOD LEVELS IN THE LOWER GEORGES RIVER 55 5. DESCRIPTION OF FLOOD BEHAVIOUR 60 5.1 SOURCES OF FLOOD DATA 60 5.2 SUMMARY OF PROPERTY INUNDATION 60 5.3 FLOOD RISK MAPPING 65 5.4 THE PROBABLE MAXIMUM FLOOD 67 5.5 ROAD INUNDATION PROBLEMS 69 5.6 OTHER FLOODING CHARACTERISTICS 70 6. FLOOD DAMAGES ASSESSMENT 76 6.1 FLOOD DAMAGES DATABASE 76 6.2 TYPES OF FLOOD DAMAGE 78 6.3 BASIS OF FLOOD DAMAGE CALCULATIONS 79 6.4 SUMMARY OF FLOOD DAMAGES 79 GEORGES RIVER FLOODPLAIN RISK MANAGEMENT STUDY i BEWSHER CONSULTING PTY LTD May 19, 2004 J1046-Study-V1.doc TABLE OF CONTENTS (cont) Page ___________________________________________________________________ 7. FLOODPLAIN MANAGEMENT CONSIDERATIONS 82 7.1 SELECTION OF THE FLOOD PLANNING LEVELS 82 7.2 TYPES OF FLOODPLAIN MANAGEMENT MEASURES 83 7.3 SUMMARY OF MEASURES CONSIDERED 84 8. REVIEW OF EXISTING FLOODPLAIN MANAGEMENT MEASURES 85 8.1 LIVERPOOL VOLUNTARY PURCHASE SCHEME 85 8.2 BANKSTOWN VOLUNTARY PURCHASE SCHEME 87 8.3 MILPERRA DRAIN CHANNEL AUGMENTATION 89 8.4 KELSO LEVEE 89 8.5 EAST HILLS FINGER LEVEES 91 8.6 CARINYA ROAD FINGER LEVEES 93 9. OTHER POTENTIAL FLOODPLAIN MANAGEMENT MEASURES 94 9.1 FLOOD MITIGATION DAM IN THE UPPER CATCHMENT 94 9.2 RIVER DREDGING 97 9.3 LEVEE AT MILPERRA 99 9.4 STORMWATER CONSIDERATIONS 101 9.5 ADDITIONAL INVESTIGATIONS 102 9.6 COMPENSATORY DEVELOPMENT MEASURES 103 9.7 PLANNING AND DEVELOPMENT CONTROLS 103 9.8 FLOOD WARNING ENHANCEMENTS 107 9.9 EMERGENCY MANAGEMENT OPERATIONS 108 9.10 PUBLIC AWARENESS 109 10. DRAFT FLOODPLAIN RISK MANAGEMENT PLAN 112 10.1 THE RECOMMENDED MEASURES 112 10.2 FUNDING AND IMPLEMENTATION 114 10.3 ON-GOING REVIEW OF PLAN 115 11. ACKNOWLEDGEMENTS 118 12. REFERENCES 119 13. GLOSSARY 122 APPENDICES Appendix A - Consultation Material Appendix B - Frequently Asked Questions Appendix C - Summary of Submissions Received from the Public Exhibition Appendix D - Flood Level Contours from the 1991 Georges River Flood Study GEORGES RIVER FLOODPLAIN RISK MANAGEMENT STUDY ii BEWSHER CONSULTING PTY LTD May 19, 2004 J1046-Study-V1.doc LIST OF TABLES Page ___________________________________________________________________ Table 2.1 – Historical Flood Records 16 Table 3.1 – Short Questionnaire Response Rate 28 Table 3.2 – Short Questionnaire Results 29 Table 3.3 – Measures Most Favoured by the Community 31 Table 3.4 – Measures Least Favoured by the Community 31 Table 3.5 – Consultation with Agencies, Authorities and Groups 36 Table 4.1 – Impact of Filling at Airport on Georges River Flood Levels 49 Table 4.2 – Impact of the Moorebank/Milperra Floodway Scheme 50 Table 4.3 – Impact of M5 Motorway Bridge and Access Track 52 Table 4.4 – Impact of East Hills Flood Mitigation Works 53 Table 4.5 – Impact of Carinya Road Flood Mitigation Works 54 Table 4.6 – Cumulative Impact of Development and Works 55 Table 4.7 – Recommended Storm Tide Levels in Botany Bay 56 Table 5.1 – Residential Property Affected by Flooding 61 Table 5.2 – Commercial/Industrial Property Affected by Flooding 61 Table 5.3 – Inundation Depths for Homes in the 100 Year Flood 63 Table 5.4 – Inundation Depths for Buildings in the 100 Year Flood 63 Table 5.5 – Number of Properties in each Flood Risk Area 64 Table 5.6 – Flooding Characteristics at Liverpool Weir 71 Table 5.7 – Flooding Characteristics at Milperra Bridge 71 Table 6.1 – Properties Included in the Database 76 Table 6.2 – Predicted Flood Damages under Existing Conditions 81 Table 7.1 – Potential Floodplain Management Measures 84 Table 9.1 – Summary of Dam Characteristics and Flood Benefits 95 Table 9.2 – Impact of Dredging on Flood Behaviour 98 Table 9.3 – Impact of Milperra Levee on Flood Behaviour 100 Table 10.1 – Recommended Floodplain Management Measures 116 GEORGES RIVER FLOODPLAIN RISK MANAGEMENT STUDY iii BEWSHER CONSULTING PTY LTD May 19, 2004 J1046-Study-V1.doc LIST OF FIGURES ___________________________________________________________________ Figure 1.1 – The Floodplain Management Process 8 Figure 2.1 – The Georges River Catchment 12 Figure 2.2 – The Georges River Study Area 13 Figure 2.3 – Historical Flood Heights at Liverpool and Lansdowne Bridge 17 Figure 3.1 – Community Views on