Abstract
The debris flow disasters in Hiroshima City on 20 August 2014 were surveyed via Unmanned Aerial Vehicle photography (UAV) and Structure from Motion photogrammetry (SfM) to measure sediment deposition volume and to reveal the characteristics of damage to buildings and of geology. The average flow path in areas of human casualties was smaller than that in areas of building damage. Most casualties were concentrated within an average of 132 m from the fan apex of each debris flow. The average flow path in areas of building damage was much longer on granite area than on hornfels area. On hornfels area, buildings stopped debris flow, but on granite area, fine particles continued downstream through gaps in buildings. These results show that the reach of debris flow in this event was the same as or less than the topographical development range of the alluvial cone.
