Abstract
Toyohira River in a vicinity of Makomanai River confluence which is an alluvial fan head is the location where the riverbed has long been deformed actively. Decreasing sediment supply by dam constructions since 1907 and Sabo-dam constructions in 1954 and sediment runoff by large floods in the 1950s to 1970s led to bed degradation. Problems such as an insufficient depth of pier embedment and the revetment failure have been emerged. In this study, we analyzed sediment dynamics of Toyohira River basin using the materials and it showed the relationship with riverbed degradation. Furthermore, we redeveloped the sediment runoff model considering changes in watershed conditions into the previous model. The results suggest quantitatively that the relationship between the difference of sediment discharge ratio among the watersheds of mountain stream with Sabo-damand measured sediment volume in Moiwa's intakeweir.
