Author(s): Shouma Ishikawa; Shuichi Kure; Ryuusei Yagi; Bambang Priyambodho
Keywords: Rainfall runoff simulation; Flood; Hazard evaluation; Toyama
Abstract: In Japan, typhoons and frontal rains cause severe water-related disasters almost annually, resulting in considerable damage to human life and property. Although multiple hazard and risk evaluations have been conducted in Japanese rivers, hazard evaluations of smaller rivers and tributaries managed by prefectures are unsatisfactory compared with those of the larger rivers managed by the national government. Several flood-related disasters occur in these small rivers because of insufficient data and risk analysis. This study primarily aims to evaluate the hazards and risks associated with all the rivers in Toyama Prefecture, Japan. In this study, a physical rainfall-runoff was utilized to evaluate flood inundation hazards in Toyama, Japan. For the rainfall runoff simulation, a physical distributed rainfall-runoff model was employed because it can simulate the hortonian overland flow in urban areas and the subsurface flow and saturation overland flow in mountainous areas. Flood inundations were simulated using input rainfall datasets, and the obtained results were compared based on a flood-vulnerability index of the rivers. The analysis showed that small rivers managed by the prefecture exhibited a shortage of capacity flows against large floods. These small rivers can easily be inundated when heavy rainfall occurs in the near future. Therefore, local residents need to be aware of this risk, and appropriate countermeasures should be adopted at the earliest.