A DISCUSSION ON MECHANISM OF VISCOUS DEBRIS FLOW VIA SURFACE VELOCITY ANALYSIS

Abstract

The viscous debris flow occurs frequently in the southwest of China. This natural event inflict damage on people or property. For the purpose of mitigation planning, it need to elucidate the mechanism of viscous debris flow. And then, it is necessary to analyze the motion of it.
On July 24th, 1997, a viscous debris flow was recorded with a digital video camera in JiangJia Gully, Dongchuan City, Yunnan Province, China. These images were saved as files formatted as BMP by computer interface board. Since the absolute coordinates of targets which were near the channel were surveyed by an infrared-light distance meter, the distance of a pixel of images about motion of debris flow is estimated in x and y direction, respectively. A new image analysis method, the auto-correlation method, is used to analyze the surface velocity of debris flow.
In this paper, the two results of image analysis are shown: one is the mean surface velocity change of central of several surges, another is the change of surface velocity vector in a fixed cross section. According to these results and the field experiment, it could be concluded that viscous debris flow is a kind of complex flow. It is a turbulence in the front of a surge; in the middle of a surge, it could be considered as a kind of cohesive flow; and due to the cohesion or yield strength, the flow almost stops in the end of a surge.