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A model study of longshore transport rate Ametepe, Joseph Kwaku


Theory for across-shore transport as a function of beach slope and sediment size is extended to longshore transport. To test the theory, experimental measurements of longshore transport are required for a range of beach slopes and sediment sizes. Measurements were made of the sand transport caused by waves of different characteristics approaching the toe of an inclined model test beach of variable slope. The initial beach slope was 1 on 9. Three different tests sands of median diameters 0.50mm, 0.85mm and 2.0mm were used as beach material to investigate the probable influence of grain size on the longshore transport rate. Long crested waves generated in a constant depth of water travelled over the beach, shoaled and were refracted before breaking near the shoreline. The breaking action caused the sand to be transported along the shore in the direction of the longshore component of the wave energy flux. The laboratory measurements of the longshore transport are described, and it is shown that, for a given wave energy, transport increases with beach slope. Also, the distribution of the longshore sediment transport across the beach face is shown to be a function of beach slope and sediment size as higher transport rates were recorded for the coarser sands in zones of maximum wave energy dissipation. Based on the streampower approach and the radiation stress concepts, a theoretical model is developed for the estimation of the longshore transport as a function of incident wave height and direction, sediment characteristics and beach slope. The predictions of this model are shown to be in agreement with the experimental measurements.

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