Simulation-Based Sensitivity Analysis of Check-Dam Height Effects on Downstream Debris-Flow Depth for Structural Countermeasure Scenarios

Jun Katagiri , Hidetaka Saomoto, Takayuki Shinohara, Sho Kimura

Check dams can influence debris-flow propagation, but their effects may depend on location, height, and local topographic conditions. This study evaluates the sensitivity of downstream debris-flow depth to check-dam height scenarios using numerical simulations of a mountainous catchment in Atami, Japan. Six hypothetical check-dam locations were placed along the torrent, and 4,877 valid cases were generated by varying their heights. The maximum debris-flow depth at a downstream evaluation section was used as the response variable. A machine-learning surrogate model was used to summarize the simulation-derived relationship between dam-height combinations and downstream flow depth, and location-dependent sensitivity was evaluated using permutation importance. The highest sensitivity was found at a midstream check-dam location, while an adjacent downstream location also contributed substantially. Longitudinal topographic analysis suggests that this pattern may be related to local terrain modification and erosion–deposition tendencies between adjacent dam locations. These results indicate that check-dam height effects cannot be interpreted solely from downstream distance. The study provides a reproducible scenario-screening workflow for preliminary interpretation of debris-flow mitigation scenarios, distinct from event reproduction, design optimization, or design-criteria development.