Hongchun Catchment (Southwest, China) Debrisflow Analysis and Reconstruction: Geomorphological and Coupled Modeling Approaches

Abstract

The Wenchuan earthquake of May, 2008 led to an abundance of loose landslide debris being present on the slopes and in the gullies of Hongchun catchment, South West, China. The debris later served as source material for the July 21st, 2011 rainfall-induced debris flows in the Hongchun catchment. The main objectives of this research are: to understand the catchment hydrological processes, to inventorize and characterize the landslides bodies as potential sources of debris flow and to reconstruct the debris flow events. Geomorphological mapping of the landslides revealed 38 of them. However, these landslides were characterized according to scarp and body. The geomorphological mapping was supported by field observations and historical knowledge gathered through interviews revealed that the co-seismic landslides were the potential source of debris flows in the catchment. Putting the hydrological processes into perspective, the Limburg soil erosion model (LISEM) shows hydrograph with three peaks corresponding to discharge from rainfall water but produce little runoff. Thus, antecedent rainfall may have saturated the debris/soil on the slope that triggered the debris flow. The LISEM hydrograph from LISEM and Flo-2D models were coupled and reconstructed the debris flow. The debris flow results shows a maximum flow velocity of 2.9m/s, area extent of 975000 km2, average flow depth of 11.2 m and impact force of 4,559 N/m2. Finally, the debris flow volume of 171,350 m3 representing 80.7% of the total debris flow volume was reconstructed.