DYNAMICS CHARACTER AND RIVER-BLOCKING ANALYSIS OF NARROW-STEEP CHANNELS DEBRIS FLOW IN WENCHUAN EARTHQUAKE REGION——ILLUSTRATED WITH CASE OF MOZI GULLY ALONG DUWEN FREEWAY

The debris flow with narrow-steep channels is very common in gully debris flow in Wenchuan earthquake region. High longitudinal slope and narrow average width of the gully and little drainage basin area are observed in this kind of debris flows. Thus, the debris flows with large scale is easily happened due to the quickly converge of the rainfall in earthquake area. In particular, extra-large group debris flows occurred on July 10, 2013 along Duwen freeway in Sichuan province. This paper concentrates on the phenomenon of the impaction, burying, blockage of Duwen freeway and Minjiang River caused by the debris flow. Through the field investigation of the debris flows, the formation conditions and development characteristics are identified. Using of CFX hydrodynamic calculation software, a simulation of the dynamical process of narrow-steep channels featured debris flow during 50-year storm conditions is set up. The paper makes a prediction of the hazardous region, evaluates the destructive effects on the Duwen freeway, Minjiang River and residents of settlements, which can provide the evidence of the prevention measures design of the debris flow.