The Effect of Entrainment Model on Debris-Flow Simulation—Comparison of Two Simple 1D Models

Debris flows, consisting of water–sediment mixtures that travel rapidly along channels, often carry materials ranging from fine sediments, such as clay or silt, to large boulders, resulting in significant impacts on lives and infrastructure. Accurate estimation of the debris-flow behavior is crucial for establishing effective debris-flow mitigation strategies. However, the dynamic entrainment process complicates simulations because it significantly affects flow characteristics, including velocity, depth, and sediment concentration. In this study, we analyzed the effects of entrainment on debris flow simulations using two one-dimensional models for a debris-flow event that occurred in 2011 in Seoul, Republic of Korea. The results show that including entrainment improves the accuracy of the debris-flow simulation. Moreover, a scheme dealing with entrained sediment in the governing equations is important for reproducing debris-flow characteristics. These findings highlight the necessity of entrainment models for effective debris-flow simulation, with implications for enhancing debris-flow hazard mitigation strategies.