Sorting and Selective Movement of Sediment on Coast With Steep Slope- Masurements and Prediction

Abstract

“Conveyer belts” carrying gravel and fine sand have developed on the Shimizu coast. After the construction of an L-shaped groin to protect the Hagoromo-no-matsu sandy beach located at the northern part of the Shimizu coast, these conveyer belts split into two, inducing longshore and offshore transport, because the seabed topography markedly changes and submarine canyons with a steep offshore slope develop immediately north of the L-groin. Coarse material is transported alongshore and fine material is discharged offshore. Material movement is investigated on the basis of bathymetric survey data and the depth distribution of the grain size of the seabed material. The effect of extending four breakwaters to control the movement of gravel and to stabilize the shoreline downcoast of the L-groin is predicted using the contour-line-change model. The optimum arrangement of breakwaters, along with beach nourishment, is numerically predicted.