City Wide Flood Constraints Project Townsville City Council 24-Jun-2014 Black River Flood Study Base-line Flooding Assessment J:\MMPL\60285746\8. Issued Docs\8.6 Clerical\flooding assessment\final copy\report.docx Revision A – 24-Jun-2014 Prepared for – Townsville City Council – ABN: 44 741 992 072 AECOM City Wide Flood Constraints Project Black River Flood Study Black River Flood Study Base-line Flooding Assessment Client: Townsville City Council ABN: 44 741 992 072 Prepared by AECOM Australia Pty Ltd 21 Stokes Street, PO Box 5423, Townsville QLD 4810, Australia T +61 7 4729 5500 F +61 7 4729 5599 www.aecom.com ABN 20 093 846 925 24-Jun-2014 Job No.: 60285746 AECOM in Australia and New Zealand is certified to the latest version of ISO9001, ISO14001, AS/NZS4801 and OHSAS18001. © AECOM Australia Pty Ltd (AECOM). All rights reserved. AECOM has prepared this document for the sole use of the Client and for a specific purpose, each as expressly stated in the document. 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Issued Docs\8.6 Clerical\flooding assessment\final copy\report.docx Revision A – 24-Jun-2014 Prepared for – Townsville City Council – ABN: 44 741 992 072 AECOM City Wide Flood Constraints Project Black River Flood Study Quality Information Document Black River Flood Study Ref 60285746 Date 24-Jun-2014 Prepared by Wen Han Ooi Reviewed by Sally Williams Revision History Authorised Revision Revision Date Details Name/Position Signature 0 4-Jun-2014 Draft Issue Anton Appelcryn Principal Civil Engineer A 24-Jun-2014 Final for Issue Anton Appelcryn Principal Civil Engineer J:\MMPL\60285746\8. Issued Docs\8.6 Clerical\flooding assessment\final copy\report.docx Revision A – 24-Jun-2014 Prepared for – Townsville City Council – ABN: 44 741 992 072 AECOM City Wide Flood Constraints Project Black River Flood Study Table of Contents Executive Summary i 1.0 Introduction 1 1.1 Overview 1 1.2 Study Area 1 1.3 Scope of Works 1 1.4 Study Approach 3 1.5 Spatial Data 3 1.6 Previous Reports 3 2.0 Hydrology Assessment 5 2.1 Overview 5 2.1.1 Catchment Description 5 2.1.2 Assessment Approach 5 2.2 Design Rainfall 7 2.2.1 Up to 100-year ARI 7 2.2.2 Extreme Events (500-year ARI and Probable Maximum Precipitation) 8 2.3 Runoff Routing Method 9 2.3.1 Sub-Catchment Delineation 9 2.3.2 Sub-Catchment Parameters 9 2.4 Hydrologic Model Calibration 11 2.4.1 Flood Frequency Analysis 11 2.4.2 Comparison between Design Storms and FFA 14 2.5 Rain-on-Grid Method – Local Runoff 15 3.0 Hydraulic Modelling 17 3.1 Overview 17 3.2 MIKE FLOOD Hydraulic Model 17 3.2.1 MIKE 11 17 3.2.2 MIKE 21 17 3.3 Model Development 17 3.3.1 Model Grid 17 3.3.2 Hydraulic Structures 20 3.3.3 Boundary Conditions and local source points 25 3.3.4 Roughness 25 3.4 Model Calibration 28 3.4.1 Model Calibration against the January 1998 Event 28 3.5 Design Flood Critical Duration Assessment 29 4.0 Design Flood Assessment 31 4.1 Flooding across the Study Area 31 4.2 Major Arterial Roads 33 4.3 Hydraulic Grade Line 35 5.0 Conclusions and Recommendations 37 5.1 Conclusions 37 5.2 Recommendations 38 6.0 References 39 Appendix A Flood Maps A Appendix B XP RAFTS Model Parameters B Appendix C Black River Long Section Profile C J:\MMPL\60285746\8. Issued Docs\8.6 Clerical\flooding assessment\final copy\report.docx Revision A – 24-Jun-2014 Prepared for – Townsville City Council – ABN: 44 741 992 072 AECOM City Wide Flood Constraints Project Black River Flood Study List of Tables Table EX-1 - Flooding Assessment Summary for Black River Flood Study................................... ii Table 2-1 IFD Input Parameters .............................................................................................. 7 Table 2-2 Extreme Rainfall Events Intensity (mm/h) ............................................................ 8 Table 3-1 Details of culverts modelled using MIKE11 ....................................................... 20 Table 3-2 Details of bridges modelled using MIKE11 in the Middle Bohle Model .......... 23 Table 3-3 Hydraulic Roughness Values .............................................................................. 25 Table 4-1 Flooding Assessment Summary for the Black River Main Channel ............... 31 Table 4-2 Water Depth over main roads at selected waterway crossings (m) ................ 33 Table B1 XP-RAFTS Model Parameters ............................................................................. B-1 List of Figures Figure 1-1 Locality Plan ............................................................................................................ 