Numerical investigation of post-seismic debris flows in the epicentral area of the Wenchuan earthquake

Since the 12 May 2008 Wenchuan earthquake, numerous catastrophic debris flows have occurred in the Wenchuan earthquake-stricken zones. In particular, on 14 August 2010, long-duration, low-intensity rainfall triggered widespread debris flows at the epicenter of the Wenchuan earthquake. These flows caused serious casualties and property losses. In this study, a novel approach combining a soil-water mixing model and a depth-integrated particle method is applied to the analysis of the post-seismic debris flows in the epicentral area. The presented approach makes use of satellite images of the debris flow in the affected area. It is assumed that debris source materials are primarily generated from slope failure during the earthquake. Debris flows are initiated after different amounts of cumulative rainfall according to diffusion governing equations. The debris flow disaster is investigated in terms of volume, concentration, discharge, velocity, deposition thickness and affected area by setting the cumulative rainfall, Manning coefficient and diffusion coefficient to 38 mm, 0.1 and 0.004 m² s⁻¹, respectively. Although the thickness and volume of debris source materials are underestimated in this study, the numerical results, including the volume concentration, velocity, discharge and the affected area are in good agreement with the actual observations/measurements of the debris flow events. Adopting a simple and efficient numerical model, systematic analysis of the entire debris flow generation process not only contributes to understanding the mechanism of initiation, transportation and deposition, but is also very useful in designing effective protection structures according to the distribution characteristics of the main parameters. Additionally, the coupling effect of multiple debris flows is discussed.