Flood Hazard Assessment Full Report
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Maunsell Australia Pty Ltd ABN 20 093 846 925 REPORT TOWNSVILLE CITY TOWNSVILLE FLOOD COUNCIL HAZARD ASSESSMENT STUDY Phase 2 Report Volume 1 – Flood Hazard Assessment December 2005 Job No. 80301202.01 AN AECOM COMPANY Townsville Flood Hazard Assessment Study Phase 2 Report Volume 1 – Flood Hazard Assessment Revision Revision Date Details Authorised Name/Position Signature A 08/03/06 Final Issue Brian Wright Original Manager signed by Environment NQ Brian Wright © Maunsell Australia Proprietary Limited 2002 The information contained in this document produced by Maunsell Australia Pty Ltd is solely for the use of the Client identified on the cover sheet for the purpose for which it has been prepared and Maunsell Australia Pty Ltd undertakes no duty to or accepts any responsibility to any third party who may rely upon this document. All rights reserved. No section or element of this document may be removed from this document, reproduced, electronically stored or transmitted in any form without the written permission of Maunsell Australia Pty Ltd. Townsville Flood Hazard Assessment Study Revision A Phase 2 Report – Volume 1 – Flood Study December 2005 J:MMPL\80301202.02\Administration\phase 3\revised final\report.doc Page 2 of 84 Table of Contents Volume 1 – Flood Hazard Assessment Executive Summary 7 1 Introduction 10 1.1 Study Area 11 1.2 Scope of the Study 12 1.3 Acknowledgments 13 2 Available Data 14 2.1 General 15 2.2 Topography and Aerial Photography 15 2.3 Design Data and GIS Layers 15 2.4 Survey and Ground Data 17 2.5 Rainfall Data 18 2.5.1 Recorded Rainfall 18 2.5.2 Design Intensity Data 20 2.5.3 Probable Maximum Precipitation (PMP) 22 2.6 Surge and Tide Data 23 2.6.1 Static Surge Modelling 23 2.6.2 Simplified Surge Propagation Modelling 24 2.6.3 Tide Modelling 25 2.7 Historical Flood Records 25 2.7.1 General 25 2.7.2 Stream Gauging 25 2.7.3 Flood Questionnaire 27 2.8 Previous Studies 28 2.8.1 Townsville Port Access Hydraulic Assessment (2000) 28 2.8.2 Kirwan-Bohle Drainage Diversion, Louisa Creek Flood Study (1999) 28 2.8.3 Stuart Creek Flood Study (1997) 29 2.8.4 Bohle River Floodplain Management Study (2000) 29 2.8.5 Ross River Dam Design Hydrology (2003) 30 2.8.6 Ross River Dambreak Studies 31 3 Hydrology Modelling 32 3.1 Modelling Tools 33 3.2 Magnetic Island 34 3.2.1 Catchment Analysis 34 3.2.2 Adopted RAFTS Loss Models 35 3.2.3 RAFTS Model Verification 35 3.2.4 Design Modelling 36 3.3 Townsville Flood Plain 38 3.3.1 Catchment Analysis 38 3.3.2 RAFTS Model Calibration and Verification 41 3.3.3 Design Modelling 45 4 Hydraulic Modelling 48 4.1 Modelling Tools 49 4.2 MIKE11 Assessment – Magnetic Island 51 4.2.1 Model Development 51 4.2.2 Model Results 55 4.3 MIKE11 Assessment – Townsville Floodplain 56 4.3.1 Model Development 56 4.3.2 Model Calibration 57 4.3.3 Model Verification 60 Townsville Flood Hazard Assessment Study Revision A Phase 2 Report - Volume 1 - Flood Study December 2005 J:\MMPL\80377706\Administration\Flood Report\Phase 2\re-issue Nov 06\report.doc Page 3 of 84 Table of Contents - cont 4.3.4 Model Results 62 4.3.5 Sensitivity Assessment 63 4.4 MIKE21 Assessment – Townsville Floodplain 65 4.4.1 Model Development 