土石流の流動特性・材料特性と規模-焼岳上々堀沢の土石流-

Abstract

Horizontal velocity profile, concentration of gravel and gravel-size distribution were ob-tained from the visual data of debris flow at the field observation site of the Kamikamihori valleyon the eastern slope of Mount Yakedake, in order to make clear the flow characteristics and thesize characteristics of the gravel in the flow. Three typical surface-velocity distribution, one witha plug flow transversely in the central part of the flow, the smooth distribution with a horizontalshear, and the highly turbulent one, were found in debris flows. The mobility factor, which wasdefined as the ratio of the surface velocity, to the friction velocity of the flow, was inversely cor-relative with the content of gravel. In case of a successive occurrence of debris flow surge, con-centration of gravel in the frontal part of the surge had a tendency to decrease one after another.There was a close correlation between the size-distribution quantities of gravel and the flowscale, while the diameter of the largest boulder in each flow was nearly equal to its maximumflow depth.