Rock Seawall in the Swash Zone to Reduce Wave Overtopping and Overwash of a Sand Beach

Abstract

Low rock structures have been constructed on some beaches to reduce storm-induced damage to backshore areas, but no method is available to design such structures. Four test series were conducted in a wave flume with a sand beach and a berm to compare the effectiveness of a narrow dune and a rock (stone) seawall placed on the foreshore in reducing wave overtopping and sand overwash. The incident irregular waves were kept approximately the same. The water level was raised to increase wave overtopping. The dune was effective in eliminating or reducing wave overtopping compared with the corresponding berm with no dune, but the narrow dune was destroyed easily as the water level was increased. The stone seawall reduced wave overtopping even after its deformation. A stone seawall buried inside a dune functioned like the dune initially and like the seawall after the sand on and inside the porous seawall was eroded by overtopping waves. An existing numerical model was extended to predict sand transport on and inside the porous structure in the swash zone.