Floodplain Management Measures 32 Figure 4.1 – MIKE-11 Model Layout – Sheet 1 of 2 44 Figure 4.2 – MIKE-11 Model Layout – Sheet 2 of 2 45 Figure 4.3 – Verification of the Georges River MIKE-11 Model 46 Figure 4.4 – 20 year Flood Levels in the Lower Georges River 57 Figure 4.5 – 100 year Flood Levels in the Lower Georges River 58 Figure 4.6 – PMF Flood Levels in the Lower Georges River 59 Figure 5.1 – Flood Risk Management Precincts 66 Figure 5.2 – Road Inundation Problem Areas 72 Figure 5.3 – Road Inundation Centreline Profiles (Sheet 1 of 2) 73 Figure 5.4 – Road Inundation Centreline Profiles (Sheet 2 of 2) 74 Figure 5.5 – Flood Hydrographs at Liverpool and Milperra 75 Figure 6.1 – Types of Flood Damage 78 Figure 6.2 – Components of Flood Damage for the Georges River 81 Figure 8.1 – Moorebank-Milperra Voluntary Purchase Scheme 88 Figure 9.1 – Potential Flood Mitigation Dam in the Upper Catchment 96 Figure 9.2 – Planning Matrix – Georges River Floodplain 105 Figure 9.3 – Planning Matrix – All other Floodplains 106 Figure 9.4 – Sample Flood Certificate 111 Figure 10.1 – Recommended Floodplain Risk Management Plan 117 LIST OF PHOTOS ___________________________________________________________________ PHOTO 1 – Rescue during 1956 flood, Newbridge Road at Moorebank 18 PHOTO 2 – 1964 flood near East Hills Footbridge 18 PHOTO 3 – 1986 flood, looking upstream to Milperra Bridge 19 PHOTO 4 – 1986 flood, on the lower reaches of Prospect Creek 19 PHOTO 5 – The Range in Flood Levels for Many Houses in Moorebank 68 PHOTO 6 – Chipping Norton in the 1986 Flood 68 GEORGES RIVER FLOODPLAIN RISK MANAGEMENT STUDY iv BEWSHER CONSULTING PTY LTD May 19, 2004 J1046-Study-V1.doc EXECUTIVE SUMMARY Reasons for the Study and Plan The Georges River is one of the most populated catchments in Australia. The river and its tributary creeks represent Sydney’s most immediate flood problem, both in terms of the number of properties affected by flooding and the potential for increased flood damage due to development pressures within the catchment. Bewsher Consulting was commissioned by Bankstown City Council and Liverpool City Council in June 2001 to develop a floodplain risk management study and plan for the Georges River. The study was later expanded to incorporate parts of Fairfield City Council and Sutherland Shire Council. Numerous flood investigations have been undertaken on the Georges River over the years. Most have focused on specific problem areas along the river, and in many cases flood mitigation schemes have been developed to tackle these problems. Many of the schemes have since been implemented, or are in the process of being implemented. Whilst there has been substantial progress in reducing the extent of flooding problems along the river, there remains a significant flood risk to many properties. There has also been no overall strategic floodplain risk management study that considers the broader catchment-wide measures, such as flood warning, emergency management measures, public awareness and consistent planning controls for future development. The Study report has been produced in two volumes – a main report (Volume 1) and a supplementary report covering planning issues (Volume 2), given the critical importance of the latter to floodplain management on the Georges River. Responsibilities The prime responsibility for planning and management of flood prone lands in NSW rests with local government. The NSW Government provides assistance on state- wide policy issues and technical support. Financial assistance is also provided to undertake flood and floodplain risk management studies and for the implementation of works identified in any subsequent floodplain risk management plan. The Georges River Floodplain Management Committee oversaw the Study. This committee includes Councillors and staff from Bankstown, Liverpool, Fairfield and Sutherland Shire Councils. Officers form the Department of Land and Water Conservation (now the Department of Infrastructure, Planning and Natural Resources) and the State Emergency Service were also represented on the committee, along with a number of community representatives.