Cross-shore Structure of Longshore Currents During Duck94

Falk Feddersen, R.T. Guza, Steve Elgar, T.H.C. Herbers

Proceedings of the 1996 Coastal Engineering Conference


The cross-shore structure of the mean longshore current on a barred beach is investigated with observations from the Duck94 field experiment. Maxima of the hourly-averaged longshore current are most frequently located either slightly inshore of the bar crest or near the shoreline. At low tide the longshore current maxima are located closer to the bar crest, and the current is stronger and narrower than at high tide. The tidal cross-shore displacement of the longshore current maximum is qualitatively consistent with the observed radiation stress, Sxy although the maximum currents are displaced shoreward of the maximum Sxy gradients at both high and low tide. This spatial lag suggests that some mechanism (such as wave rollers) delays the transfer of momentum from waves to the mean flow. Bathymetric longshore inhomogeneities may also affect the cross-shore structure of the longshore current.

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