Subsurface discharge and suspended sediment yield interactions in a valley head of a small forested watershed

Sediment hield caused by hydraulic agents is believed to be one of the most important geomorphic processes in headwaters. Observations of shallow groundwater levels and suspended sediment yield were used to develop relationships between subsurface discharge and sediment movement in a valley head of a small forested watershed in Hokkaido, northern Japan. Drainage capacity of the soil was closely correlated with subsurface soil movement in the valley head. An increase in subsurface discharge associated with an increase in the drainage capacity of the soil depended heavily on the discharge of fine-grained particles originating from the soil. Clogging created by the fine-grained particles in the soil caused a decrease in subsurface discharge associated with the decline in the drainage capacity. In addition, neither the drainage capacity of the soil nor subsurface discharge changed because of the sediment unavailability within the subsurface flow system. Accordingly, as shown by the changes in the drainage capacity of the sedimentary soil, subsurface discharge and suspended sediment yield from the valley head showed strong interactions.