Sediment transport and shoreline erosion induced by bichromatic waves with varying group period

Abstract

In the present paper, large scale experimental data are presented showing sediment transport and beach profile evolution at the inner surf zone, close to the shoreline. Four different bichromatic wave conditions have been generated characterized by a similar energy content but varying the wave group period (frequency bandwidth). The differences in the shoreline evolution and associated sediment transport are explained from the differences in the wave group period. It has been shown that increasing the wave group period promotes a seaward horizontal displacement in the shoreline erosion pattern. The inner surf zone shows larger erosion for increasing wave group periods. However at the swash zone larger wave group periods show a berm located further seaward with a relatively less shoreline retreat. Differences in the beach profile evolution are explained from the bandwidth influence in the propagation of wave groups and associated long wave. Larger wave group periods showed a progressive long wave pattern with the associated long wave out of phase with the wave group envelope. This resulted in negative long-wave induced sediment transport within the inner surf zone. Reduced wave group periods have shown a standing pattern that resulted in long wave motions in and out of phase with the wave group envelope depending on the cross-shore location. Within the inner surf zone this resulted in mostly positive long wave induced sediment transport for reduced wave group periods. It was also shown that the long wave induced sediment transport represented on average 18% of the total mobilized sediment transport.