Separation of shoreline change caused by cross-shore and longshore sediment transports

Shoreline change on Sendai Coast, Japan has been being measured every two weeks since 1993. The shoreline shows very complicated variation, though, there exists periods when two distinct patterns can be observed: one caused by cross-shore sediment transport and the other by longshore sediment movement. Thus, an empirical eigenfunction method is applied to the shoreline position data to detect these predominant modes. It is noted in the previous studies, this method is utilized for cross-shore beach profile, whereas in the present study, shoreline position is analyzed by means of this method. It is found that the measured shoreline data can be successfully separated into the modes caused by cross-shore and longshore sediment transports, accompanied with higher modes with negligibly smaller magnitude. The time-function of predominant modes shows close relationship with wave characteristics.