Long-Period Wave Propagation and its Influence on Sediment Transport Over a Typical Beach in West Africa

Abstract The dominant wave in the west coast of Africa is bimodal spectrum wave consisting largely of long-period swell, where the spectral peak period is large (Tp = 8∼22s). The speed of long-period swell is also great, so the interaction mechanism of long-period wave with seabed is very complicated, which causes strong sediment transport and dramatic beach evolution. Therefore, the water-sediment movement characteristics are very different from those along the coast of China. However, there are few studies on the hydrodynamic processes in West Africa, and the propagation and deformation law of this kind of low frequency swell in the nearshore area and its influence on sediment transport and beach evolution are still unclear, which has caused serious problems to the design and construction of overseas projects, and needs to be studied urgently. In this paper, according to the characteristics of the west coast of Africa, the typical beach of Benin Bay is selected to establish a physical model test of beach profile, and the shallow water deformation and breaking of waves, the response characteristics of pore water pressure and the changes of nearshore topography are studied. In the experiment, two-peak spectra wave groups and long-period regular wave groups with different incident conditions were set up. Wave height meter, Particle Image Velocimetry (PIV) technology, pore water pressure sensor array and Sony Alpha 3 high-speed camera were used to observe the changes of free liquid surface, boundary layer velocity, pore water pressure gradient and nearshore topography during wave propagation. This study reveals the evolution of wave propagation and sediment transport mechanism under long-period waves in the West African coast, and the results can provide scientific and theoretical basis for beach protection and restoration in Benin sea area.