ABSTRACT
This study is conducted to discuss the characteristics of active sediment transport processes in extreme flood hazards and investigate methodologies for numerical simulation of such hazards. Two flood disasters that recently occurred in Japan are investigated. They are characterized as a huge amount of sediment production from the mountains due to landslides and debris flows which carried a large amount of sediment to the downstream areas with the flood flow. They are also characterized by obvious sediment sorting within a short distance. In order to simulate these phenomena numerically, methodologies are proposed to compute bedload transport using a bedload formula with a sediment transport rate proportional to the 2.5th power of the non-dimensional tractive force. The numerical simulation found that the conditions of sediment supply from the upstream reaches need to be carefully determined to evaluate extreme flood hazards such as the ones investigated in this study.
