Foreshore morphodynamic changes in a bimodal sediment beach

This study intends to examine modifications of the foreshore related to beach profile recovery and the resulting depositional structures after the occurrence of storm events. The experiments were done in the "Concheiros do Albardao" region, located 10Km northward of the Hermenegildo balneary, in Southern Brazil. At both experiments, beach accretion was observed with larger changes recorded at the lower foreshore. During the "runs", significant grain size changes were recorded. A clear zonation in the surficial sediment distribution was noticed with finer, coarser and bimodal sediments located respectively at the upper, intermediate and lower portion of the foreshore. Sediment cores demonstrated laminations alternatively composed exclusively of quartz and carbonate sands or composed by a mixture of both. It appears that at the upper part of the beach rates of beach accretion were induced by moderate wave regime at lower water table levels. Morphological changes in the lower portions can be related to lower water table levels as well as higher turbulence caused by the colliding uprush and backwash.