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Remote Measurement and Analysis of Shallow Water Breaking Wave Characteristics

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Remote Measurement and Analysis of Shallow Water Breaking Wave Characteristics by Bryson R.D. Robertson A Thesis presented to The University of Guelph In partial fulfilment of requirements for the degree of Doctor of Philosophy in Engineering Guelph, Ontario, Canada © Bryson Robertson, September, 2013 ABSTRACT REMOTE MEASUREMENT AND THE ANALYSIS OF SHALLOW WATER BREAKING WAVE CHARACTERISTICS Bryson R.D. Robertson Advisor: University of Guelph, 2013 Dr. Kevin Hall This thesis is an investigation of one of the most important elements in coastal engineering design; shallow water breaking waves. Shallow water waves create large impact forces on coastal structures, drive sediment transport, regulate a number of biophysical and air-sea chemical processes, and ultimately control coastal morphology and storm inundation. The value of accurate measurements and prediction systems for breaking waves cannot be overstated - it is paramount to understanding the drivers of coastal processes, engineering design and hazard prediction. A detailed review of key original empirical work is presented in this thesis to give a historical perspective of wave breaking research and identify avenues yet to be explored. The majority of the published relationships were semi-empirically extracted from scaled laboratory tests or limited field investigations. Traditional field investigation methods generally suffer from low spatial resolution data, high researcher safety risks and exorbitant costs. This study presents a precise, robust and low cost method to extract all relevant breaking wave properties from irregular waves, using simple consumer digital camcorder and global positioning system (total cost: ~ $350 USD). The collective understanding of wave breaking characteristics is continually hampered by a lack of consistent definitions and measurement techniques for determining breaking, breaking depth and effective seafloor slope. In this detailed study, the dominant published definitions for the breaking depth and effective seafloor slope are compared, their reliability tested and the best practices suggested. A novel method of calculating the breaking depth, corrected for optical wave trough water level variations, displayed the lowest variability and was determined to best define the effective breaking depth. A newly presented effective seafloor slope definition, based on individual wavelength to depth ratios, increased predictive ability over previous seafloor slope extraction methods. Finally, an optimized breaking wave height prediction method finds a root mean square relative error of just 1.7 % within the ranges of measured dataset. Irregular waves investigated on an individual wave basis are shown to follow regular wave breaker height and depth prediction methods. Investigations into plunging breaker “intensity” using wave vortex geometric parameters have been ongoing for 50 years with limited success. Previously published works, based on regular wave flume results or solitary wave theory, present contradictory results and conclusions. This thesis investigates the predictability of vortex parameters and validity of using vortex parameters as indicators of breaking intensity. Detailed analysis determined that vortex parameters cannot be accurately predicted and are not suggested as a possible indicator of breaking intensity. Through this study, numerous innovative measurement methods and wave definitions were presented, defended and shown to increase our understanding of shallow water break events. The unique and highly detailed dataset of irregular breaking wave conditions allowed for unparalleled investigations into shallow water breaking waves. Acknowledgements Firstly, I would like to would like to express my sincere gratitude to Dr. Kevin Hall from University of Guelph for believing in me, inspiring me to research breaking waves and enabling me to work with so many incredible people. Without his continual support of this project, his technical expertise and ability to challenge me to work to my highest potential, this thesis would never have been possible. Considerable thanks are also extended to my advising committee members of Dr. Richard Zytner and Dr. Ioan Nistor for their practical advice, constructive critiques and enlightening reviews of continual draft documents. I would also like to thank Dr. Curt Storlazzi of the United States Geological Survey for vouching for an unknown Canadian research student, instilling proper research techniques in me and opening my eyes to the opportunities available to scientific researchers. Also thanks to Dr. Bradley Buckham at the University of Victoria for opening up short term graduate space for me and not evicting me after 16 months of occupation. The undying humour and encouraging advice from both Ryan Robertson and Hugh Patterson, while doing remote school work from the cockpit of Khulula, kept me laughing and inspired to follow through on this dream. To my wife, Jessica Robertson, for continually believing in me and encouraging me to achieve beyond what I thought was possible – thank you. Finally, to my parents, Mike and Diana Robertson, thank you for instilling in me a desire to learn, explore and understand. You taught me to work hard for what I want, to ask questions and to always follow through on worthy tasks. Your support and encouragement was been unconditional and I dedicate this thesis to you. iv Table of Contents REMOTE MEASUREMENT AND ANALYSIS OF SHALLOW WATER WAVE BREAKING CHARACTERISTICS ........................................................................... ERROR! BOOKMARK NOT DEFINED. ABSTRACT ........................................................................................................................................................ IV ACKNOWLEDGEMENTS ................................................................................................................................ IV LIST OF FIGURES ............................................................................................................................................ IX LIST OF TABLES............................................................................................................................................ XII LIST OF SYMBOLS ....................................................................................................................................... XIII 1 INTRODUCTION ........................................................................................................................................ 1 1.1 BACKGROUND AND RATIONALE .............................................................................................................. 1 1.2 EXPERIMENTAL OBJECTIVES AND APPROACH .......................................................................................... 3 1.3 NOVELTY OF STUDY ............................................................................................................................... 5 1.4 THESIS OUTLINE .................................................................................................................................... 5 1.5 LIST OF LITERATURE PERTAINING TO CURRENT THESIS ........................................................................... 6 2 WAVE THEORY BACKGROUND AND REVIEW .................................................................................. 7 2.1 WAVE GENERATION AND PROPAGATION ................................................................................................. 7 2.1.1 Airy Wave Theory .............................................................................................................................. 7 2.1.2 Non- Linear Wave Theories ............................................................................................................... 9 2.2 REGULAR VS . IRREGULAR WAVES ......................................................................................................... 15 2.3 SHALLOW WATER WAVE TRANSFORMATIONS ....................................................................................... 16 2.3.1 Wave Refraction .............................................................................................................................. 17 2.3.2 Wave Breaking ................................................................................................................................ 19 2.4 SURF SIMILARITY PARAMETERS ............................................................................................................ 19 2.5 WAVE BREAKING VORTEX RATIO ......................................................................................................... 20 2.6 BREAKING WAVE PARAMETER DEFINITION VARIANCE .......................................................................... 22 2.7 LABORATORY SCALING EFFECTS .......................................................................................................... 24 3 REVIEW OF BREAKING WAVE CHARACTERISTIC PREDICTORS .............................................. 26 3.1 BREAKING DEPTH INDEX ...................................................................................................................... 26 3.1.1 Regular Waves Breaking on Plane Beaches...................................................................................... 26 3.1.2 Regular Waves Breaking on Barred Slopes ...................................................................................... 39 3.1.3 Irregular Waves Breaking On Linear, Emergent Slopes ...................................................................
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