Steep wave,turbulence, and sediment concentration statistics beneath a breaking wave field and their implications for sediment transport |
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| Authors: | Nicholas V Scott Tian-Jian Hsu Daniel Cox |
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| Institution: | 1. Civil and Coastal Engineering, University of Florida, Gainesville, FL 32611, USA;2. Center for Applied Coastal Research, Civil and Environmental Engineering, University of Delaware, Newark, DE 19716, USA;3. O. H. Hinsdale Wave Research Laboratory, Oregon State University, Corvallis, OR 97331, USA |
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| Abstract: | A new methodology based on wavelet analysis is used to estimate steep wave statistics under depth-limited conditions and the corresponding high concentration sediment statistics. Steep waves here are defined as wave crests within the wavelet transform exceeding a root mean square derived acceleration threshold. The method is applied to laboratory data obtained in a large-scale wave-flume experiment conducted in 2005 at Oregon State University's O. H. Hinsdale Wave Research Laboratory from an acoustic Doppler velocimeter and a fiber optic backscatter sensor array above a mobile sand bed. The steep wave and high concentration statistical results for the erosive condition suggest that sand suspensions are intermittent when a wave-breaking timescale (the ratio of breaking wave height and rms wave velocity) is used to detect the concurrence among steep wave, high velocity turbulent fluctuations, and sand concentration events near the bed. More importantly, at 1 cm above the bed, though the accretive case has more steep wave events, the erosive case has more steep waves and concurrent high concentration events, suggesting a more intense breaking wave process near the sensors. The use of a longer time window, based on the dominant wave period in the detection process of steep wave and high concentration events at 1 cm above the bed, does not change the resulting statistics for the erosive condition. However, increased percentages of high concentration events correlated with steep wave and high velocity turbulence events for the accretive condition are obtained. These increased percentages are conjectured to be due to advection of non-local turbulent events and sediment concentration peaks from upstream. |
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| Keywords: | Morlet wavelet transform Sediment transport Cross-shore transport Steep waves Turbulence Large wave-flume experiment |
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