Modeling the Atami debris flow using the depth-integrated particle method and GIS: Flow characteristics and future risk assessment

The Depth-Integrated Particle Method (DIPM) is a numerical approach for simulating sediment disasters, such as debris flows and mudflows. This study applies DIPM to the 2021 Atami debris flow in Shizuoka Prefecture, Japan, triggered by heavy rainfall and slope collapse. DIPM models the moving mass as computational particles, represented as soil columns, with pairwise interactions between particles derived from the hydraulic gradient of the soil columns. A numerical test confirmed the reliability of the hydraulic pressure gradient model. Digital Elevation Models (DEMs) were created from pre-disaster grid data at 0.5-m resolution, processed into 5-m and 1-m meshes. Sensitivity analyses identified optimal parameters (Manning's coefficient, $n$ ​= ​0.1; critical deposition angle, $i_{cr}$ ​= ​8.5°), closely matching observed flow velocities and average sediment deposition height (1.65 ​m). Cross-sectional comparisons at the existing check dam validated the model, demonstrating its applicability for hazard assessment. DIPM also evaluated the Izusan check dam, confirming its capacity of 10,800 ​m³ aligns with simulation predictions, supporting its role in debris flow mitigation. These findings highlight versatility of DIPM for debris flow modeling and risk evaluation.