COMPARISON OF ROCK SEAWALL AND DUNE FOR STORM DAMAGE REDUCTION

Four test series consisting of 14 tests and 140 runs (each run lasted 400 s) were conducted in a wave flume with a sand beach and a berm in order to compare the effectiveness of a 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 for all the runs. The water level was increased to create dune erosion and crest lowering as well as stone displacement. The dune was effective in eliminating or reducing wave overtopping and overwash in comparison to 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 and overwash even after it was damaged moderately. A stone seawall buried inside a dune was examined in the last test series. The buried seawall functioned like the dune initially and like the seawall after the sand on the seawall was eroded by overtopping waves. The buried seawall combines the aesthetics of the dune and the robustness of the stone seawall.