Identification of hidden dangers and risk assessment of slope debris flow—A case study of the Taibai Creek small watershed in Wanzhou District, Chongqing

Changtan Town in Chongqing Wanzhou District and Puzi Town in Chongqing Pengshui County experienced extreme heavy rain on July 4, 2023 and July 12, 2024 respectively. Slope-type debris flows triggered by the heavy rainfall resulted in great casualties and economic loss. Slope-type debris flows exhibit significant geomorphological differences compared to gullytype debris flows. However, existing debris flow investigation and evaluation methods are primarily designed for gully-type debris flows, there is an urgent need to establish a specialized investigation and evaluation methodology designed for slope-type debris flows. This study analyzes the coupling relationship among three key factors in the formation mechanism of slope debris flows: runoff threshold, loose material supply intensity, and slope gradient. It proposes an integrated investigation technique incorporating multi-source data and constructs a step-by-step screening process from indoor hazard identification to on-site verification. By introducing 15 quantitative indicators such as bedrock weathering degree and main channel longitudinal gradient, a refined evaluation system suitable for slope-type debris flows is established. The method was validated using the Taibaixi small watershed in Chongqing Wanzhou county, where a disaster occurred on July 4, 2023. The study successfully identified 13 potential slope debris flow hazard points that had actually triggered disasters, demonstrating the reliability and applicability of this approach under complex geological conditions.