THE UNIVERSITY OF QUEENSLAND SCHOOL OF CIVIL ENGINEERING TROPICAL CYCLONE ‘ROGER’ STORM SURGE ASSESSMENT J. STEWART, D. CALLAGHAN and P. NIELSEN RESEARCH REPORT CE162 CIVIL ENGINEERING RESEARCH REPORTS This report is one of a continuing series of Research Reports published by the School of Civil Engineering at the University of Queensland. Lists of recently-published titles of this series and of other publications are provided at the end of this report. Requests for copies of any of these documents should be addressed to the School Secretary. The interpretation and opinions expressed herein are solely those of the author(s). Considerable care has been taken to ensure accuracy of the material presented. Nevertheless, responsibility for the use of this material rests with the user. School of Civil Engineering The University of Queensland Brisbane QLD 4072 AUSTRALIA Telephone: (61 7) 3365 3619 Fax: (61 7) 3365 4599 URL: http://www.eng.uq.edu.au/civil/ First published in 2010 by Jared STEWART, David CALLAGHAN and Peter NIELSEN School of Civil Engineering The University of Queensland, Brisbane QLD 4072, Australia This book is copyright ISBN No. 978-1-74272-002-9 The University of Queensland, St Lucia QLD Tropical Cyclone ‘Roger’ Storm Surge Assessment by Jared STEWART Masters Student, School of Civil Engineering, The University of Queensland, Brisbane QLD 4072, Australia Mob.: (61 4) 0280 5321, Email: [email protected] David CALLAGHAN Lecturer, School of Civil Engineering, The University of Queensland, Brisbane QLD 4072, Australia Ph.: (61 7) 3365 3517, Fax: (61 7) 3365 4599, Email: [email protected] and Peter NIELSEN Associate Professor, School of Civil Engineering, The University of Queensland, Brisbane QLD 4072, Australia Ph.: (61 7) 3365 3510, Fax: (61 7) 3365 4599, Email: [email protected] RESEARCH REPORT No. CE162 ISBN 978-1-74272-002-9 School of Civil Engineering, The University of Queensland July 2010 ABSTRACT The consideration and accurate prediction of storm surge to ensure the protection of coastal communities and infrastructure is very important for coastal areas. While the basic processes which are responsible for storm surge are widely accepted and understood, there remain recorded storm surge events which have not been able to be fully explained using accepted methods and theories. A detailed investigation into one such storm surge event which resulted from Tropical Cyclone ‘Roger’ in 1993 has been completed with the use of a hydrodynamic model and hindcast meteorological data. A MIKE 21 FM model was developed and simulated using hindcast wind and pressure data. The effect of wave radiation stresses and tides on the modelled surge was also investigated. The modelled storm surge was generally found to under-predict the tidal anomalies recorded during the event. The inclusion of tides in the model was not found to affect the modelled surge, while the inclusion of wave radiation stresses was found to improve the fit between the modelled and recorded surge. However, there remained areas of the recorded tidal anomalies which were not well replicated by the model or easily rationalised. The two key recommendations of the study are for the simulation of additional historical storm surge events and the permanent installation of current recording instrumentation (i.e. bottom mounted ADCP) on offshore tide stations. Keywords: Storm Surge Modelling, Tropical Cyclone Roger, Storm Surge, Wave Setup, Gold Coast Seaway. ii TABLE OF CONTENTS Page Abstract ii Keywords ii Table of contents iii List of symbols v 1. Introduction 1 2. Background 3 2.1. Tropical Cyclones 2.2. Storm Surge 2.3. Storm surge prediction in south east Queensland 2.4. Tropical Cyclone ‘Roger’ – March 1993 3. Storm surge modelling 33 3.1. Models 3.2. Model forcings 3.3. Bathymetry 3.4. Grid/mesh size 3.5. Parameters 4. Model Setup 42 4.1. Model code 4.2. Domain 4.3. Bathymetry 4.4. Meteorological input 4.5. Parameters 4.6. Tidal constituents 4.7. Wave simulation 4.8. Additional notes 5. Results 63 5.1. Initial simulation results 5.2. Sensitivity analysis results 6. Discussion 81 6.1. Pumicestone Passage to Mooloolaba surge iii 6.2. Wind stress and wave radiation simulation results 6.3. Wave setup vs. wave radiation stresses 6.4. Other processes not considered 6.5. Coastline representation 6.6. Comparison with 1d analytical solution 6.7. Anomalies in anomalies 6.8. Summary of results 7. Conclusions 94 8. Acknowledgements 96 8.1. Assistance 8.2. Data APPENDICES Appendix A - Tidal Anomaly Plots 97 Appendix B - NCEP DOE comparison with observed parameters 109 Appendix C - Rainfall data for March 1993 156 REFERENCES 164 Internet references 167 Open Access Repositories 168 Bibliographic reference of the Report CH77/10 169 iv LIST OF SYMBOLS The following symbols are used in this report: CD free surface drag coefficient; CB bottom drag coefficient; F force (N); f Coriolis parameter; g gravity constant (m/s2); h water depth (m); h0 water depth at the coastline (m); Horms deepwater RMS wave height (m); Hsig significant