Characteristics and mechanism of Debris-Flow Surges at Jiangjia Ravine

Abstract

Debris Flows in nature, for example at Jiangjia Ravine, were often observed moving in the form of intermittent surges which is considered as a kind of wave that is termed as roll wave in this paper. Spatial and temporal characteristics of the roll waves at Jiangjia, as well as their separation and superposition were described in details. First-arrived waves were observed to smooth rough bed at the gentle middle reach and produce a residual layer on which a sequent wave can move with steady pro le and high velocity. The data measured by the Dongchuan Debris Flow Observation and Research Station shows the waves are not periodic and a kind of supercritical flow which only propagates downstream. Furthermore, it is observed that there are two kinds of wave profile, linear and non-linear, for the same debris-flow surge in Lagrange and Euler reference frames. A power relationship between the depth-averaged velocity and flow-depth of the surges is inferred from the different pro le functions in the two frames. Finally, it was proposed that mass exchange between the residual layer and moving wave reduces frictional resistance and keeps the wave high-speed.