In order to investigate the response of beach profiles to incident
waves, computations by the empirical eigenfunction analysis proposed
by Winant et al. are performed. The analysis of the data obtained
at Ajigaura Beach over three years from 1976 to 1979 indicates that
beach profile changes due to longshore and onshore-offshore sediment
transport are separable by the empirical eigenfunction method. The
beach profile changes due to longshore sediment transport has a time
lag of 12 weeks with respect to the change of wave direction at Ajigaura Beach. It was found theoretically that this time lag was due to
the sand waves propagating in the longshore direction. Regarding as
onshore-offshore sand transport, the second eigenfunction is associated
with the beach changes due to onshore-offshore sand transport caused
by the change of wave height.