Risk assessment of debris flow disaster in Zhalong gully, Minxian County, Gansu Province based on the FLO-2D model

Debris flows pose a serious threaten to human safety and ecological stability due to their sudden onset and destructive power. Zhalong gully in Min County, Gansu Province, are frequent, is prone to frequent debris flow events, highlighting the need for disaster prevention and early warning. Based on the FLO-2D numerical simulation model, rainfall intensity data with return periods of 10 years, 20 years, and 50 years were selected. Combined with a high-precision digital elevation model (DEM) and debris flow parameters determined by field investigation, the movement process of debris flow (flow velocity, accumulation depth, and range) under different rainfall return periods was simulated, and disaster risk zoning was conducted. Buildings, roads, and land within the affected area were selected for vulnerability assessment, and a risk zoning map was generated by combining the results with a risk assessment model. With the increase of rainfall frequency, the peak flow, flow velocity, and accumulation depth of debris flow increased significantly, and the hazard was the highest under the 50-year return period rainfall. High-risk areas were concentrated in downstream accumulation zones, and the increase in rainfall frequency raised the risk for buildings in low-risk areas. The results of this study are of great significance for debris flow disaster prevention, early warning, and risk management, and provide a foundation for subsequent research on precise and quantitative risk assessment methods. This study combines numerical simulation of debris flow with vulnerability assessment of buildings considering impact pressure, and applies principal component analysis to evaluate the vulnerability of roads and land, thereby constructing a multi-dimensional and high-precision comprehensive risk assessment framework.