An experimental study of changes of beach profile and mean grain size caused by tsunami-like waves

Abstract

Devastating tsunami waves can mobilize a substantial amount of coastal sediments and change the coastal morphology considerably. In this study, laboratory experiments were performed in a wave flume to investigate the changes of beach profile and mean grain size caused by tsunami-like waves that have a front similar to that of a solitary wave and an undulating tail following the wave front. A composite slope was constructed using a mixture of two sizes of sand. In addition to recording the wave rush-up and rush-down processes using video cameras, measurements were also made on water surface elevation, bed profile and the final size distribution of the sand mixture for three water depths. The results showed that sand suspension and erosion were caused mainly by sheet flows when water retreats from the beach, whereas the offshore sandbars, composed mainly of coarser sand, formed mainly from the run-down jumps caused by the collapsing of retreating water with waves in the undulating tail. The findings of this study have the potential to assist researchers in understanding nearshore tsunami flows from tsunami deposits.