2002 Volume 46 Pages 1199-1204
Many river disasters took place along the Yukiya River reach in Karumai-cho of Iwate Prefecture due to heavy rain in October 1999. Actual disaster conditions were observed through field surveys and the mechanisms and causes were analyzed by comparative investigations of aerial photos taken before and after the flood. Two distinctive disasters occurred along the reach. The first is the disaster at flooding areas. The surface of the ground near eroded riverbanks was scoured and sands and gravels were carried away. This debris deposited widely on downstream areas. The returning flow of inundated water to the river channel destroyed bank protection works at the downstream reach of the flooding area. The second is the flooding due to the blockage of flood flow by drift timber. Drift timber flowed down mainly from eroded side banks of low-water channels and stayed upstream of a bridge.
