Comprehensive Field Study of Swash-Zone Processes. I: Experimental Design with Examples of Hydrodynamic and Sediment Transport Measurements
Publication: Journal of Waterway, Port, Coastal, and Ocean Engineering
Volume 140, Issue 1
Abstract
A comprehensive study of swash-zone hydrodynamics and sediment transport was conducted on a macrotidal beach in Perranporth, United Kingdom. The unique study is the first to simultaneously measure suspended sediment and sheet flow sediment concentrations, water depth, near-bed velocity profiles, and high-resolution swash surface and bed-level changes on a natural beach. Data collected during the study are used to quantify the vertical profile of cross-shore and alongshore velocities and the importance of sheet flow sediment processes in the swash zone. The swash-zone boundary layer for cross-shore velocities is observed to generally occur over at least the lower 0.06 m of the water column. Alongshore velocities are often the same order of magnitude as the cross-shore velocities and are dominant near cross-shore flow reversal. Flows are often logarithmic in profile, but the instantaneous nature of the measurements renders application of the logarithmic model difficult. When valid, the logarithmic model enabled cross-shore shear stress estimates of up to with maximum alongshore shear stress estimates of , further highlighting the potential importance of alongshore flows. Friction coefficient estimates, assuming a quadratic drag law, showed no statistical difference between onshore- and offshore-directed motion, with typical values of (). Sheet flow concentrations exceeded the maximum measured suspended sediment concentrations of approximately . Sediment loads in the sheet layer are up to 10 times larger than the sediment loads in the lower suspension layer. Simplified sheet flow sediment transport estimates are 3.6 times larger on average than those in the suspension layer. The latter two findings indicate the importance of sheet flow processes in the swash zone that are generally ignored.
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Acknowledgments
This material is based on work supported by National Science Foundation Grant No. OCE-0845004. Additional support for this work was provided by the University of Delaware, the Delaware Department of Natural Resources and Environmental Control, the Award for Global Research, Internships, and Performances for Graduate Students at the University of Delaware, the Natural Environmental Research Council (Grant No. NE/G007543/1), an Australian Research Council Discovery Project (No. DP110101176), and the US-UK Fulbright Commission. The authors thank B. Proença, L. Melo De Almeida, M. Sheridan, and P. Ganderton for assistance with the field measurements. Four reviewers provided insightful comments that improved the clarity of this manuscript.
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Published In
Journal of Waterway, Port, Coastal, and Ocean Engineering
Volume 140 • Issue 1 • January 2014
Pages: 14 - 28
Copyright
© 2014 American Society of Civil Engineers.
History
Received: Nov 29, 2012
Accepted: May 2, 2013
Published online: May 4, 2013
Published in print: Jan 1, 2014
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