Debris-flow occurrence probability on hillslopes

This paper derives a critical relation for the occurrence of a debris flow, based on the condition that the driving stress exceeds the resistance stress acting on the inclined soil layer of a hillslope. The uncertainty of significant hydrogeological variables in the critical relation is analyzed and evaluated. Considering the uncertainty of such hydrogeological variables, we derive an equation for debris-flow occurrence probability, based on the first-order, second-moment method (FOSM). This equation is used to estimate the occurrence probability of debris flows on a hillslope in Tunshing village, Taiwan. The result is compared with that by the Monte Carlo simulation method (MCSM).