Evaluation of Techniques for Flood Quantile Estimation in Canada
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Evaluation of Techniques for Flood Quantile Estimation in Canada by Shabnam Mostofi Zadeh A thesis presented to the University of Waterloo in fulfillment of the thesis requirement for the degree of Doctor of Philosophy in Civil Engineering Waterloo, Ontario, Canada, 2019 ©Shabnam Mostofi Zadeh 2019 Examining Committee Membership The following are the members who served on the Examining Committee for this thesis. The decision of the Examining Committee is by majority vote. External Examiner Veronica Webster Associate Professor Supervisor Donald H. Burn Professor Internal Member William K. Annable Associate Professor Internal Member Liping Fu Professor Internal-External Member Kumaraswamy Ponnambalam Professor ii Author’s Declaration This thesis consists of material all of which I authored or co-authored: see Statement of Contributions included in the thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. iii Statement of Contributions Chapter 2 was produced by Shabnam Mostofi Zadeh in collaboration with Donald Burn. Shabnam Mostofi Zadeh conceived of the presented idea, developed the models, carried out the experiments, and performed the computations under the supervision of Donald Burn. Donald Burn contributed to the interpretation of the results and provided input on the written manuscript. Chapter 3 was completed in collaboration with Martin Durocher, Postdoctoral Fellow of the Department of Civil and Environmental Engineering, University of Waterloo, Donald Burn of the Department of Civil and Environmental Engineering, University of Waterloo, and Fahim Ashkar, of University of Moncton. The original ideas in this work were jointly conceived by the group. Martin Durocher developed the methodology and performed the computations. Shabnam Mostofi Zadeh contributed the manual threshold selections for the dataset. Donald Burn supervised the project. All authors discussed the results and contributed to the final manuscript. Chapter 4 was again a collaborative work with the above-mentioned co-authors. Shabnam Mostofi Zadeh developed the proposed regional estimation models, performed the computations, and prepared the manuscript. Martin Durocher was instrumental in developing the automatic threshold selection method. Donald Burn supervised the research and assisted with analyzing the results. Fahim Ashkar provided feedback. Shabnam Mostofi Zadeh wrote the manuscript. All the co-authors provided comments and consultation on the manuscript. Chapter 5 was a collaborative work between Shabnam Mostofi Zadeh, Donald Burn and Nicole O’Brien. Shabnam Mostofi Zadeh planned the research, extracted the necessary dataset, performed most of the computations and analyzed the results. Donald Burn supervised the research and provided guidance and feedback. Nicole O’Brien carried out the simulations required for the field significance test. Shabnam Mostofi Zadeh wrote the manuscript with inputs from all co-authors. iv Abstract As one of the most destructive natural hazards, floods have a strong and devastating influence on various aspects of human society and the environment. Damages from floods can include property loss, destruction of infrastructure, loss of life, social and economic disruption from evacuations, and environmental degradation. Floods are inevitable natural events but their impacts on people and the environment can be reduced by putting mitigation measures in place. Underestimation of flood discharges will lead to increase flood risk, while overestimation will lead to unnecessary increased construction costs. Effective mitigation measures require a solid understanding of the frequency of floods. How frequently a flood event of a given magnitude may be expected to occur, known as frequency analysis, is of great importance. However, estimation of these frequencies is difficult since extreme events are by definition rare and the length of the recorded data for these events is often short. Thus, flood frequency analysis is essentially a problem of information scarcity. Methods of incorporating related samples of data to reach more accurate conclusions, known as regional (or pooled) frequency analysis, are well established and documented in the literature. In Canada, there has been limited research into a standard and formalized procedure for flood frequency analysis. There are no national guidelines for flood frequency analysis in Canada, unlike in other jurisdictions such as USA, UK, and Australia, and there is thus a lack of a standardized approach for flood quantile estimation. The research in this thesis investigates different approaches in flood frequency analysis to improve flood quantile estimation. This research develops and applies a standardized approach to estimate extreme flood quantiles in Canada. In the context of pooled flood frequency analysis, this work investigates different approaches for flood quantile estimation that consider annual maximum flow series and also peaks-over-threshold series, including techniques to extract events exceeding the threshold. Changes in extreme flow magnitude and frequency over time are also explored in a multi- temporal and multi-faceted approach. A pooling technique in the context of super regions was developed that improved quantile estimation in comparison to more traditional grouping methods. This work has led to the development of a semi- automated threshold selection method instrumental in extracting peaks-over-threshold series for a large dataset of gauging stations. The semi-automated threshold selection method was employed in developing an effective pooling method that promotes using peaks-over-threshold series in flood v frequency analysis. The proposed method generally provided better quantile estimates than those obtained by using annual maximum series. The thesis also investigates the nature of changes in flooding events in Canada and studies the characteristics of the observed temporal trends in the flow series. vi Acknowledgements I would like to begin by expressing my sincere appreciation to my supervisor, Dr. Don Burn, whose support, advice, and encouragement has helped me step forward throughout my program. I am very fortunate to be able to learn from such an accomplished researcher and distinguished supervisor. I am sincerely thankful for all his contributions of time, support and kindness throughout my time at the University of Waterloo. I am deeply grateful for my amazing research collaborators. Special thanks goes to Martin Durocher, Fahim Ashkar, and Nicole O’Brien for their wonderful advice, support, and friendship. They have all taught me so much about the field of statistical analysis throughout my research. I am also thankful to FloodNet for funding this research and providing me with this amazing opportunity to contribute to the field of Water Resources in Canada. It is my pleasure to thank my defence committee members, Dr. Veronica Webster from Michigan Technological University, Dr. William Annable, Dr. Liping Fu, and Dr. Kumaraswamy Ponnambalam from the University of Waterloo. During my PhD program at University of Waterloo, I was honored to receive numerous awards, Queen Elizabeth II Graduate Scholarship, Ontario Graduate Scholarship, University of Waterloo President’s Graduate Scholarship, AECOM Graduate Scholarship in Water Research, Dr. T.E. Unny Memorial Award, Dr. Erlane F. Soares Scholarship in Civil Engineering, and Provost Doctoral Entrance Award, which are hereby acknowledged. I wish to thank the Department of Civil and Environmental Engineering staff who have helped me in many ways during my studies. I’d additionally like to acknowledge my Master’s supervisor, Dr. Leonard Lye, for being an amazing mentor and providing me with so much support over the past 10 years. My gratitude goes to my friends both in Waterloo and St. John’s without whom my time would have not been filled with wonderful and enjoyable moments that we shared together. Last but certainly not least, my warmest gratitude goes to my family. I would not be anywhere near where I am today without them all believing in me. vii Dedication I dedicate this thesis first and foremost, to my beloved husband, Vandad for his unconditional love, helping me to find and realize my potential, and support me throughout this journey. I also dedicate this thesis, to my loving parents who have been a source of encouragement and inspiration to me throughout my life. viii Table of Contents Examining Committee Membership ....................................................................................................... ii Author’s Declaration ............................................................................................................................. iii Statement of Contributions .................................................................................................................... iv Abstract .................................................................................................................................................. v Acknowledgements .............................................................................................................................. vii Dedication ........................................................................................................................................... viii Table of Contents .................................................................................................................................