Abstract
　Big debris flows and many slope failures were caused by a heavy rainfall in Mt. Aso area, Kumamoto Prefecture on July 2, 1990. Bulky drifting woods were resulted from these in the Furue River, which is one of the branches of the Kuro River. The flood and bulky drifting woods caused a miserable disaster, which killed 8 persons and demolished about 150 houses. And 13 Sabo dams along the Furue River were destroyed by the debris flows.
　Through investigating the disaster, the following matters were verified. Most of the destroyed dams were constructed in Showa 30's. The destroyed dams have had defects within their own internal structures. Height increasing methods and reinforcement works of the front apron of the dam have had defects. The failure of the dams due to the debris flows began from the downstream side of the dam crown and propagated to the upper side. These failures were repeated and the dam was finally destroyed completely. Bulky drifting woods were caused by the riverside erosion by the debris flows and slope failures. And the failures of the dams themselves also had influences on the occurrence of drifting woods.
　From these results, construction of slit dams to hold the drifting woods, security of retarding basins, and check of the dams constructed in Showa 30's are proposed as a future countermeasure.

【キーワード】：集中豪雨，土石流，砂防ダム，流出土砂量
Key words: local severe rain, debris flow, Sabo dam, sediment yield

*熊本工業大学土木工学科
Department of Civil Engineering, Kumamoto Institute of Technology