Abstract
Field observations and measurements of debris flows were carried out at three locations on Mt Unzen-Hugendake in 1992 and 1993. Two of the instrumented study sites were a downstream reach of the Mizunashi River, which are 12m and 25.1m wide and have an average slope of about 0.05 and 0.025, respectively. The other was a downstream reach of the Nakao River, which is 7.2m wide and have an average slope of about 0.025. Radio current-meter and ultrasonic water level gauge were used to obtain surface velocity, depth and discharge for the several flows.
The value of nondimensional surface velocity was found us/u*=5-10. Peak discharge was found Q=347m3/sec at the Mizunashi River and Q=57m3/sec at the Nakao River.
