Influence of debris flow on channel evolution

Abstract

Affected by the active plate motion, the upper Minjiang River develops more than 21 debris flow valleys. After the Wenchuan earthquake on May 12, 2008, the geohazards occur more frequently and seriously because of the increased debris source, and 9 debris flows blocked the mainstream. Based on the characteristics of debris-flow dams, model tests have been accomplished. Given the junction angle of 90°, influence of debris flow on channel evolution is discussed for different ow density, and discharge ratio and momentum ratio between debris flow and the mainstream water flow. The results show that there is a linear relationship between momentum ratio RM (ratio between momentum for flow in tributary and mainstream) and shrink ratio S (index de ned to describe the magnitude of channel shrink after in flow of debris) of mainstream, and also an exponential relationship between the ultimate average width Bm (index defined to describe the average width of river channel after dam failure) of mainstream and the coefficient of velocity variation Fv (ratio between velocity for flow in mainstream after dam failure and before its formation).