COMPARISON OF STORM LONGSHORE TRANSPORT RATES TO PREDICTIONS

Herman C. Miller

Abstract


Longshore sediment transport (LST) is of primary importance to long-term shoreline changes and must be accounted for in most coastal designs. Predicting LST has been hampered by the lack of direct measurements during storm conditions against which the models can be calibrated. The Sensor Insertion System (SIS) developed at the US Army Corps of Engineers (USACE) Field Research Facility provides a way to directly measure LST during storms. The SIS was operated during the growth, peak, and waning stages of three storms between April, 1997 and February, 1998 in which the waves reached a maximum individual height of 5.6m. In up to 14 cross-shore locations, concentration and velocity measurements were made throughout the water column. These measurements were compared to total transport models of USACE 1984, Kamphius 1991, Kraus, et al. 1988, Walton 1980, and the cross-shore distribution model of Bodge and Dean 1987. The results show the storm measurements had a consistent pattern; rapidly increasing to a peak rate, then gradually decreasing during the waning stages of each storm. Cross-shore distributions of longshore flux tended to peak over the offshore bar and at the beach where wave dissipation caused high suspended sediment concentrations. These peaks were not co-located with maximum longshore currents, which tended to peak at mid-surf. The comparisons show that the models would benefit from comparison to the storm measurements.

Keywords


longshore transport; transport rate; storm; transport prediction

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