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