65 4.4.2 Model Calibration 71 4.4.3 Model Results 73 4.5 Mitigation Option Assessment – Townsville Floodplain 74 5 Flood and Surge Inundation Maps 75 5.1 General 76 5.2 Flood Inundation 76 5.2.1 Magnetic Island 77 5.2.2 Townsville Floodplain 78 5.3 Storm Surge and Tidal Inundation 80 5.3.1 Townsville Floodplain 81 5.3.2 Pallarenda and Cungulla 82 6 References 83 Appendix A TCC Flood Map (March 1990) Appendix B Flood Questionnaire Appendix C Catchment Maps – Volume 2 Appendix D MIKE Modelling Results – Volume 1 / Volume 2 Appendix E Inundation Maps – Volume 2 Townsville Flood Hazard Assessment Study Revision A Phase 2 Report - Volume 1 - Flood Study December 2005 J:\MMPL\80377706\Administration\Flood Report\Phase 2\re-issue Nov 06\report.doc Page 4 of 84 Table of Contents - cont List of Tables Number Title Page 1 Summary of Available Rainfall Data 18 2 IFD Input Parameters for the Townsville Floodplain 21 3 Design Intensities for the Townsville Floodplain 21 4 IFD Input Parameters for Magnetic Island 21 5 Design Intensities for Magnetic Island 21 6 Short Duration PMP Rainfall Estimates for Magnetic Island 22 7 Short Duration PMP Rainfall Estimates for Townsville Floodplain 22 8 Summary of Storm Tide Statistics for Townsville Region 23 9 100 Year ARI Results – Townsville Port Access Study 28 10 Peak Discharge Results – Louisa Creek Flood Study 28 11 Peak Discharge Results – Stuart Creek Flood Study 29 12 Peak Discharge Results – Bohle River Overflows to Louisa Creek 29 13 Ranges for Catchment Parameters in RAFTS Models of Magnetic Island 34 14 Comparison of Peak Flows from RAFTS and Rational Method 36 15 Critical Duration Events for Magnetic Island 37 16 RAFTS Peak Discharge Results for Key Locations on Magnetic Island 37 17 Summary of Sub-Catchments for Townsville Floodplain 40 18 Ranges for Catchment Parameters in RAFTS Models of Townsville Floodplain 40 19 RAFTS Peak Discharge Comparison – Louisa Creek at Bayswater Road 45 20 RAFTS Peak Discharge Comparison – Stuart Creek 45 21 RAFTS Peak Discharge Comparison – Townsville Port Access Study 45 22 Model Grid Mesh Details 66 23 Adopted Roughness Values in MIKE21 Model 70 24 Summary of Maximum Discharges for Design Floods in MIKE21 73 25 Flood Inundation Mapping Characteristics – Magnetic Island 76 26 Flood Inundation Mapping Characteristics – Townsville Floodplain (MIKE11) 77 27 Flood Inundation Mapping Characteristics – Townsville Floodplain (MIKE21) 78 28 Surge/Tide Inundation Mapping Characteristics – Townsville Floodplain 81 29 Surge/Tide Inundation Mapping Characteristics – Pallarenda 82 30 Surge/Tide Inundation Mapping Characteristics – Cungulla 82 Townsville Flood Hazard Assessment Study Revision A Phase 2 Report - Volume 1 - Flood Study December 2005 J:\MMPL\80377706\Administration\Flood Report\Phase 2\re-issue Nov 06\report.doc Page 5 of 84 Table of Contents - cont List of Figures Figure Number Title Page 1 Study Area 11 2 Example of Rectified Photo Mosaic 16 3 Example of Stormwater Network GIS Layer 16 4 Example of Digital Contour Data 17 5 March 1990 Rainfall (1 Hour Intervals – Townsville AMO) 19 6 January 1998 Rainfall (1 Hour Intervals – Townsville AMO) 19 7 February 2002 Rainfall (1 Hour Intervals – Townsville Alert) 20 8 Storm Tide Statistics for Pallarenda (source: BPA, 1985) 23 9 Tidal Record at Townsville Harbour During Tropical Cyclone Althea 24 10 February 2002 Stream Gauge Record – Stuart Creek Alert 26 11 February 2002 Stream Gauge Record – Louisa Creek Alert 26 12 February 2002 Stream Gauge Record – Mysterton Alert 27 13 100 Year ARI Overflow Hydrograph from Bohle River 30 14 January 1998 Discharge Hydrograph at Gleesons Weir 31 15 February 2002 Gauge Locations and Spatial Distribution 42 16 January 1998 Gauge Locations and Spatial Distribution 43 17 March 1990 1998 Gauge Locations and Spatial Distribution 44 18 Comparison of 1998 Rainfall and 100 Year ARI Design Rainfall 46 19 Comparison of 1998 Intensities and 100 Year ARI Design Intensities 47 20 Picnic Bay MIKE11 Network 51 21 Nelly Bay MIKE11 Network 52 22 Arcadia (Geoffrey Bay and Alma Bay) MIKE11 Network 53 23 Horseshoe Bay MIKE11 Network 54 24 Townsville Floodplain MIKE11 Network 56 25 2002 MIKE11 Calibration – Comparison of Surveyed Levels 57 26 2002 MIKE11 Calibration – Mysterton Alert Gauge 58 27 2002 MIKE11 Calibration – Louisa Creek Alert Gauge 59 28 2002 MIKE11 Calibration – Stuart Creek Alert Gauge 59 29 1998 MIKE11 Verification – Comparison of Surveyed Levels 60 30 1990 MIKE11 Verification – Comparison of Inundation Patterns 61 31 Comparison of 2 Year ARI Inundation due to Increased Tide Level 64 32 Townsville MIKE21 Flood Model Extent 65 33 Townsville MIKE21 Model Topography (20m Grid) 66 34 Townsville MIKE21 Model Boundary Locations 67 35 Location of Source Point Inflow Locations 68 36 Location of Hydraulic Structures in the MIKE21 Model 69 37 MIKE21 Model Roughness Distribution Map 70 38 Thematic Map of Peak MIKE21 Level Comparison 72 39 1998 MIKE21 Calibration – Comparison of Surveyed Levels 72 Townsville Flood Hazard Assessment Study Revision A Phase 2 Report - Volume 1 - Flood Study December 2005 J:\MMPL\80377706\Administration\Flood Report\Phase 2\re-issue Nov 06\report.doc Page 6 of 84 Executive Summary Townsville Flood Hazard Assessment Study Revision A Phase 2 Report - Volume 1 - Flood Study December 2005 J:\MMPL\80377706\Administration\Flood Report\Phase 2\re-issue Nov 06\report.doc Page 7 of 84 Executive Summary Townsville City Council received funding under the Natural Disaster Risk Management Studies Program to undertake a Disaster Risk Management Study specific to flooding including a preliminary assessment of storm surge in coastal areas. Primary objectives of the Study included: quantifying flood inundation in Townsville and Magnetic Island a preliminary assessment of storm surge inundation in Pallarenda and Cungulla determining the flood hazards and the vulnerability of community and infrastructure, and identifying possible risk mitigation measures and strategies to allow proper and effective management of the identified risks. The Project Plan identified three distinct yet inter-related phases to the Study. This report addresses Phase 2, which require a comprehensive flood hazard assessment of Townsville and Magnetic Island, using both 1-D and 2-D hydraulic modelling techniques. The study has culminated in detailed inundation mapping of design flood events ranging from 2 Year ARI to Probable Maximum Flood (PMF), and a simplistic assessment of storm surge inundation of coastal areas.