Debris flow is a highly destructive natural hazard that threatens lives, infrastructure, and the environment in mountainous regions. Sabo dams are commonly employed as mitigation structures to reduce flow energy and control sediment transport; however, detailed information on velocity distributions around these structures remains limited. This study experimentally investigated the velocity characteristics of debris flow around a Sabo dam using Particle Image Velocimetry (PIV). Laboratory flume experiments were conducted using a 1:70 scaled model under twelve test conditions combining three flume inclination angles (10°, 20°, and 30°) and four Sabo dam upstream face inclination angles (0°, 15°, 20°, and 25°). A high-speed camera operating at 400 frames per second captured 2,000 images for each case, and velocity fields were analysed using PIVLab software. The results revealed that debris-flow velocities increased with increasing flume inclination, while the upstream face inclination of the Sabo dam exerted only a minor influence on the overall flow velocity. Area-averaged velocities ranged from 1.51 m/s at a flume inclination of 10° to 2.00 m/s at 30°. Individual particle velocities varied between -8.6 × 10⁻³ m/s and 3.3 m/s, with negative velocities indicating temporary backflow caused by flow obstruction at the dam face. The highest velocities were generally observed during the 2^nd second of flow, after which velocities gradually decreased due to the reduction in upstream water head in accordance with Torricelli’s principle. PIV analysis successfully captured detailed spatial and temporal flow behaviour, including turbulence generation, hydraulic jumps, and recirculation zones around the dam. The findings demonstrate the effectiveness of PIV as a tool for characterising debris-flow dynamics and provide valuable data for improving Sabo dam design and validating numerical models for debris-flow hazard mitigation.

particle image velocimetry,sabo dam,effectiveness,debris flow dynamic