On the Shimizu coast, artificial headlands and L-type groin were built as a measure against beach erosion. After the construction of the L-type groin, fine sand accumulated on the seabed covered with gravel off L-type groin, causing damages in the fishing ground on a shallow seabed. Seabed sounding and sampling test of bed materials were carried out. The contour-line-change model was applied to the coast to study the mechanism. On this beach, a steep (gentle) slope covered with gravel (fine sand) develops in a zone shallower (deeper) than -4 m, and beach changes take place without strong mixing of bed materials. The change in grain size is implicitly considered as the difference in the equilibrium slope in these areas. Measured phenomena were well explained by the present modeling
