Longshore Sediment Flux in Water Column and across Surf Zone

Streamer sediment traps were used to measure the distribution of longshore sediment flux in the surf zone at 29 locations along the southeast coast of the United States and the Gulf coast of Florida. Measurements were conducted on both barred and nonbarred coasts under low-wave energy conditions. Results indicate that longshore sediment flux decreases logarithmically upward in the water column throughout the surf zone, and the rate of upward decrease is largest in the trough and smallest in the swash due to stronger mixing energy in the swash. Six types of cross-shore distribution patterns of longshore sediment transport (LST) were found. These six distribution patterns are controlled by nearshore morphology, breaker type, and energy dissipation pattern. For low-wave energy coasts, the swash (nonbarred coast) and inner surf (barred coast) zones contain significant contributions to the longshore sediment transport rate. The cross-shore distribution pattern of the longshore sediment transport rate along nonbarred coasts was well reproduced using energy-dissipation and shear-stress approaches developed mainly from laboratory studies.