SOUTH CREEK FLOODPLAIN RISK MANAGEMENT STUDY AND PLAN For the Liverpool Local Government Area Cover Photo: South Creek between Elizabeth Drive and Overett Avenue, Kemps Creek Final Report VOLUME 1 — STUDY REPORT AND RECOMMENDED PLAN December 2004 Bewsher Consulting Pty Ltd LIVERPOOL CITY COUNCIL SOUTH CREEK FLOODPLAIN RISK MANAGEMENT STUDY AND PLAN FOR THE LIVERPOOL LOCAL GOVERNMENT AREA FINAL REPORT VOLUME 1 — STUDY REPORT AND RECOMMENDED PLAN DECEMBER 2004 Prepared by: BEWSHER CONSULTING PTY LTD P O BOX 352 EPPING NSW 1710 Telephone (02) 9868 1966 Facsimile (02) 9868 5759 E-mail: [email protected] ACN 003 137 068 ABN 24 312 540 210 SOUTH CREEK FLOODPLAIN RISK MANAGEMENT STUDY BEWSHER CONSULTING PTY LTD FOR LIVERPOOL LGA — FINAL REPORT December 2004 J1184-FinalReport-Dec04.doc FOREWORD In New South Wales, the prime responsibility for local planning and the management of flood liable land rests with local government. To assist local government with floodplain management, the NSW Government has adopted a Flood Prone Land Policy in conjunction with the Floodplain Management Manual. The Policy is directed at providing solutions to existing flood problems and to ensure that new development is compatible with the flood hazard and does not create additional flood problems. The Policy sets out four sequential stages in the development of a floodplain management system: 1. Flood Study — Assessment to define the nature and extent of flooding. 2. Floodplain Risk Management Study — Comprehensive evaluation of management options with respect to existing and proposed development. 3. Floodplain Risk Management Plan — Formal adoption by Council of a management plan for floodplain risks. 4. Implementation of the Plan — Measures undertaken to reduce the impact of flooding on existing development, and implementing controls to ensure that new development is compatible with the flood hazard. This Floodplain Risk Management Study and recommended Floodplain Risk Management Plan constitutes the second and third stages of the management process for the South Creek study area within the Liverpool Local Government Area, and has been prepared for Liverpool City Council by Bewsher Consulting Pty Ltd in association with Don Fox Planning Pty Ltd. In broad terms, this Floodplain Risk Management Study has investigated what can be done to minimise the effects of flooding in the South Creek study area, and has recommended a strategy in the form of a recommended Floodplain Risk Management Plan. This Floodplain Risk Management Study has been prepared in two volumes: 4 Volume 1 — Main Report (this report), which includes the Executive Summary, the Floodplain Risk Management Study, recommended Floodplain Risk Management Plan and the Appendices; 4 Volume 2 — Town Planning Issues, which includes a review of planning and development controls for the study area, together with a draft Flood Risk Management Development Control Plan for the Liverpool Local Government Area and Planning Matrix of planning and development controls for the South Creek study area. A Flood Damages Data Base of potentially flood-affected properties has been supplied separately to Council (see Section 3.5). The next stage of the floodplain risk management process will be for Liverpool City Council to formally adopt the recommended Floodplain Risk Management Plan. SOUTH CREEK FLOODPLAIN RISK MANAGEMENT STUDY BEWSHER CONSULTING PTY LTD FOR LIVERPOOL LGA — FINAL REPORT December 2004 J1184-FinalReport-Dec04.doc VOLUME 1 — STUDY REPORT AND RECOMMENDED PLAN TABLE OF CONTENTS Page EXECUTIVE SUMMARY ................................................................................................................... ES-1 1. INTRODUCTION............................................................................................................................. 1 1.1 STUDY AREA........................................................................................................................... 4 1.1.1 Creeks and Floodplains.................................................................................................. 4 1.1.2 Topography .................................................................................................................... 6 1.1.3 Vegetation ...................................................................................................................... 6 1.1.4 Land Use and Population ............................................................................................... 7 1.1.5 South West Urban Release Investigation Area .............................................................. 8 1.2 STUDY OBJECTIVES .............................................................................................................. 