Sediment Management Technique for Agricultural Watershed

Soil erosion and runoff have led to agricultural and environmental problems throughout the world. Therefore effective measures which can reduce sediment yield in the farmland are necessary. For the purpose, advanced sediment management technique is required. A study area is Nagura-river watershed, Ishigaki Island, Japan. GIS for sediment management in watershed was constructed. Consequently, multi-points observation was carried out at six points in the watershed. In these studies, a soil erosion and sediment runoff model was constructed and tested to verify their applicability in predicting sediment yield and sediment runoff. The calculated sediment runoff by the model was in approximate agreement with the observed. In the present application to the watershed sediment management, the authors carried out some case studies to choose proper combination of sediment yield reduction measures. The calculation has shown that sediment runoff at outlet of the watershed can be reduced by 12% if the measures about land deformation are taken into consideration. Another calculation has shown that sediment runoff can be reduced by 74% if the combination of measures about land deformation and about farming program is properly chosen.