Department of Natural Resources and Mines Department of Emergency Services Environmental Protection Agency OCEANOCEAN HAZARDSHAZARDS ASSESSMENTASSESSMENT -- StageStage 11 Report March 2001 Review of Technical Requirements In association with: Numerical Modelling Marine and Risk Modelling Assessment Unit QQuueeeennssllaanndd CClliimmaattee CChhaannggee aanndd CCoommmmuunniittyy VVuullnneerraabbiilliittyy ttoo TTrrooppiiccaall CCyycclloonneess OCEAN HAZARDS ASSESSMENT - Stage 1 March 2001 SEA Doc. No. J0004-PR001C Department of Natural Resources and Mines, Queensland Department of Emergency Services, Queensland Environmental Protection Agency, Queensland Bureau of Meteorology, Queensland Systems Engineering Australia Pty Ltd, Queensland QNRM01056 ISBN: 0 7345 1788 2 General Disclaimer Information contained in this publication is provided as general advice only. For application to specific circumstances, advice from qualified sources should be sought. 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Front cover images have been provided courtesy of the Department of Emergency Services, from the Brisbane Storm Chasers Homepage and the Queensland State Library Enquiries should be addressed to: Steven Crimp Department of Natural Resources and Mines 80 Meiers Road, Indooroopilly Brisbane, QLD 4068 Queensland Government Queensland Climate Change and Community Vulnerability to Tropical Cyclones Ocean Hazards Assessment - Stage 1 Contents List of Tables vii List of Figures viii List of Contributors xi Acknowledgements xii 1. EXECUTIVE SUMMARY 1 2. TROPICAL CYCLONE INDUCED OCEAN HAZARDS IN QUEENSLAND 2 2.1 Overview 2 2.2 Tropical Cyclones 4 2.3 Extreme Waves 6 2.4 Storm Surge 8 2.5 Storm Tide 10 2.6 References 13 3. TROPICAL CYCLONE CLIMATOLOGY OF QUEENSLAND 14 3.1 Historical Summary of Incidence and Intensity 14 3.2 Statistical Analysis of Post 1959/60 Data 16 3.3 Climatic Variability 23 3.4 Conclusions and Recommendations 27 3.5 References 27 4. GREENHOUSE CLIMATE CHANGE AND SEA LEVEL RISE 29 4.1 The Global Warming Process 29 4.2 Evidence of Climate Change 30 4.3 Latest Global Projections 32 4.4 Major Weather Systems and Global Climate Change 33 4.5 Impact on the Oceans 34 4.6 Impact on Coastal Zones and Small Islands 35 4.7 Australian Regional Predictions and Impacts 37 J0004-PR0001C i March 2001 Queensland Government Queensland Climate Change and Community Vulnerability to Tropical Cyclones Ocean Hazards Assessment - Stage 1 4.8 Conclusions and Recommendations 37 4.9 References 38 5. TROPICAL CYCLONE WIND AND PRESSURE MODELLING 41 5.1 The Need for Simplified Models 41 5.2 Basic Model Characteristics 42 5.3 Boundary Layer Representation 44 5.4 Forward Motion Asymmetry 45 5.5 A Typical Parametric Wind Field Representation 46 5.6 Historical Development of Windfield Models 48 5.6.1 Earliest Studies 48 5.6.2 US Army Corps of Engineers Impetus 48 5.6.3 Growth of Applications 49 5.6.4 Improving Theory and Observations 51 5.6.5 More Contemporary Developments 52 5.6.6 Transient Wind Features 55 5.6.7 Summary of Model Developments 56 5.7 Conclusions and Recommendations 57 5.8 References 58 6. NUMERICAL MODELLING OF TROPICAL CYCLONE STORM SURGE 67 6.1 Background and Introduction 67 6.2 Essential Physics – The Long Wave Equations 68 6.2.1 Equations of Motion 68 6.2.2 Boundary Conditions 70 6.2.3 Surge-tide Interactions 72 6.3 External Forcing 72 6.3.1 Wind field modelling 72 6.3.2 Parameterisation of surface stress 73 6.4 Solution Procedures 76 6.4.1 Finite Difference versus Finite Element 76 6.4.2 Explicit vs Implicit 77 6.4.3 Sizes for spatial step and time step 78 6.4.4 Open Boundary Conditions 79 6.4.5 Overland Flooding and Drying 82 6.5 Recent Developments 85 6.5.1 Surge-Wave Interactions 85 6.6 Conclusions and Recommendations 88 6.7 References 91 J0004-PR0001C ii March 2001 Queensland Government Queensland Climate Change and Community Vulnerability to Tropical Cyclones Ocean Hazards Assessment - Stage 1 7. NUMERICAL MODELLING OF TROPICAL CYCLONE WIND WAVES 99 7.1 Introduction 99 7.2 The Physics of Wind-Wave Evolution 99 7.2.1 Governing Equations 99 7.2.2 Source Terms 100 7.3 Numerical Modelling of Waves 101 7.3.1 Introduction 101 