Estimation of Potential Sediment Yield by integrating USLE with GIS -A case study at Tenryu Watershed in Central Japan-

The Japanese archipelago has high potentiality in producing huge sediments due to its topographical and hydro-meteorological conditions. Of all, Tenryu basin, having its headwater sources in the highest mountain ranges, the Japanese Alps in Central Japan, is one of the highest sediment yield river. Frequent fluctuation of channel beds and deposition of huge sediments in the reservoirs have been a severe problem. In order to control flood and manage river system, an integrated management of entire watershed is considered to be a desirable strategy; therefore, estimation of potential sediment yield in a large watershed, has been an important issue. This study was attempted to estimate the sediment yield at eight sub-watersheds: Yokokawa, Katagiri, Matsukawa, Shintoyone, Minowa, Miwa, Koshibu and Misakubo watersheds of the Tenryu basin using USLE model incorporated with GIS techniques, and validated the estimated sediment yield with the actual sedimentation measured from their corresponding reservoirs. From the study, it was found that the variation of observed annual sedimentation at reservoirs has showed similar trend with the estimated USLE values within the studied watershed. This outcome suggests the reliability and adaptability of the USLE method that is integrated with GIS in estimating annual potential sediment yield in the large watershed having complex topography and geology.