STUDY ON INFLUENCE OF ROADS ON DEBRIS FLOWS DURING THE 2018 JULY HEAVY RAIN

抄録

 The heavy rain in July 2018 led to debris flows in mountainous residential areas, causing severe damage in western Japan. In Japan, mountainous streams where debris flows originate from the valley exit are often concealed by culverts upstream of the residential areas. Therefore, during the disasters that occurred in Kobe City and Hiroshima City due to the heavy rain in July 2018, culverts that existed upstream of the residential area were blocked by sediment, and debris flows moved down along the roads connected to the culverts. Furthermore, the slopes of the roads were steep, and debris flow in Kobe showed high mobility owing to the presence of fine sediment from the deposited granite sediment layer. Therefore, sediment extensively encroached into the residential areas. In this study, we aimed to analyze the disaster situation focusing on culverts and roads existing in residential areas based on field surveys. We conducted numerical simulations by applying a high-resolution digital elevation model (DEM) and digital surface model (DSM) to describe the disaster scenario. From simulation results, applying DSM in residential area described the disaster situation better than DEM. Furthermore, we considered disaster mitigation planning and proposed safe landuse in residential areas based on the simulation results.