Field observations of the disastrous 11 July 2013 debris flows in Qipan gully, Wenchuan area, Southwestern China

Abstract

Debris flows, with their ability to rapidly erode and transport large amounts of materials, have the potential for massive destruction and is one of the most hazardous consequences of strong earthquakes. On July 11, 2013, a catastrophic debris flow was triggered by a rainstorm in Qipan gully, Wenchuan County, southwestern China. The debris flow transported more than one million m3 of sediment to the reconstructed residential area and generated a debris-dam that blocked the Minjiang River. This paper aims to describe the characteristics, rainfall condition, debris flow initiation and run-out. Field investigation and image interpretation indicate that abundant co-seismic landslides triggered by the Wenchuan earthquake hanging on steep slopes in the catchment. The debris flow was triggered by a rainfall with intensity of 6.4 mm/hr and lasted for 3 days, with cumulative antecedent rainfall reaches 110 mm. It is conclude that with high accumulated antecedent rainfall, the triggering rainfall intensity threshold could be lower for the debris flow occurrence. From our field observations, we suggest that the breaching of the landslide dams have played an important role in transporting of huge quantities of sediments to gully outlet and blocking the Minjiang River. .