EFFECT OF SAND BYPASSING AT SAKUMA DAM IN TENRYU RIVER AS A MEASURE AGAINST EROSION OF TENRYU RIVER DELTA COAST

The long-term evolution of the Tenryu River delta associated with sand bypassing at several dams is investigated using the contour-line-change model considering the change in grain size. The effect of the increase in sediment yield from the river mouth on the nearby coasts is numerically predicted. When the sediment yield is artificially increased, the supplied sediment is mainly deposited around the river mouth, resulting in a large shoreline advance, but it takes a longer time for a sandy beach far from the river mouth to recover. Another measure, such as sand bypassing of the coast, is required to recover sandy beaches downcoast.