土石流の総合的観測その5. 1978年焼岳上々堀沢における観測

Abstract

Direct observation of debris flow and various surveys concerning the phenomena accom-panied with debris flow were carried out on the eastern slope of Mt. Yakedake in 1978. Inexecution of the former, a synthetic observation system equipped with many instrumentationswas set in operation which had been devised and put to practical use till the last year.The latter mainly consists of three types of survey. In the source area of valley Kamikamihori, measurement of slope erosion and rill profile was frequently carried out besides the mete-orological and hydrological observations. In the channel reach, some measurements were alsofrequently held concerning with microgeomorphological processes in the valley bed.Special surveys on debris flow was started at the alluvial fan this year in order to studythe physical character of the debris flow in retarding and stopping stages and to investigatethe distinguishing feature of debris deposition caused with decrease in slope angle andseparation of water from debris. Recording of moving state of the debris flow with cameras, microtopographical survey on erosional and depositional effects, and particle size analysis ofdeposit were carried out near the intersection point at the fan.As the result, we have obtained the following knowledges; (a) correlation between rainfallvector and wind direction or wind velocity, (b) relationship between the locality of rainfalldistribution and occurrence of debris flow, ? relationship between rainfall intensity andcoefficient of runoff or infiltration capacity, (d) lateral inclination of the head part of debrisflow, (e) exact measurement on surface velocity of debris flow by use of spatial filterspeedometer, (f) frequency characteristics of the ground vibration attended with debris flow, (g) seasonal changes in the valley bed processes, (h) characteristic moving state as acollective fluid of debris flow at the fan, (I) comparison of erosional and depositonal featuresbetween debris flow and sand flow, and (j) relationship between particle size distribution ofdebris and depositional conditions.