Increased sediment discharge driven by heavy rainfall after Wenchuan earthquake: A case study in the upper reaches of the Min River, Sichuan, China

Abstract

The Wenchuan earthquake with magnitude 8.0 hit Longmen Mountain on May 12, 2008. The coseismic deformation changed the slope in an instant and caused massive outbreaks of landslides and debris flows, which altered the river transport system. The seismic landslides, debris flows and subsequent heavy rainfall and flooding increased sediment discharge. Data on sediment discharge, rainfall, landslides, and debris flows were collected in this study for 1980–2010 to describe the effects of the Wenchuan earthquake and post-earthquake heavy rainfall on the increase in sediment discharge in the upper reaches of the Min River. The relationship between precipitation, sediment discharge, landslides, and debris flows before and after the Wenchuan earthquake in the upper reaches of the Min River was analyzed. The variation trends of sediment discharge in the river basin before and after the earthquake were calculated quantitatively. The research results can be summarized as follows: (1) Sediment discharge increased by approximately 30% due to coseismic uplift, coseismic landslides, and debris flows after the Wenchuan earthquake. (2) The sediment discharge caused by heavy rainfall after the earthquake was 1.75 times larger than before the earthquake. The percentage contribution of the sediment yield of debris flows induced by heavy rainfall after the earthquake to the increase in sediment discharge was 34.54%. (3) The heavy rainfall zone basically coincided with the earthquake fault zone and the seismic landslide zone. Therefore, there was a positive-feedback relationship between the increase of sediment discharge and heavy rainfall after the Wenchuan earthquake. (4) The loosening of surface materials and landslides driven by the Wenchuan earthquake resulted in an increase in sediment discharge into the river, bringing about a great disaster which will need to be addressed in the coming decades.