UPPER LACHLAN SHIRE COUNCIL THE VILLAGES OF CROOKWELL, GUNNING, COLLECTOR AND TARALGA FLOODPLAIN RISK MANAGEMENT STUDY AND DRAFT PLAN NOVEMBER 2016 VOLUME 1 – REPORT DRAFT REPORT FOR PUBLIC EXHIBITION Job No: DN374 Date: November 2016 Principals: SAB File: FVFRMS_V1_Report_[Rev 1.2].doc Rev No: 1.2 Authors: SAB/TDR The Villages of Crookwell, Gunning, Collector and Taralga Floodplain Risk Management Study and Draft Plan FOREWORD NSW Government’s Flood Policy The NSW Government’s Flood Policy is directed at providing solutions to existing flooding problems in developed areas and to ensuring that new development is compatible with the flood hazard and does not create additional flooding problems in other areas. Under the Policy, the management of flood liable land remains the responsibility of local government. The State subsidises flood mitigation works to alleviate existing problems and provides specialist technical advice to assist councils in the discharge of their floodplain management responsibilities. The Policy provides for technical and financial support by the State through the following four sequential stages: 1. Data Collection and Flood Study Collects flood related data and undertakes an investigation to determine the nature and extent of flooding. 2. Floodplain Risk Management Study Evaluates management options for the floodplain in respect of both existing and proposed development. 3. Floodplain Risk Management Plan Involves formal adoption by Council of a plan of management for the floodplain. 4. Implementation of the Plan Construction of flood mitigation works to protect existing development. Use of Local Environmental Plans to ensure new development is compatible with the flood hazard. Presentation of Study Results The results of the flood study investigations commissioned by Upper Lachlan Shire Council have been presented in five separate reports: Data Collection Report, November, 2012. Four Flood Study Reports (herein, collectively referred to as the Flood Studies), one for each of the four villages of Crookwell, Gunning, Collector and Taralga all dated February 2014 and adopted by Council on 19 December 2013. Floodplain Risk Management Study & Plan (this present report) The studies have been prepared under the guidance of the Floodplain Management Committee comprising representatives from Upper Lachlan Shire Council, the Office of Environment and Heritage and the NSW State Emergency Service. ACKNOWLEDGEMENT The studies have been prepared with financial assistance from the NSW Government’s Floodplain Management Program and the technical support of Office of Environment and Heritage. This document does not necessarily represent the opinions of the NSW Government. FVFRMS_V1_Report_[Rev 1.2].doc i Lyall & Associates November 2016 Rev. 1.2 The Villages of Crookwell, Gunning, Collector and Taralga Floodplain Risk Management Study and Draft Plan TABLE OF CONTENTS Page No. SUMMARY ............................................................................................................................... S1 1 INTRODUCTION ............................................................................................................ 1 1.1 Study Background .............................................................................................. 1 1.2 Background Information ...................................................................................... 1 1.3 Overview of FRMS Report .................................................................................. 1 1.4 Community Consultation ..................................................................................... 3 1.5 Flood Frequency and Terminology ...................................................................... 3 2 BASELINE FLOODING CONDITIONS ........................................................................... 4 2.1 Physical Setting .................................................................................................. 4 2.2 Drainage System ................................................................................................ 5 2.3 Recent Flood Experience .................................................................................... 6 2.4 Design Flood Behaviour ..................................................................................... 8 2.4.1 Background ............................................................................................ 8 2.4.2 Recent Updates to the Flood Models ...................................................... 8 2.4.3 Design Flooding Patterns ....................................................................... 9 2.5 Impact of Flooding on Critical Infrastructure ...................................................... 11 2.6 Flood Hazard and Hydraulic Categorisation of the Floodplain ........................... 14 2.6.1 General ................................................................................................ 14 2.6.2 Flood Hazard Categorisation ................................................................ 14 2.6.3 Hydraulic Categorisation of the Floodplain ............................................ 15 2.7 Recommended Sub Division of the Floodplain .................................................. 18 2.8 Council’s Existing Planning Instruments and Policies ........................................ 20 2.8.1 General ................................................................................................ 20 2.8.2 Land Use Zoning – Upper Lachlan Local Environment Plan 2010 ......... 20 2.8.3 Flood Provisions – Upper Lachlan LEP 2010 ........................................ 21 2.8.4 Flooding and Stormwater Controls – Upper Lachlan DCP 2010 ............ 22 2.9 Potential Impacts of Future Urbanisation .......................................................... 24 2.10 Potential Impacts of Climate Change ................................................................ 24 2.11 Impacts of a Potential Dam Failure on Flooding Behaviour ............................... 26 2.11.1 General ................................................................................................ 26 2.11.2 Methods of Analysis ............................................................................. 27 2.11.3 Results of Dam Break Analysis ............................................................. 28 2.11.4 Dam Classification and Future Refinements to the Dam Break Analysis 29 2.12 Economic Impacts of Flooding .......................................................................... 30 2.13 Flood Warning and Flood Preparedness ........................................................... 33 2.14 Environmental Considerations .......................................................................... 33 3 POTENTIAL FLOODPLAIN MANAGEMENT MEASURES ........................................... 34 3.1 Range of Available Measures ........................................................................... 34 3.2 Community Views ............................................................................................. 34 3.3 Outline of Chapter ............................................................................................ 36 3.4 Flood Modification Measures ............................................................................ 36 Cont'd Over FVFRMS_V1_Report_[Rev 1.2].doc ii Lyall & Associates November 2016 Rev. 1.2 The Villages of Crookwell, Gunning, Collector and Taralga Floodplain Risk Management Study and Draft Plan TABLE OF CONTENTS (Cont'd) Page No. 3.5 Property Modification Measures ........................................................................ 38 3.5.1 Controls over Future Development ....................................................... 38 3.5.2 Voluntary Purchase of Residential Properties ....................................... 43 3.5.3 Raising Floor Levels of Residential Properties ...................................... 45 3.6 Response Modification Measures ..................................................................... 46 3.6.1 Improvements to Flood Warning System ............................................... 46 3.6.2 Improved Emergency Planning and Response ...................................... 49 3.6.3 Public Awareness Programs ................................................................. 53 3.6.4 Dam Safety Emergency Plans .............................................................. 54 3.7 Summary .......................................................................................................... 55 4 SELECTION OF FLOODPLAIN MANAGEMENT MEASURES ..................................... 59 4.1 Background ...................................................................................................... 59 4.2 Ranking of Options ........................................................................................... 59 4.3 Summary .......................................................................................................... 60 5 DRAFT FLOODPLAIN RISK MANAGEMENT PLAN .................................................... 66 5.1 The Floodplain Risk Management Process ....................................................... 66 5.2 Purpose of the Plan .......................................................................................... 66 5.3 The Study Area ................................................................................................ 66 5.4 Community Consultation ................................................................................... 66 5.5 Economic Impacts