Effects of Spatial Scales on Runoff / Sediment Transport in Mountain Catchments (2) -Results from Intensively Studied Catchments

Abstract

　Findings for spatial patterns of runoff and sediment transport at selected observation sites were summarized to elucidate processes controlling scale dependence and spatial heterogeneity of their catchment areas. We selected Fudoji and Kiryu watersheds in Shiga for runoff generation and Tanzawa in Kanagawa and Saru watersheds in Hokkaido for sediment transport. Regarding runoff generation, variation of concentration of specific chemical species (i.e. silica) suggested various flow paths from weathered bedrock layer to soil layer in small catchments, although variation tapered with increased catchment area because of the mixing of several flow components. Sediment transport also varied spatially depending on the catchment characteristics. Variation tapered with increased catchment area. Moreover, increased storage components and decreased ratios of sediment source areas to the total catchment area for larger drainage areas decreased the sediment transport with catchment areas in some catchments. Landscape legacies of sediment supply, storage, and transport can contribute to increased sediment yields in larger catchments.