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The role of suspension events in cross-shore and longshore suspended sediment transport in the surf zone

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Abstract

Suspension of sand in the surf zone is intermittent. Especially striking in a time series of concentration are periods of intense suspension, suspension events, when the water column suspended sediment concentration is an order of magnitude greater than the mean concentration. The prevalence, timing, and contribution of suspension events to cross-shore and longshore suspended sediment transport are explored using field data collected in the inner half of the surf zone during a large storm at Duck, NC. Suspension events are defined as periods when the concentration is above a threshold. Events tended to occur during onshore flow under the wave crest, resulting in an onshore contribution to the suspended sediment transport. Even though large events occurred less than 10 percent of the total time, at some locations onshore transport associated with suspension events was greater than mean-current driven offshore-directed transport during non-event periods, causing the net suspended sediment transport to be onshore. Events and fluctuations in longshore velocity were not correlated. However, events did increase the longshore suspended sediment transport by approximately the amount they increase the mean concentration, which can be up to 35%. Because of the lack of correlation, the longshore suspended sediment transport can be modeled without considering the details of the intensity and time of events as the vertical integration of the product of the time-averaged longshore velocity and an event-augmented time-averaged concentration. However, to accurately model cross-shore suspended sediment transport, the timing and intensity of suspension events must be reproduced.

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Additional publication details

Publication type Conference Paper
Publication Subtype Conference Paper
Title The role of suspension events in cross-shore and longshore suspended sediment transport in the surf zone
Year Published 2015
Language English
Publisher World Scientific
Contributing office(s) Pacific Coastal and Marine Science Center
Larger Work Type Book
Larger Work Subtype Conference publication
Larger Work Title The Proceedings of the Coastal Sediments 2015
Conference Title Coastal Sediments 2015
Conference Location San Diego, CA
Conference Date May 11-15, 2015
Country United States
State North Carolina
City Duck