KINGSTON BEACH FLOOD STUDY KINGBOROUGH COUNCIL TABLE OF CONTENTS Executive Summary ................................................................................................................................................ 1 1 Introduction .................................................................................................................................................... 3 1.1 Study Location ....................................................................................................................................... 3 1.2 Context and Scope ................................................................................................................................ 4 1.3 Study Objectives .................................................................................................................................... 4 1.4 Kingston Beach Flood History ............................................................................................................... 4 2 Study Approach .............................................................................................................................................. 6 2.1 Catchment Description ......................................................................................................................... 6 2.2 Review of Available Data ....................................................................................................................... 8 2.2.1 Previous Flood Studies ...................................................................................................................... 8 2.2.2 Site Inspection ................................................................................................................................ 10 2.2.3 GIS Information ............................................................................................................................... 10 2.2.4 Topographic Data ............................................................................................................................ 10 2.2.5 Survey & Bathymetric Data ............................................................................................................. 10 2.2.6 Aerial Photography ......................................................................................................................... 10 2.2.7 Land Use Data ................................................................................................................................. 11 2.2.8 Design Rainfall ................................................................................................................................ 12 2.2.9 Climate Change ............................................................................................................................... 14 2.2.10 Entrance Boundary Condition .................................................................................................... 14 2.2.11 Sea Level Rise ............................................................................................................................. 15 2.2.12 Ocean Tide Data ......................................................................................................................... 15 3 Community Engagement .............................................................................................................................. 17 4 Model Development ..................................................................................................................................... 18 4.1 Modelling Approach ............................................................................................................................ 18 4.2 Software Overview .............................................................................................................................. 19 4.3 Hydrological Model ............................................................................................................................. 19 4.3.1 Catchment Delineation ................................................................................................................... 19 4.3.2 Design Rainfall ................................................................................................................................ 22 i 4.3.3 Rainfall Losses ................................................................................................................................. 23 4.3.4 Fraction Impervious ........................................................................................................................ 24 4.4 Hydraulic Model .................................................................................................................................. 25 4.4.1 Extents and layout .......................................................................................................................... 25 4.4.2 Computational Grid ........................................................................................................................ 26 4.4.3 Hydraulic Roughness ....................................................................................................................... 26 4.4.4 Structures........................................................................................................................................ 27 4.4.5 Ocean Boundary Data ..................................................................................................................... 29 4.5 Model Calibration ............................................................................................................................... 31 4.5.1 Selection of Calibration Events ....................................................................................................... 31 4.5.2 Calibration Data .............................................................................................................................. 31 4.5.3 Streamflow Data ............................................................................................................................. 34 4.5.4 Adopted Model Parameters ........................................................................................................... 34 4.6 Observed and Simulated Flood Conditions ......................................................................................... 34 4.7 Flood Frequency Analysis AND Design Flood Estimates ..................................................................... 38 4.8 Sensitivity Analysis .............................................................................................................................. 40 4.8.1 Climate Change Impact on Rainfall Intensity .................................................................................. 40 4.8.2 Hydrologic Roughness..................................................................................................................... 40 4.8.3 Rainfall Losses ................................................................................................................................. 42 4.8.4 Sea Level Boundary (Phasing) ......................................................................................................... 43 4.8.5 Coastal Berm Conditions ................................................................................................................. 44 5 Design Flood Conditions ............................................................................................................................... 46 5.1 Coincident Flooding ............................................................................................................................ 46 5.1.1 Ocean Derived Flood Events ........................................................................................................... 47 5.2 Design Flood Hydrographs .................................................................................................................. 48 6 Design Flood Results ..................................................................................................................................... 50 6.1 Catchment Derived Flood Events ........................................................................................................ 50 6.2 Joint Catchment and Ocean Derived Flood Events ............................................................................. 50 6.3 Flood Hazard ....................................................................................................................................... 51 ii 6.4 Discussion ............................................................................................................................................ 52 7 Emergency management .............................................................................................................................. 53 7.1 Flood Emergency Plan ......................................................................................................................... 53 7.2 Assessment of Critical Infrastructure .................................................................................................. 53 7.3 Flood Warnings ................................................................................................................................... 54 7.4 Evacuation Route Assessment ............................................................................................................ 54 8 Potential Mitigation Measures ....................................................................................................................