Analysis of the Erosion-Sedimentation Characteristics and Dynamic Evolution Process of Mountain Flood Debris Flows in Xiaogou, Hanyuan, Sichuan.

Objectives: The mountain flood debris flow disaster triggered by the heavy rainfall event on July 20th in Hanyuan County, Ya'an City, Sichuan Province, is a typical example of a rainstorm-induced mountain flood debris flow disaster. Due to the complex topography, concentrated and intense rainfall, the region is highly susceptible to such disasters, which have caused significant impacts on the local ecological environment and the livelihoods of its residents. Methods: This research investigates the Xiaogou mountain flood debris flow using Small Baseline Subset InSAR (SBASInSAR) technology and the OpenLISEM model. Incorporating Unmanned Aerial Vehicle (UAV) imagery and groundbased observations, it analyzes the erosion-sedimentation patterns and dynamic progression of debris flow within the Xiaogou watershed. Results: The erosion rate in the Xiaogou watershed is 2588 m³/(km²·year), with an annual erosion volume of 1.63×10⁴ m³/year. Under rainfall frequencies of P=5%, P=2%, and P=1%, the maximum flow velocities of the mountain flood debris flow in Xiaogou are 18 m/s, 17.78 m/s, and 17.64 m/s, respectively, while the maximum sediment depths are 6.38 m, 6.69 m, and 6.89 m. At rainfall frequencies of P=2% and P=1%, a significant amount of solid material is discharged, causing substantial impacts on the structures at the mouth of the gully. Some of this material is flushed out and participates in the river evolution, potentially raising the riverbed and causing a partial blockage of the Baiyan River, which presents a significant threat to the downstream industrial park. Conclusions: The results of this study help improve mountain flood debris flow early warning capability in the southwestern mountainous regions and offer a sound scientific foundation for post-disaster emergency response and disaster prevention strategies.