Kana NAKATANI, Megumi KOSUGI, Yoshifumi SATOFUKA and Takahisa MIZUYAMA
Debris flows cause flooding and sediment deposition when they reach alluvial fan areas. In Japan, urban development has led to housing commonly being built in such areas. Therefore, in the event of a debris flow, the location of the housing seems to affect flooding and deposition. Due to the nature of the housing and the often steep topography of the areas in between, roads are generally located at lower elevations; during previous debris flow disasters, many cases have been reported where the flows moved down along these roads. In this study, we conducted disaster verification on the debris flow events that occurred in Hiroshima, Japan, in August 2014. Then we performed debris flow numerical simulations using the Hyper KANAKO system to determine the influence of housing and roads on the Hiroshima debris flow events. We performed the simulations with and without housing. The results show that the location of housing can explain the causes of the disaster. Considering the hazard area and evacuation procedure, it seems to be advisable to take the influence of housing into consideration. Furthermore, we conducted simulations by varying the width of the main road, because in a disaster situation, the main debris flow seems to move down along this road. In the simulation, we observed that the main debris flow moved along this road when the road was widened, while part of the flow spread laterally towards other roads when the main]road width was reduced.
Key wordsFDebris flow, alluvial fan area, houses, roads, numerical simulation, Hiroshima