Dynamic process of a typical slope debris flow: a case study of the wujia gully, Zengda, Sichuan Province, China

On July 25, 2020, a debris flow occurred in the Wujia Gully, Sichuan Province, China. The last debris flow in this gully occurred 70 years ago and severely impacted the area downstream. The primary goal of this study was to analyze the impact of the topography on the movement process of the debris flow. To gain a precise understanding, a dataset was compiled, including metrological data, field data, accounts from locals, field sampling to obtain specific information using Unmanned Aerial Vehicle (UAV) photography, and the rheological properties of the debris flow slurry obtained through soil mechanics and rheological experiments. The movement process of the debris flow was simulated using the depth-integrated continuum approach. Based on numerical simulation analysis, the influence of the Wujia gully’s topography on the debris flow’s dynamic process was examined. It was found that the debris flow in the Wujia Gully was a typical viscous debris flow, and the debris flow slurry had the properties of a Bingham fluid. The dynamic process of the debris flow was divided into four stages: an acceleration stage, a deceleration stage in the channel, a smooth movement stage, and a slow accumulation stage. The topography was the main factor controlling the formation of the four stages of the dynamic process. Furthermore, Manning's resistance coefficient did not change the debris flow’s dynamic process, but it significantly affected the velocity and duration of each stage. The results of this study provide a reference for future research on debris flow kinematics and flow channels of typical slope debris flows and their movement processes.