Abstract
Sediment discharge generated from snowmelt was observed in the Ikushunbetsu River, Hokkaido (basin area: 60.0 km2) in April 1993. Continuous records of water discharge, Q and suspended sediment concentration, Cs exhibit synchronous time variations at a station along a river channel and a downstream increase in sediment discharge (Qs=Q·Cs) between two stations. The sediment suspended over 90 % of water depth consists of more than 95 wt.% of silt (3.91<d≤62.5 μm) and clay (d≤3.91 μm). Sources of the fine suspended sediment were identified by comparing grain size distributions of some sediment samples taken along the river channel, being supplemented by mineralogical analysis. It is concluded that the sediment discharge is generated by the fluvial erosion of weathered soils deposited on a side gorge slope, and the amount of eroding sediment is approximately proportional to the fluvial shear stress.
