2019 年 25 巻 p. 291-296
The 10th typhoon in 2016 that caused a massive flood disaster at Omoto river had several antecedent rainfalls. The river basin will be considerably saturated, which has led to exacerbating the flood disaster. Therefore, we should discuss the flood disaster occurred related to not only a short-time rainfall but also an antecedent rainfall. This paper describes the influence of antecedent rainfall on a flash flood in a mountainous river using a physical-based rainfall-runoff model that employed a fully-coupling simulation with surface-water flow and ground-water flow. The result of the simulation indicated that due to the infiltration of antecedent rainfall, a pressure rise has occurred across the basin, except the area directly under the river channel where the pressure has decreased. The groundwater flows toward the area of lower pressure head, which causes the ground water from all the basin to gather under the river channel. This clearly shows that antecedent rainfalls make ground-water easy to be pushed out to the surface and increase the flood-flow.
