Abstract:After the “9·5” Luding earthquake in 2022, a series of coseismic landslides and collapses occurred in the earthquake area, leading to the extensive accumulation and formation of loose solid debris. Under the action of heavy rainfall, the possibility of debris flow outbreak in the mountainous areas after the earthquake was greatly improved. On September 20, 2022, a once-in-a-decade heavy rainfall occurred in Nichang Gully, Caoke Township, Shimian County, resulting in a debris flow outbreak. During this event, massive amounts of debris flow rushed out of the gully and accumulated in the river, causing the river to be blocked. On August 14, 2023, another debris flow broke out in Nichang Gully again, leading to the silting-up of a new check dam downstream. In this study, FLO-2D was used to analyze the dynamic evolution processes of the Nichang Gully debris flow with and without a dam when the rainfall frequency reached 10%. Furthermore, the model accuracy was verified using the method of evaluation coefficient Ω . The results indicate that the modulus evaluation coefficient Ω of the dynamic evolution of Nichang Gully debris flow using this simulation method is 1.59, indicating the model's reliability. Meanwhile, the prediction of debris flow under three rainfall frequencies of 5%, 2%, and 1% was carried out. The simulation results of debris flow with prevention and control engineering under a rainfall frequency of 10% were coupled with the actual movement results of the “8·14” debris flow in Nichang Gully. The results indicate a preliminary judgment wherein the outbreak frequency of the “8·14” debris flow is once every 10 years. At the same time, the simulation results of debris flows under rainfall frequencies of 2% and 1% indicate that both lead to the failure of the control effect of the check dam. As the debris flow materials rush out of the gully, this incident causes the blockage of the river. With the change in rainfall frequency from 5% to 1%, the scope of debris flow threat also increases gradually. Overall, the threat of debris flow in Nichang Gully can be effectively reduced by adding retaining measures for the debris flow, building and maintaining the drainage channel project, and inspecting and dredging the check dam before the start of the rainy season each year.
