土石流の総合的観測 その3. 1976年焼岳上々堀沢

Abstract

Systematic observation was carried out on the eastern slope of Mt. Yakedake in JapanAlps, in order to study physical processes of debris flow and some special phenomena con-cerned with the flow. Each stage of the debris flow such as the occurrence, growing, flowing, retarding and deposition was the direct objective of the present observation. Hydrologicalproperties of slope surface were investigated in the source area of the debris flow by useof various methods of physical sounding, and by the stream gauging to examine the relationbetween the rainfall and occurrence of debris flow.In order to attain the above mentioned purpose, the synthetic observation system equippedwith many instruments was extended over the whole course of valley Kamikamihorizawa.The main results of this observation are as follows: (a) The continuous record of velocityand discharge of a specified debris flows were obtained. (b) Exact size distribution of largestones in the head of the debris flow was measured. ? Vibration of ground due to thepassage of the debris flow was measured, and it was revealed that the magnitude of acce-leration was so high that the vibration may affect the fluidization of deposits in the valleybed. (d) Changing features in valley bed profile caused with the occurrence of debris flowwere revealed by the survey carried out three times during the observation period. (e)About a half part of the source area has a small infiltration capacity, so that sufficient quantityof water and sediment can be supplied to the valley under a certain meteological conditions.