SYNTHETIC OBSERVATION ON DEBRIS FLOW Part 4. Observation at valley Kamikamihorizawa of Mt. Yakedake in 1977

Abstract

Observation of debris flow was carried out on the eastern slope of Mt. Yakedake in 1977, bythe use of new equipments, such as a vector rain gauge, new electrical ground water level gauges, fixed cameras hung in the air near valley bed, seismometers of buried type, debris samplers to trap50 liters of debris mixture and three speedometers of different types besides the instrumentationused in the former year. As there occurred only two small debris flows in this year, we could getfew dynamical data about the motion of debris flow. On the other hand, an intensive surveywas carried out concerning with the micromorphological processes in the valley bed and sourcearea.As the results of the above survey, we got the following knowledge related to debris flow; (a)subsurface structure of the slope in the source area with reference to permeability, (b) actualprecipitation on the slopes by vector rainfall, ? unit hydrograph for a small gully in the sourcearea, (d) the mechanism of depositional processes in the valley bed, and (e) the origin of rawmaterial in a debris flow by the particle size analysis.Observation of debris flow was carried out on the eastern slope of Mt. Yakedake in 1977, bythe use of new equipments, such as a vector rain gauge, new electrical ground water level gauges,fixed cameras hung in the air near valley bed, seismometers of buried type, debris samplers to trap50 liters of debris mixture and three speedometers of different types besides the instrumentationused in the former year. As there occurred only two small debris flows in this year, we could getfew dynamical data about the motion of debris flow. On the other hand, an intensive surveywas carried out concerning with the micromorphological processes in the valley bed and sourcearea.As the results of the above survey, we got the following knowledge related to debris flow; (a)subsurface structure of the slope in the source area with reference to permeability, (b) actualprecipitation on the slopes by vector rainfall, ? unit hydrograph for a small gully in the sourcearea, (d) the mechanism of depositional processes in the valley bed, and (e) the origin of rawmaterial in a debris flow by the particle size analysis