2018 Volume 24 Pages 433-438
By Typhoon Talas in 2011, the Iseki District in the Nachi River basin suffered great damage due to flooding. In this disaster, there was the blockage of the bridge by driftwood and the accumulation of big boulders in the Nachi River flowing down from the tributaries. In order to elucidate the mechanism of flooding, it is important to verify the impact by the driftwood and the big boulders.
First, using the topographic data, we investigated the places where the sediment and the driftwood were mainly deposited by the disaster. Second, the area including the Iseki district and the confluence of the Nachi River and the Kanayamatani River (The tributary of the Nachi River) were divided into meshes. Then, we investigated the length of the driftwood and the size of the big boulders for each mesh.
We found that the blockage of the bridge by the driftwood and the sedimentation of the big boulders in the Nachi River mainly caused the flood of the Iseki district.