2 Figure 2-1 Location and Extents of Model Catchments ........................................................ 6 Figure 2-2 Black River Catchment ......................................................................................... 10 Figure 2-3 Black River FFA using Log-Pearson III .............................................................. 11 Figure 2-4 January 1998 Rainfall and Black River IFD comparison .................................. 12 Figure 2-5 January 1998 XP-RAFTS results ......................................................................... 13 Figure 2-6 Comparison between Design Storms and FFA ................................................. 14 Figure 2-7 Imperviousness Map ............................................................................................ 16 Figure 3-1 Model Extents in relation to previous studies ................................................... 18 Figure 3-2 Black River Model Grid ........................................................................................ 19 Figure 3-3 Hydraulic Structures ............................................................................................ 24 Figure 3-4 Model Boundary Conditions ................................................................................ 26 Figure 3-5 Roughness Map .................................................................................................... 27 Figure 3-6 MIKE FLOOD Model Calibration – January 1998 Flood Event ......................... 28 Figure 3-7 100-year ARI Critical Duration Assessment ....................................................... 30 Figure 4-1 Location of flooding affecting major arterial roads .......................................... 34 Figure 4-2 Longitudinal Profile Plan View ............................................................................ 36 Figure C-1 Black River Long Section Profile .......................................................................... 1 J:\MMPL\60285746\8. Issued Docs\8.6 Clerical\flooding assessment\final copy\report.docx Revision A – 24-Jun-2014 Prepared for – Townsville City Council – ABN: 44 741 992 072 AECOM City Wide Flood Constraints Project i Black River Flood Study Executive Summary AECOM Australia Pty Ltd (AECOM) was engaged by Townsville City Council (TCC) to carry out the Black River Flood Study to determine the existing flood characteristics of the Black River catchment as part of the TCC City Wide Flood Constraints Project. The focus area for this study is the Black River catchment, approximately 20 km west of Townsville City. The Saunders Creek and Stony Creek catchments were also included to facilitate the representation of flows between catchments during extreme flood events. The Black River Flood Study builds on a number of previous flood assessments carried out in the area of interest. Coarse scale hydrologic and hydraulic models developed by AECOM have been updated to reflect recent changes within the floodplain and refined to enable the assessment of a wider range of flood events. The models were also re-calibrated to match measured data from historical flood events. XP-RAFTS hydrological models of the Black River, Saunders Creek and Stony Creek catchments previously developed by AECOM as part of the Deeragun Flood Study formed a basis for this study. The Black River hydrologic model was updated and refined to take into account changes in the land use, river conditions and development of land within the catchment. This model was then calibrated to the January 1998 and February 2008 Black River flood events. A MIKE FLOOD hydraulic model was developed to represent the existing Black River catchment conditions. The model consisted of a 10 m grid MIKE 21 overland flow model dynamically linked to several one-dimensional (MIKE 11) branches representing the major structures throughout the floodplain. The model topography was developed from a range of datasets for the study area, which included hydrographic survey of the lower reaches of the Black River, as well as the latest available LiDAR topographic survey data (2012). The Rain-on-Grid method was applied across the majority of the sub-catchments within the hydraulic model extent to represent local runoff at a 10 m grid scale. Upstream river inflows to the hydraulic model