A field investigation was conducted for sand movement in the Tenryu-Enshunada watershed. Sediment samples on the coast and the riverbed were collected in a wide area including in the trench excavated at the old riverbed, for which mineral analysis based on magnetism and Optically Stimulated Luminescence measurements were applied. The ratio of magnetic and non-magnetic particles was found to be highly correlated with the geology of surface sediments. The spatial distribution of non-magnetic particles represented by quartz and feldspar enriched in the upstream geology, as well as the similarity in OSL intensities for the present and the past riverbed samples consistently supported a significant decrease in sediment supply from the upstream region of dams.