OURIMBAH CREEK FLOODPLAIN RISK MANAGEMENT STUDY AND PLAN PUBLIC EXHIBITION Chittaway Point June 2007 Public Exhibition Draft March 2019 Level 2, 160 Clarence Street Sydney, NSW, 2000 Tel: 9299 2855 Fax: 9262 6208 Email: [email protected] Web: www.wmawater.com.au OURIMBAH CREEK FLOODPLAIN RISK MANAGEMENT STUDY AND PLAN PUBLIC EXHIBITION MARCH 2019 Project Project Number Ourimbah Creek Floodplain Risk Management Study and Plan 115046 Client Client’s Representative Central Coast Council Peter Sheath / Robert Baker / Vic Tysoe / Phil Foster Authors Prepared by: Zac Richards Richard Dewar Date Verified by 19 March 2019 Revision Description Distribution Date 6 FRMS&P – Public Exhibition V Tysoe 19 March 2019 Public6 FRMS – Public Exhibition Exhibition P. Sheath DraftOctober 2018 5 FRMS – Draft Final P. Sheath, V Tysoe, L Davis December 2017 4 FRMS – Draft Final P. Sheath, R Baker March 2017 3 FRMS – Draft Revision Phil Foster December 2016 2 FRMS – First Draft Phil Foster July 2016 1 FRMS – Progress Report 1 Phil Foster January 2016 OURIMBAH CREEK FLOODPLAIN RISK MANAGEMENT STUDY AND PLAN TABLE OF CONTENTS PAGE FOREWORD ............................................................................................................................... i EXECUTIVE SUMMARY ........................................................................................................... iv 1. OURIMBAH CREEK FLOODPLAIN RISK MANAGEMENT PLAN ............................ 1 1.1. Introduction ................................................................................................. 1 1.2. Risk Management Measures Considered ................................................... 1 1.2.1. Relative Merits of Management Measures .................................................. 5 1.2.2. Management Matrix .................................................................................... 5 1.3. Floodplain Risk Management Measures in Plan ......................................... 9 2. INTRODUCTION ...................................................................................................... 11 2.1. Study Objectives ....................................................................................... 11 2.2. Floodplain Risk Management Study and Plan Objectives ......................... 11 2.3. Brief Specific Objectives ........................................................................... 12 3. BACKGROUND ....................................................................................................... 13 3.1. Summary of Flood Risk and Affectation .................................................... 14 3.2. Relevant Studies ...................................................................................... 15 3.2.1. Previous Studies ....................................................................................... 15 3.2.2. Paterson Consultants - Lower Ourimbah Creek Floodplain Risk Management Study Review and Plan, July 2011 (Reference 3) ............. 16 3.2.3. Webb McKeown & Associates - Bangalow Creek and Cut Rock Creek Floodplain Management Study, May 1997 (Reference 6) ...................... 17 3.2.4. WMAwater - Tuggerah Lakes Floodplain Risk Management Study - Final Report, November 2014 (Reference 4) .................................................. 18 3.2.5. WMAwater – Review of Bangalow Creek and Cut Rock Creek Floodplain Management Plan – Area G2, December 2014 (Reference 10) ............. 18 3.2.6. Jacobs – Upgrade of Pacific Highway HW10, Ourimbah Street to Parsons Road, Lisarow, Roads and Maritime Services, October 2014 (Reference Public 12)Exhibition ................................................................................................ Draft......... 20 3.3. Overview of Existing Catchment ............................................................... 21 3.3.1. Demographic Overview ............................................................................ 21 3.3.2. Land Use .................................................................................................. 22 3.4. Available Data for FRMS&P ...................................................................... 23 3.4.1. Data Request ............................................................................................ 23 3.4.2. Floor Level Survey and Estimation ........................................................... 23 4. STAKEHOLDER CONSULTATION ......................................................................... 25 4.1. Questionnaire Distribution ......................................................................... 25 4.2. Specific Consultation with Key Stakeholders and Agencies ...................... 26 4.2.1. Wyong Council Planners........................................................................... 27 4.2.2. Gosford Council Planners ......................................................................... 28 4.2.3. The University of Newcastle ..................................................................... 29 4.2.4. Local Land Services (LLS) ........................................................................ 29 4.2.5. Manly Hydraulics Lab (MHL) ..................................................................... 29 4.2.6. Roads and Maritime Services (RMS) ........................................................ 30 4.2.7. Transport for NSW .................................................................................... 31 4.2.8. Ourimbah Residents Association .............................................................. 32 4.3. Public Exhibition of the Draft Ourimbah Creek FRMS in March 2017 ........ 33 5. OURIMBAH CREEK FLOOD STUDY SUMMARY ................................................... 34 5.1. Aims and Objectives of the Flood Study ................................................... 34 5.2. Flood Study Review .................................................................................. 34 5.2.1. Hydrology Overview .................................................................................. 34 5.2.2. Sub-Catchment Delineation and Parameters ............................................ 34 5.2.3. Hydrologic Model Calibration/Verification .................................................. 35 5.2.4. Design Rainfall ......................................................................................... 35 5.2.5. Critical Duration Analysis .......................................................................... 36 5.2.6. Design Losses .......................................................................................... 36 5.2.7. Areal Reduction Factor ............................................................................. 37 5.2.8. Hydraulic Modelling Review ...................................................................... 37 5.2.9. Model Extent and Topography .................................................................. 38 5.2.10. Roughness ............................................................................................ 38 5.2.11. Hydraulic Model Calibration/Verification ................................................. 38 5.3. Flood Study Design Event Results ............................................................ 39 Public5.3.1. Peak Exhibition Flows ............................................................................................... Draft 39 5.3.2. Flood Depths and Levels .......................................................................... 41 5.4. Provisional Hydraulic Categories .............................................................. 41 5.5. Provisional Hydraulic Hazard Classification .............................................. 42 5.6. Flood Study Emergency Response Planning Maps .................................. 43 6. EXISTING FLOOD BEHAVIOUR ............................................................................. 46 6.1. Hydraulic Categorisation ........................................................................... 46 6.2. Flood Hazard Classification ...................................................................... 46 6.3. Emergency Response Planning Classifications ........................................ 47 6.4. Road Inundation and Access .................................................................... 47 6.5. Existing Levee Assessment ...................................................................... 50 6.5.1. Tuggerah Business Park Levee ................................................................ 50 6.5.2. Main Northern Railway Line Levee ........................................................... 51 7. ECONOMIC IMPACTS OF FLOODING .................................................................... 53 7.1. Tangible Flood Damages .......................................................................... 54 7.1.1. Residential Properties ............................................................................... 56 7.1.2. Non-Residential – Commercial and Industrial ........................................... 56 7.1.3. Critical Infrastructure and Vulnerable Facilities ......................................... 57 7.2. Intangible Flood Damages ........................................................................ 58 8. CURRENT PLANNING INSTRUMENTS AND LEGISLATION ................................. 60 8.1. National Provisions – Building Code of Australia ...................................... 60 8.2. State Provisions ........................................................................................ 60 8.2.1. EP&A Act 1979 ........................................................................................