7.3.2 Source Term Representation 102 7.3.3 First Generation Models 102 7.3.4 Second Generation Models 104 7.3.5 Third Generation Models 105 7.4 Computational Aspects 106 7.4.1 Advection of Energy 107 7.4.2 Computational Grids 110 7.4.3 Initial and Boundary Conditions 111 7.5 The Tropical Cyclone Wave Field 111 7.6 Tropical Cyclone Wave Spectra 116 7.6.1 JONSWAP Representation of Tropical Cyclone Spectra 118 7.6.2 Donelan et al. (1985) representation of Tropical Cyclone Spectra 121 7.7 Conclusions and Recommendations 123 7.7.1 Choice of Model Physics 123 7.7.2 Grid Considerations 124 7.7.3 Dissipation on Reefs 125 7.8 References 125 8. ESTIMATION OF WAVE SETUP AND RUNUP 131 8.1 Introduction 131 8.2 Waves in the Surf Zone 131 8.2.1 The Surf Similarity Parameter 132 8.2.2 Breaker Types 132 8.2.3 Breaker Heights 133 8.2.4 Wave Height to Water Depth Ratio after Breaking 133 8.2.5 Surf Beat 134 8.3 The Shape of the Surf Zone Mean Water Surface 134 8.3.1 Terminology and Definitions 134 8.3.2 Wave Setdown 136 8.3.3 Wave Setup 136 8.3.4 Shoreline Setup 138 8.3.5 Wave Effects on River Tail-water Levels 139 8.4 Swash and Runup Heights 141 8.4.1 Introduction 141 8.4.2 Runup heights for Regular Waves 141 8.4.3 Runup Heights for Irregular Waves 142 8.4.4 Extreme Runup Levels 143 8.5 Wave Setup on Coral Reefs 144 J0004-PR0001C iii March 2001 Queensland Government Queensland Climate Change and Community Vulnerability to Tropical Cyclones Ocean Hazards Assessment - Stage 1 8.6 Conclusions and Recommendations 148 8.7 References 149 9. STORM TIDE STATISTICS 150 9.1 Introduction 150 9.2 The Historical Context 150 9.3 The Need for Revision and Update 153 9.4 The Prediction Problem 155 9.5 Estimation of Risks Without Long-Term Measured Data 156 9.5.1 The "Design Storm" Approach 156 9.5.2 The "Hindcast" Approach 156 9.5.3 Simulation Techniques 157 9.6 Essential Elements for Statistical Storm Tide Prediction 160 9.6.1 Representation of the Storm Climatology 160 9.6.2 Representation of the Deterministic Forcing and Ocean Response 161 9.6.3 Representation of the Combined Storm Tide Event 162 9.7 Conclusions and Recommendations 163 9.8 References 164 10. STORM SURGE MODEL VALIDATION AND SENSITIVITY TESTING 169 10.1 Selection of Hindcast Storms 169 10.2 Details of the Numerical Storm Surge Modelling 169 10.3 The January 1918 Cyclone at Mackay 177 10.3.1 Available Tropical Cyclone Data 177 10.3.2 Available Storm Tide Data 178 10.3.3 Reconstruction of the Event 182 10.3.4 Model and Data Comparisons 188 10.3.5 Implications for Storm Surge Modelling 191 10.3.6 Tidal Modelling 192 10.3.7 Storm Surge Modelling 193 10.3.8 References 197 10.4 Tropical Cyclone Althea December 1971 at Townsville 198 10.4.1 Available Data 198 10.4.2 Reconstruction of the Event 203 10.4.3 Implications for Storm Surge Modelling 214 10.4.4 Tidal Modelling 215 10.4.5 Storm Surge Modelling 215 10.4.6 References 224 10.5 Tropical Cyclone Ted December 1976 at Burketown 225 10.5.1 Available Data 225 10.5.2 Reconstruction of the Event 228 10.5.3 Implications for Storm Surge Modelling 235 10.5.4 Tidal Modelling 236 10.5.5 Storm Surge Modelling 236 J0004-PR0001C iv March 2001 Queensland Government Queensland Climate Change and Community Vulnerability to Tropical Cyclones Ocean Hazards Assessment - Stage 1 10.5.6 References 243 10.6 Tropical Cyclone Steve February 2000 at Cairns 244 10.6.1 Available Data 244 10.6.2 Reconstruction of the Event 248 10.6.3 Implications for Storm Surge Modelling 257 10.6.4 Tidal Modelling 258 10.6.5 Storm Surge Modelling 258 10.6.6 References 264 10.7 Summary and Conclusions 265 11. SYSTEM DESIGN CONSIDERATIONS FOR STORM TIDE PREDICTION 268 11.1 Storm Tide Warning - the MEOW Approach 269 11.1.1 The Envisaged BMRC Procedure 269 11.1.2 Conclusions 271 11.2 Storm Tide Planning - Statistical Approaches 271 11.3 A Suggested Hybrid Approach 273 11.4 Storm Surge Model Domains for the Queensland Coast 276 11.4.1 Selection Rationale 277 11.4.2 Model Domain Specification 277 11.5 Estimating Model Simulation Times and Storage Requirements 279 11.5.1 Model Requirements 280 11.5.2 MEOW Parameter Selection 282 11.6 Conclusions and Recommendations 286 11.7 References 287 12.