8 1.3 THE NSW GOVERNMENT'S FLOODPLAIN RISK MANAGEMENT PROCESS .................... 9 1.4 FUNDING OF FLOODPLAIN RISK MANAGEMENT PLAN................................................... 11 1.5 ROLES AND RESPONSIBILITIES OF ORGANISATIONS.................................................... 11 2. FLOOD BEHAVIOUR ................................................................................................................... 13 2.1 FLOOD HISTORY .................................................................................................................. 13 2.1.1 River Gauging Stations................................................................................................. 13 2.1.2 Major Floods of the 1980s............................................................................................ 14 2.1.3 Top Ten Floods in South Creek at Elizabeth Drive — 1955 to 1988............................ 14 2.2 HYDROLOGIC MODELLING ................................................................................................. 16 2.2.1 Hydrologic Modelling From Previous Studies............................................................... 16 1990 Flood Study Report for South Creek .............................................................. 16 1991 South Creek Floodplain Management Study.................................................. 20 1994–1997 Flood Mitigation Studies for the Overett and Victor Avenue Areas ...... 20 2.2.2 Design Flows for South Creek for Current Study ......................................................... 21 2.3 HYDRAULIC MODELLING..................................................................................................... 21 2.3.1 Hydraulic Modelling from Previous Studies .................................................................. 22 Calibration of the South Creek MIKE-11 Model ...................................................... 22 Calculation of the Hydraulic Floodway for South Creek .......................................... 22 Evolution of MIKE-11 Modelling .............................................................................. 22 Design Flood Levels from Previous Studies............................................................ 23 2.3.2 Establishment of the 2003 MIKE-11 model .................................................................. 23 Utilising Previous MIKE-11 Models for the Current Study....................................... 23 Utilising the Existing Thompsons Creek HEC-2 Model ........................................... 23 The 2003 South Creek MIKE-11 model .................................................................. 24 2.3.3 Design Flood Levels For South Creek For Current Study............................................ 24 3. AVAILABLE MAPPING, SURVEY AND BASE INFORMATION.................................................. 28 3.1 INFORMATION FROM LIVERPOOL CITY COUNCIL GIS.................................................... 28 3.2 AVAILABLE GROUND SURVEY IN THE STUDY AREA....................................................... 28 3.2.1 Ground Survey of South Creek Floodplain Area .......................................................... 29 3.2.2 Cross-sections for Hydraulic Modelling of South Creek and Thompsons Creek ......... 31 3.2.3 Floor Levels of Properties in the Floodplain ................................................................. 31 3.3 DIGITAL TERRAIN MODEL ESTABLISHED FOR THIS STUDY .......................................... 32 3.4 OTHER TOPOGRAPHICAL INFORMATION......................................................................... 34 3.5 FLOOD DAMAGES DATA BASE ........................................................................................... 35 4. IMPACTS AND COSTS OF FLOODING ...................................................................................... 38 4.1 MAPPING OF DESIGN FLOOD EVENTS.............................................................................. 38 4.2 MAPPING OF FLOOD RISK PRECINCTS............................................................................. 43 4.2.1 Flood Hazard Categories.............................................................................................. 43 4.2.2 Flood Hydraulic Categories .......................................................................................... 44 4.2.3 Flood Risk Precincts for the South Creek Study Area.................................................. 47 SOUTH CREEK FLOODPLAIN RISK MANAGEMENT STUDY i BEWSHER CONSULTING PTY LTD FOR LIVERPOOL LGA — FINAL REPORT December 2004 J1184-FinalReport-Dec04.doc TABLE OF CONTENTS (continued) Page 4.3 PROPERTIES AFFECTED BY FLOODING........................................................................... 49 4.4 FLOOD RISK CATEGORISATION OF PROPERTIES .........................................................