Numerical Simulation of a Rainfall-Induced Debris Flow: A Case Study in Tianquan County, Southwest China

Debris flows are widely distributed in the mountainous areas such as Southwest China, which are liable to break out following rainstorm and seriously threatens the safety of local villagers and public transportation facilities. Thus, it is extremely significant to study the formation mechanism of the rainfall-induced debris flow. This paper took the Xiaogoucun debris flow as an instance, and analyzed its formation mechanism based on field investigation and remote sensing. It was found that the main controlling factor of the Xiaogoucun debris flow was that accumulated rainfall exceeds the threshold of the study area. A large scale of previous loose deposits in the gully and the favourable topographic conditions dramatically contributed to the volume of flow-out materials and hazard risk of the debris flow. On the basis of the improved Voellmy-Salm fluid model, the three-dimensional dynamic simulation software RAMMS was utilized to simulate the evolutionary process of the Xiaogoucun debris flow. The calibrated Coulomb friction coefficient (μ) and viscous turbulent friction coefficient (ξ) in the catchment were respectively determined as 0.200 and 220 m/s2. The simulation results unraveled the mechanism of rainfall-induced debris flow from the aspects of the flow height, velocity, and depositional area. The simulation results were in good accordance with the field investigations. This study applied an efficient approach to the assessment of rainfall-induced debris flow, and the research productions can provide guidance for the design of debris flow protection engineering in mountainous areas of Southwest China.