Smithfield West Overland Flood Study
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Smithfield West Overland Flood Study Final Report VOLUME 1: Report and Appendices Revision 3 March 2016 Smithfield West Overland Flood Study Final Report REVISION / REVIEW HISTORY Revision # Description Prepared by Reviewed by 1 Draft report for Council / OEH review D. Tetley C. Ryan Final draft report addressing Council 2 D. Tetley C. Ryan comments Final report incorporating outcomes of 3 D. Tetley C. Ryan public exhibition DISTRIBUTION Revision # Distribution List Date Issued Number of Copies 1 Fairfield City Council 13/05/2015 PDF 2 Fairfield City Council 30/06/2015 PDF 3 Fairfield City Council 18/03/2016 PDF Catchment Simulation Solutions Suite 2.01 210 George Street Sydney, NSW, 2000 (02) 9247 4882 [email protected] (02) 8415 7118 www.csse.com.au File Reference: Smithfield West Flood Study (Revision 2) - Volume 1 Report Text.docx The information within this document is and shall remain the property of Catchment Simulation Solutions. i FOREWORD The NSW State Government’s Flood Prone Land Policy is directed towards providing solutions to existing flooding problems in developed areas and ensuring that new development is compatible with the flood hazard and does not create additional flooding problems in other areas. The Policy is defined in the NSW Government’s ‘Floodplain Development Manual’ (NSW Government, 2005). Under the Policy, the management of flood liable land remains the responsibility of Local Government. The State Government subsidises flood mitigation works to alleviate existing problems and provides specialist technical advice to assist Local Government in its floodplain management responsibilities. The Policy provides for technical and financial support by the State Government through the following stages: Floodplain Established by the Risk local council, must Management include community Committee groups and state agency specialists Floodplain Floodplain Implementation Data Flood Risk Risk of Collection Study Management Management Plan Study Plan Defines the nature and Determines options in Preferred options Flood, response and Compilation of existing publicly exhibited and data and collection of extent of the flood consideration of property modification subject to revision in additional data. problem, in technical social, ecological and measures including light of responses. Usually undertaken by rather than map form. economic factors mitigation works, planning Formally approved by consultants appointed Usually undertaken by relating to flood risk. controls, flood warnings, consultants appointed Usually undertaken by the council after public flood readiness and by the council. exhibition and any by the council. consultants appointed response plans, by the council. necessary revisions environmental rehabilitation, due to public ongoing data collection and comments. monitoring. The Smithfield West Overland Flood Study represents stages one and two of the five stage process outlined above. The aim of the Flood Study is to produce information on flood discharges, levels, depths and velocities, for a range of flood events under existing topographic and development conditions. This information can then be used as a basis for identifying those areas where the greatest flood damage is likely to occur, thereby allowing a targeted assessment of where flood mitigation measures would be best implemented as part of the subsequent Floodplain Risk Management Study and Plan. ii TABLE OF CONTENTS 1 INTRODUCTION ......................................................................................................... 1 1.1 Catchment Description...................................................................................... 1 1.2 Purpose of Study ............................................................................................... 1 2 METHODOLOGY ........................................................................................................ 2 2.1 Objectives ........................................................................................................... 2 2.2 Adopted Approach ............................................................................................. 2 3 DATA COLLECTION AND REVIEW ........................................................................ 4 3.1 Overview ............................................................................................................. 4 3.2 Catchment History ............................................................................................. 4 3.2.1 Development History .................................................................................. 4 3.2.2 Flood History ................................................................................................ 5 3.2.3 Mitigation History ......................................................................................... 5 3.3 Previous Reports ............................................................................................... 7 3.3.1 Smithfield West Drainage Study: Chifley Street to The Horsley Drive (1996) ................................................................................................. 7 3.3.2 Prospect Creek Floodplain Management Plan - Flood Study Review (2006) .............................................................................................. 8 3.3.3 Draft Review of Stormwater Flooding Problems – Moir Street to Victoria Street, Smithfield (2012) .............................................................. 9 3.3.4 Overland Flood Studies ............................................................................ 10 3.4 Hydrologic Data ................................................................................................ 11 3.4.1 Historic Rainfall Data ................................................................................ 11 3.4.2 Historic Stream Gauge Data ................................................................... 11 3.5 Topographic and Survey Information ........................................................... 11 3.5.1 Light Detection and Ranging (LiDAR) Survey ...................................... 11 3.5.2 2010 Stormwater Survey ......................................................................... 13 3.5.3 2014 Cross-Section and Stormwater Survey ....................................... 14 3.5.4 Flood Mark Survey .................................................................................... 14 3.6 GIS Data ............................................................................................................ 14 3.7 Flood Photographs .......................................................................................... 16 iii Smithfield West Overland Flood Study 3.8 Community Consultation ................................................................................ 19 3.8.1 General ....................................................................................................... 19 3.8.2 Flood Study Website ................................................................................ 19 3.8.3 Community Information Brochure and Questionnaire ......................... 20 4 COMPUTER FLOOD MODEL ................................................................................. 26 4.1 General .............................................................................................................. 26 4.2 Model Development ........................................................................................ 26 4.2.1 2D Model Extent and Grid Size .............................................................. 26 4.2.2 1D Domain ................................................................................................. 27 4.2.3 Material Types ........................................................................................... 27 4.2.4 Rainfall Losses .......................................................................................... 27 4.2.5 Manning’s ‘n’ Roughness Coefficients ................................................... 28 4.2.6 Building Representation ........................................................................... 30 4.2.7 Stormwater System................................................................................... 31 4.2.8 Fences ........................................................................................................ 33 5 COMPUTER MODEL CALIBRATION .................................................................... 37 5.1 Overview ........................................................................................................... 37 5.2 February 1990 Flood ....................................................................................... 37 5.2.1 Local Catchment Rainfall ......................................................................... 37 5.2.2 Downstream Boundary Conditions ......................................................... 38 5.2.3 Modifications to Represent Historic Conditions .................................... 39 5.2.4 Antecedent Catchment Conditions ......................................................... 39 5.2.5 Results ........................................................................................................ 39 5.3 April 2012 Flood ............................................................................................... 41 5.3.1 Local Catchment Rainfall ......................................................................... 41 5.3.2 Downstream Boundary Conditions ......................................................... 42 5.3.3