Post-seismic Surface Processes in the Zoumaling Gully in the Qingping Area, Southwestern China: Landslide, Debris-flow and Sediment Delivery

Abstract

The Zoumaling Gully locates about 80 km to the northeast of the epicenter of the M8.0 Wenchuan Earthquake, with the earthquake rupture, Yingxiu-Beichuan fault, running through the left bank of the gully. Huge amounts of co-seismic landslide debris were presented on the hillslopes and channels. The Zoumaling Gully was once a gingko scenic park where soil and water were conserved well and no large mass movement had occurred prior to the Wenchuan Earthquake in recent tens of years. Regarding that the surface processes in the Zoumaling Gully is totally different before and after the Wenchuan Earthquake, the Zoumaling Gully was selected as an example in this present study to examine the impact of earthquake on subsequent sediment yield and delivery. Field observations from May 2008 to May 2011 were conducted to record the post-seismic landslide and debris flow activities. The influencing factors of the erosion and deposition on the surface of the gully were analyzed, in order to provide evidences in supporting the reconstruction planning in the earthquake-affected area. Special attention was paid to the debris flow events occurred in the years of 2008 and 2010. Comparative analysis of the events revealed that the mean gradient of main channel and sub-channel and the rainfall intensity played important roles in the transportation of debris from sub-channel, which resulted in sediment storing in the main channel or sediment transporting to the inhabited alluvial fans and the Mianyuan River to form a debris dam and produce inundation.