The Development and Evolution of the Burdekin River Estuary Freshwater Plume During Cyclone Debbie (2017)
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The development and evolution of the Burdekin River estuary freshwater plume during Cyclone Debbie (2017) Yuanchi Xiao A thesis in fulfilment of the requirements for the degree of Master of Philosophy School of Physical, Environmental and Mathematical Sciences The University of New South Wales Canberra, ACT, 2600, Australia August 2018 THE UNIVERSITY OF NEW SOUTH WALES Thesis/Dissertation Sheet Surname or Family name: Xiao First name: Yuanchi Other name/s: Abbreviation for degree as given in the University calendar: MPhil School: School of Physical Environmental and Faculty: The University of New South Wales Mathematical Sciences Canberra Title: The development and evolution of the Burdekin River estuary freshwater plume during Cyclone Debbie (2017) Abstract 350 words maximum: (PLEASE TYPE) This thesis investigates the plume morphology and dynamics prior to and after the landfall of Cyclone Debbie (2017). The heavy rainfall and flooding produced a large buoyant coastal current, which moved southward after the cyclone made landfall then advected northward with the prevailing southerly wind. The plume is simulated using the eReef GBR1 1-km model and a passive tracer is used to investigate the plume behaviour. Based on the concentration of river tracers from the Burdekin River, the plume propagated over 100 km to the north during the 23 days after the cyclone made landfall. Statistical analysis indicates that the longshore wind stress, x , is the dominant forcing for the freshwater plume from the Burdekin River. Under weak downwelling wind forcing (-0.1 Pa < < 0 Pa), the plume thickness is sensitive to river discharge and tides. With stronger downwelling wind forcing ( <= -0.1 Pa), vertical mixing is generated, the plume is restricted to the coast, and high river discharge affects the thickness of the plume, but not its width. After Cyclone Debbie made landfall, upwelling winds developed, and the freshwater plume reversed direction from northward to southward most likely due to the influence of the cyclonic northerly wind as well as the ambient current and topography. Based on an Empirical Orthogonal Function (EOF) analysis, the cyclone-induced river discharge is found to be the major cause for surface salinity variation with a lag time equal to 17 hours. In summary, this thesis highlights and compares the influence of both wind and river discharge on the river plume during the passage of cyclone and its analysis method for the river plume can be used in other case studies. Declaration relating to disposition of project thesis/dissertation I hereby grant to the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or in part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all property rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstracts International (this is applicable to doctoral theses only). 29/08/2018 ……………………………………………… ……………………………………..…… ……….……………………... …………… ………… …….… Signature Witness Signature Date The University recognises that there may be exceptional circumstances requiring restrictions on copying or conditions on use. Requests for restriction for a period of up to 2 years must be made in writing. Requests for a longer period of restriction may be considered in exceptional circumstances and require the approval of the Dean of Graduate Research. FOR OFFICE USE ONLY Date of completion of requirements for Award: i INCLUSION OF PUBLICATIONS STATEMENT UNSW is supportive of candidates publishing their research results during their candidature as detailed in the UNSW Thesis Examination Procedure. Publications can be used in their thesis in lieu of a Chapter if: The student contributed greater than 50% of the content in the publication and is the “primary author”, ie. the student was responsible primarily for the planning, execution and preparation of the work for publication The student has approval to include the publication in their thesis in lieu of a Chapter from their supervisor and Postgraduate Coordinator. The publication is not subject to any obligations or contractual agreements with a third party that would constrain its inclusion in the thesis Please indicate whether this thesis contains published material or not. This thesis contains no publications, either published or submitted for publication ☐ (if this box is checked, you may delete all the material on page 2) Some of the work described in this thesis has been published and it has been documented in the relevant Chapters with acknowledgement (if this box is ☐ checked, you may delete all the material on page 2) This thesis has publications (either published or submitted for publication) ☒ incorporated into it in lieu of a chapter and the details are presented below CANDIDATE’S DECLARATION I declare that: I have complied with the Thesis Examination Procedure where I have used a publication in lieu of a Chapter, the listed publication(s) below meet(s) the requirements to be included in the thesis. Name Signature Date (dd/mm/yy) Yuanchi Xiao 29/08/2018 Postgraduate Coordinator’s Declaration (to be filled in where publications are used in lieu of Chapters) I declare that: the information below is accurate where listed publication(s) have been used in lieu of Chapter(s), their use complies with the Thesis Examination Procedure the minimum requirements for the format of the thesis have been met. ii Originality Statement I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is acknowledged. Signed ……………………………………………...........……………… Date ……………………………………………..………….................29/08/2018 Yuanchi Xiao August 2018 iii Copyright Statement I hereby grant the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstract International (this is applicable to doctoral theses only). I have either used no substantial portions of copyright material in my thesis or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restriction of the digital copy of my thesis or dissertation. Signed ……………………………………………...........……………… Date ……………………………………………..………….................29/08/2018 iv Authenticity Statement I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digital format. Signed ……………………………………………...........……………… Date ……………………………………………..………….................29/08/2018 v Abstract This thesis investigates the plume morphology and dynamics prior to and after the landfall of Cyclone Debbie (2017). The heavy rainfall and flooding produced a large buoyant coastal current, which moved southward after the cyclone made landfall then advected northward with the prevailing southerly wind. The plume is simulated using the eReef GBR1 1-km model and a passive tracer is used to investigate the plume behaviour. Based on the concentration of river tracers from the Burdekin River, the plume propagated over 100 km to the north during the 23 days after the cyclone made landfall. Statistical analysis indicates that the longshore wind stress, x , is the dominant forcing for the freshwater plume from the Burdekin River. Under weak downwelling wind forcing (-0.1 Pa < < 0 Pa), the plume thickness is sensitive to river discharge and tides. With stronger downwelling wind forcing ( <= -0.1 Pa), vertical mixing is generated, the plume is restricted to the coast, and high river discharge affects the thickness of the plume, but not its width. After Cyclone Debbie made landfall, upwelling winds developed, and the freshwater plume reversed direction from northward to southward most likely due to the influence of the cyclonic northerly wind as well as the ambient current and topography. Based on an Empirical Orthogonal Function (EOF) analysis, the cyclone-induced river discharge is found to be the major cause for surface salinity variation with a lag time equal to 17 hours. In summary, this thesis highlights and compares the influence of both wind and river discharge on the river plume during the passage of Cyclone Debbie and the methodology used to analyse the river plume can be used in other case studies. i Acknowledgement This thesis includes work carried out as an MPhil student majoring in Oceanography in the Sino-Australian Research Centre for Coastal Management (SARCCM), School of Physical, Environmental and Mathematical Sciences (PEMS) of the University of New South Wales (UNSW) at Canberra, Australia. Firstly, I am very grateful to my supervisor Prof. Xiao Hua Wang and Joint supervisor A/Prof Liz Ritchie-Tyo.