Numerical simulation on post-earthquake debris flows: A case study of the Chutou gully in Wenchuan, China

Abstract

Since the 2008 Wenchuan earthquake, post-earthquake debris flows have severely threatened people’s lives and the safety of public transit facilities, making particularly crucial to understand their formation mechanism. We focused on the Chutou gully debris flow and analyzed its formation mechanism based on field investigations and satellite images. The main inducing factor of this debris flow was a continuous heavy rainfall that exceeded the threshold of the study area: this, combined with the large amount of loose material created by the earthquake, dramatically promoted the volume and hazard degree of the debris flow. The three-dimensional debris flow simulation software RAMMS, based on an improved Voellmy–Salm fluid model, was used to simulate the movement process of the Chutou gully debris flow. The calibrated Coulomb friction (μ) and viscous turbulent friction (ξ) coefficients in the study area were 0.225 and 180 m/s2, respectively. The simulation results revealed the post-earthquake debris flow mechanism in terms of flow height, velocity, flow rate, and deposition area. The results of the numerical simulation were in good agreement with those of the field investigations. In particular, it was found that the peak flow of debris flow upstream of the Chutou gully was shorter in duration than the one upstream; however, due to the convergence of the branch gully, the downstream peak flow of debris flow increased significantly, while a large amount of solid material stranded downstream of the channel. Notably, this process is prone to occur again. This study proposes a new post-earthquake debris flow evaluation method, and its results are of reference value for the design of debris flow prevention engineering in meizoseismal areas.