Simulation prediction and risk evaluation of debris flow in gullyprone ditches of Lajing Village, Lanping County, Yunnan Province, China

Lanping County, located in the northwestern part of Yunnan Province, is characterized by unfavorable geological conditions. In recent years, debris flow disasters have frequently occurred in this area due to the influence of rainfall, yet there is a lack of accurate disaster risk evaluations. To enhance early warning preparedness for debris flow disasters in the region, the FLO-2D model was employed to perform an inverse analysis of a historical debris flow event in Lajing Village, Lanping County. Based on the parameters obtained from this analysis, predictions of the dynamic characteristics and risk assessments were conducted for another debris flow-prone gully under three rainfall recurrence period conditions: 20, 50 and 100 years. The results indicate that in Gully No. 2 of Lajing Village, the siltation depth and maximum flow velocity of debris flow increase with the intensification of rainfall. Under extreme rainfall conditions, the siltation depth at the trench bottom is expected to exceed 2.5 m, and the maximum flow velocity in the transportation zone may exceed 5 m/s, leading to the accumulation of more loose materials in the deposition area and creating significant safety hazards. The high-risk zones in gully No. 2 are primarily located in areas with high flow velocity and mud depth, around densely populated residential areas near the gully, and within the debris flow accumulation zone. The findings of this study provide valuable references for disaster prevention and mitigation engineering, as well as for early warning systems in the region.