Physical Processes of a Shallow Subtropical Estuarine System: Coombabah Lake, Gold Coast, Australia
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Physical Processes of a Shallow Subtropical Estuarine System : Coombabah Lake, Gold Coast, Australia Author Ali, Ayub Published 2010 Thesis Type Thesis (PhD Doctorate) School School of Engineering DOI https://doi.org/10.25904/1912/1067 Copyright Statement The author owns the copyright in this thesis, unless stated otherwise. Downloaded from http://hdl.handle.net/10072/366810 Griffith Research Online https://research-repository.griffith.edu.au Physical Processes of a Shallow Subtropical Estuarine System: Coombabah Lake, Gold Coast, Australia Ayub Ali BSc in Civil Engineering, MSc in Hydroinformatics (Netherlands) Griffith School of Engineering Science, Environment, Engineering and Technology Griffith University Submitted in fulfilment of the requirements of the degree of Doctor of Philosophy February 2010 Declaration This work has not previously been submitted for a degree or diploma in any university. To the best of my knowledge and belief, the thesis contains no material previously published or written by another person except where due reference is made in the thesis itself. ______________ Ayub Ali February 2010 i ii Acknowledgements After four years of study, which was full of exciting new learning experiences, albeit far away from my beloved Country, Bangladesh, I have succeeded to complete my PhD study in Griffith University, Gold Coast, Queensland, Australia. Here, I would like to take the opportunity to express my sincere appreciation and deep gratitude to those who assisted me in my work and supported me in one way or another during this particular period. I like to express my great respect and gratitude to my principal supervisor Charles Lemckert for his kind supervision, excellent guidance, continuous encouragement and valuable advice and suggestions during all stages of my study. He was always very helpful for discussion about research and career development. I was constantly inspired by your ability to manage your amazing academic career, adoring wife and five children – thank you so much for all of my PhD experiences. I like to express my sincere thanks and appreciation to my associate supervisor Dr Hong Zhang for her guidance and cooperation during this study especially with numerical modelling. I like to thank all the research students and my friends forever, at Griffith University, who helped me during my Candidature: Ryan J K Dunn, Nathan Benfer, Peta Williams and Johann Gustafson for helping me in data collection. Thanks to the lab technicians who helped me in preparation and installation of the data collection devices. Thanks to other PhD students whom I shared my office with especially Hassan Jabur and Mainul Islam for their daily accompany. The author is grateful to DHI Water and Environment for making the MIKE modelling software available for this study. Thanks to the Centre for Infrastructure and Environmental Management (CIEM), Griffith School of Engineering and Griffith University for providing financial support and necessary facilities to make this research possible. And most importantly, I wish to extend my profound gratitude to my beloved wife and kids for their continuous sacrifice and inspiration to make this study successful. I would iii like to extend my sincere thanks to my brothers, sisters and relatives who all supported me whole-heartedly for their moral support during my long stay away from them. Ayub Ali Gold Coast QLD, Australia iv Dedicated to my deceased parents Who could be extremely happy with this achievement If they were alive today. v vi List of Publications Below is a list of articles that were written and, either published or submitted for publication during the thesis candidature: Publications directly related to this thesis: Ali, A. and Lemckert, C.J., 2009. A traversing system to measure bottom boundary layer hydraulic properties, Estuarine Coastal and Shelf Science. doi:10.1016/j.ecss.2009.04.017 Ali, A., Lemckert, C.J. and Dunn, R.J.K., 2010. Salt fluxes in a very shallow sub- tropical estuary. Journal of Coastal Research., 26(3), 436-443. Ali, A., Lemckert, C.J., Zhang, H. and Dunn, R.J.K., 2009b. Sediment dynamics of a very shallow sub-tropical estuarine system – Coombabah Lake, Gold Coast, Australia. Estuarine, Coastal and Shelf Science (under revision). Ali, A., Zhang, H. and Lemckert, C.J., 2009c. Numerical study of the hydrodynamics of a very shallow estuarine system - Coombabah Lake, Gold Coast, Australia. Journal of Coastal Research, SI 56, 922-926. Dunn, R.J.K., Ali, A., Lemckert, C.J., Teasdale, P.R., and Welsh, D.T., 2007. Short- term variability of physio-chemical parameters and the estimated transport of filterable nutrients and chlorophyll-a in the urbanised Coombabah Lake