MECHANISM AND CHARACTERISTICS ON DEBRIS FLOW HAZARDS IN YINCHANGGOU AREA TRIGGERED BY RAINSTORM ON AUGUST 18, 2012

A group of debris flow hazards occurred at Yinchanggou area on August 18,2012.This area was part of the epicenter region of Wenchuan earthquake. These debris flows greatly impacted the community of the Yinchanggou area and produced some casualties. This event also damaged many roads and other infrastructures. Debris flow hazards resulted from the coaction of the rainstorm and earthquake. Therefore,it is significant for better understanding of characters of debris flows to conduct the research on the mechanism in extreme seismic area. Field investigation and interpretations of aerial photographs were used to analyze variation of debris flow factors. This study demonstrates that loose mass generated by the collapse and landslides provided abundant materials for debris flows. The blockage of channel increased the scale of debris flow. Rainstorm like rapid triggering response pattern provided power for debris flow initiation. After discussing initiation,motion and deposition process,this study discovers that debris flows distributed like a band along fault and were very young. The trigger and control factors depend mainly on the rainfall condition. Besides,these hazards resulted from the coaction of debris flow itself and community.