wave height (m); L continental shelf width (m); s numerical model grid spacing; Sxx wave radiation stress in the shore normal direction (Pa); t time (s); U absolute wind velocity (m/s); U10 absolute 10m wind velocity (m/s); Ux x component of wind velocity (m/s); Uy y component of wind velocity (m/s); u current velocity (m/s); x distance normal to the shoreline (m); z vertical distance (m) positive upwards, with z = 0 at the bed; α continental shelf slope (radians); η water elevation (m); ηc water elevation at the SWL shoreline (m); ηs water elevation at the MWL shoreline (m); Ω angular velocity of the earth (7.29 x 10-5 radians/second); φ latitude (degrees); 3 ρa air density (kg/m ); ρ water density (kg/m3); τb bed shear stress (Pa); τw wind shear stress (Pa); Abbreviations 2D two-dimensional 3D three-dimensional ADCP Acoustic Doppler Current Profiler AEST Australian Eastern Standard Time v AHD Australian Height Datum AWN Australian Weather News BOM Bureau of Meteorology BPA Beach Protection Authority DERM Department of Environment and Resource Management (previously EPA) ECL East Coast Low (low pressure weather system) GPS Global Positioning System HAT Highest Astronomical Tide LAT Lowest Astronomical Tide MHL Manly Hydraulics Laboratory MSL Mean Sea Level MSLP Mean Sea Level Pressure MSQ Maritime Safety Queensland MWL Mean Water Level NSW New South Wales QLD Queensland RMS Root Mean Square RMSE Root Mean Square Error SEQ South East Queensland SWL Still Water Level TC Tropical Cyclone UTC Universal Time Convention vi 1. INTRODUCTION In today’s world there are numerous natural hazards which have the potential to cause large scale destruction, loss of lives and interruption to vital services and trade. These include floods, bushfires, earthquakes, tropical cyclones, tsunamis and landslides. Of these natural disasters tropical cyclones represent a significant hazard to coastal communities potentially affected by tropical cyclones. In Australia between the period of 1967 to 1999, approximately 154 deaths and 8.5 billion dollars in damages were attributable to tropical cyclones, accounting for approximately 24% of the estimated costs caused by natural disasters in Australia (BTE 2001). Globally, there have also been numerous natural disasters attributable to tropical cyclones, notably the devastation caused by a cyclone in the Bay of Bengal in November 1970 which resulted in approximately 300,000 deaths (Frank & Husain 1971) and Hurricane Katrina in 2005 which resulted in approximately 2000 deaths and estimated total damages of US 250billion (Glantz 2008). The elevation of the mean sea level during tropical cyclones is perhaps the most dangerous hazard associated with tropical cyclones (BOM 2009a, GA 2009). Referred to as storm surge, this process is caused by strong onshore winds and low atmospheric pressure which combine to elevate the sea level along coastlines, for periods of hours to days (Simpson & Riehl 1981). The consideration and accurate prediction of storm surge to ensure the protection of coastal communities and infrastructure is therefore very important for coastal areas (U.S. ACERC 1977). While the basic processes which are responsible for storm surge are widely accepted and understood, there remain recorded storm surge events which have not been able to be fully explained using accepted methods and theories. This report describes a project undertaken to assess such a storm surge which resulted from Tropical Cyclone ‘Roger’ in 1993. The aim of the project was to better understand storm surge components and their relative magnitude during Tropical Cyclone ‘Roger’. This event was selected for this project as it generated a notable storm surge in areas of south east Queensland despite being a relatively weak cyclone which did not cross the coastline. In order to assess the storm surge resulting from Tropical Cyclone ‘Roger’, a hydrodynamic model has been established to model the event and the resulting storm surge. The development of the model, including the data used in the model, adopted parameters, model sensitivity analysis, and the model results are discussed. The results from the model have also been compared with a simplified 1-d analytical solution. A review of storm surge assessments for SEQ, including a review of studies which have determined appropriate guidelines for storm surge levels, has also been undertaken to compare the storm surge recorded during Tropical Cyclone ‘Roger’ with such guidelines. Additionally, a review of previous 1 modelling of storm surges has been undertaken to assess the methods and values of key parameters adopted in previous studies. This report is structured as follows: Section 2 covers the background of the project including definition of the terminology used throughout the report, theory behind the basic processes of storm surge generation, a summary of the history of storm surge prediction in south-east Queensland, and a discussion of Tropical Cyclone ‘Roger’ including presentation of data recorded during the event.