and Coombabah Creek system, southern Moreton Bay, Australia. Journal of Coastal Research, SI 50, 1099-1105. Additional publications to that which makes up this thesis: Ali, A., Mynett, A.E. and Azam, M.H., 2007. Sediment Dynamics in the Meghna Estuary, Bangladesh: A Model Study. Journal of Waterway, Port, Coastal and Ocean Engineering, 133 (4), 255-263. Ali, A., Maraqa, M.A., Imran, H.D., Hamza, W. and Al Awadi, S. (2009). Effects of discharge characteristics on pollutant concentration at Jebel Ali Harbor, Dubai- UAE: A case study. Journal of Aquatic Ecosystems Health & Management (submitted). vii Maraqa, M.A., Ali, A., Imran, H.D., Hamza, W., and Al Awadi, S., 2008. Simulation of the hydrodynamic regime of Jebel Ali Harbor, Dubai-UAE. Journal of Aquatic Ecosystems Health & Management, 11 (1), 105-115. Maraqa, M.A., Ali, A. and Khan, N., 2007. Modelling Selected Water Quality Parameters at Jebel Ali Harbour, Dubai-UAE. Journal of Coastal Research, SI 50, 819-824. viii Abstract Estuaries are of immense importance to many communities. It has been estimated that 60 to 80 % of commercial marine fishery resources depend on estuaries for part, or all of, their life cycle. The characteristics of estuarine flow, water quality and sediment conditions are important as they play a critical role in the functionality and health of these systems. This study utilised both field data and numerical modelling technique to help enhance our understanding of the physical processes of a very shallow subtropical estuarine system. This study first quantified various salt flux components within the shallow subtropical estuarine system Coombabah Lake in Gold Coast, Queensland, Australia to better understand the system’s physical processes for assisting future management decisions in this ecologically and economically significant region. Residual water transport was identified as the dominant factor influencing residual salt transport, which alternates direction frequently. This study then developed a new simple and robust traversing system to measure flow properties within estuarine bottom boundary layers to estimate two important parameters used in numerical modelling of aquatic systems: bed shear stress and bed roughness height. Four commonly-employed techniques: (1) Log-Profile; (2) Reynolds stress; (3) Turbulent Kinetic Energy; and (4) Inertial Dissipation used to estimate bed shear stresses from velocity measurements were also compared. Bed shear stresses estimated with these four methods agreed reasonably well; of these, the Log Profile method was found to be most useful and reliable for the unstratified conditions studied. A three-dimensional hydrodynamic model with unstructured meshes utilising the MIKE3 FM modelling system and simulated the hydrodynamic regime was set up for Coombabah Lake to assist with enhancing our understanding of the hydraulic properties within this shallow sub-tropical estuarine system. The sensitivity of calibration parameters of a very shallow estuarine model was also investigated. The model utilised the hydraulic data collected by the newly developed traversing system and that collected ix during the first part of the study used to examine salt flux dynamics. The hydrodynamic regime of the lake was found to be favourable for settlement of suspended sediments. The results also revealed that the correct bathymetry is the most important parameter for accurate modelling, followed by appropriate bed roughness in the numerical scheme for very shallow environments. This study finally provided an understanding of the sediment dynamics within Coombabah Lake and the surrounding waters. It utilised ten days of observed hydrodynamic and sediment data and employed the three-dimensional model with unstructured meshes utilising the MIKE3 FM modelling system. Sediment dynamics of the lake were found to be dominated by advection process driven by tides with wave and wind playing minor roles – even though the system was shallow. Simulation results agreed well with field data and supported the aforementioned findings. Correlation between TSS and turbidity was very poor; therefore, the employed automatic data logging system (turbidity meters) was determined inappropriate for the estimation of TSS concentration in the very shallow subtropical estuarine system. x Table of Contents Title ............................................................................................................................ page Declaration ....................................................................................................................... i Acknowledgements........................................................................................................ iii List of Publications ....................................................................................................... vii Abstract