AbstractThe mechanism of onshore-offshore sediment transport and the process of beach profile evolution were studied through field investigations performed at Oarai Beach, Japan. The principal data set consists of twenty-four profile surveys taken at hourly intervals on each of two parallel lines spaced 10 m apart and of length 150 m. The lines extended from the backshore of the beach to a point on the sea bottom at a depth where no sand movement occurred. Simultaneous measurements of the waves and wave-induced currents were also made; the essential requirement of two-dimensionality was found to hold during the experiment. The profiles were used to calculate the net sediment transport rate on-offshore, and for an empirical eigenfunction analysis. A negative correlation was found between the transport direction (and resultant bottom change) and the mean sea level change. The sediment transport rate in the foreshore region was found to be proportional to the wave power, whereas outside the surf zone and near the breaker position it was proportional to the tractive force.
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