A model for predicting bathymetric and grain size changes considering equilibrium slopes corresponding to the composition of grain size and each grain size was applied to predict the beach changes on the Chigasakinaka coast. The cross-shore sorting of sand, in which the grain size gradually decreases with increasing depth, and the formation of a gradually changing longitudinal slope were reproduced well. The diffusion of colored sand with different grain sizes placed on the shoreline and at a depth of 4 m was predicted and compared with the results of a field observation using colored sand on the Chigasakinaka coast. Both results were in good agreement.
