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Remote Measurement and Analysis of Shallow Water Wave Breaking Characteristics

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Title: Remote Measurement and Analysis of Shallow Water Wave Breaking Characteristics
Author: Robertson, Bryson
Department: School of Engineering
Program: Engineering
Advisor: Hall, Kevin
Abstract: 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.
Date: 2013-09
Rights: Attribution-NonCommercial 2.5 Canada

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Attribution-NonCommercial 2.5 Canada Except where otherwise noted, this item's license is described as Attribution-NonCommercial 2.5 Canada