Multi-scenario simulations for quantitative assessment of debris flow chain hazards in southwestern China

• Integrated field surveys and numerical simulations reveal debris flow dynamics. • A quantitative framework effectively assesses debris flow hazards. • Findings support local debris flow risk management and disaster prevention. Following the catastrophic Wenchuan earthquake in 2008, debris flows have repeatedly obstructed rivers across China’s southwestern mountainous regions, triggering numerous flood disasters and subsequent cascading effects. Ethnic minority villages in these areas are predominantly situated within alpine canyon zones highly susceptible to seismic activity, rendering them exceptionally vulnerable to flood disaster chains initiated by debris flows. This study focuses on Luobajie Gully in the southwest mountainous region as a case study to elucidate the chain hazard responses associated with debris flows and to highlight the critical importance of such research. Comprehensive field investigations provided essential data—including sediment depth, flow density, and velocity—for numerical simulations aimed at assessing potential hazards. Simulation results demonstrate that only debris flows triggered by a 100-year rainstorm event cause channel blockages in Luobajie Gully, leading to significant rises in river water levels due to dammed floodwaters. The resulting flooding reaches maximum water depths within the inundation zone of the accumulation fan, exerting the most substantial impact on adjacent industrial areas. A quantitative risk assessment of 100-year debris flow events was carried out to evaluate the potential hazards. This study analyzes in detail the movement process and potential hazards of the Luobajie Gully debris flow through detailed remote sensing image analysis, field investigation and numerical simulation, and emphasizes the necessity of taking effective preventive and control measures to reduce the associated risks. Since the Heishui River traverses the Wenchuan earthquake area, there are still several potential debris flow gullies, and potential debris flows may pose a non-negligible threat to the entire earthquake area. The model and theory presented in this paper can be effectively applied to the simulation and early warning of other potential debris flows in the earthquake area under similar circumstances, thus facilitating their wide application in flood risk management.