Debris flow enlargement from entrainment: A case study for comparison of three entrainment models

Abstract Material entrainment can significantly magnify debris flow volume and increase its destructive power. Despite great research efforts, entrainment is still not well understood. To meet the needs for debris flow simulation and hazard analysis, it is of practical significance to understand and evaluate existing entrainment models. In this study, we evaluate three entrainment models on an integrated single-phase continuum debris flow simulation platform. The well-documented Tsing Shan debris flow in 1990 in Hong Kong, with an initial landslide volume of 2500 m3 and a final deposit volume of 20,400 m3, is used as a benchmark to compare the three models. The characteristics and performance of each model and its model parameters are discussed. Although numerical results achieve reasonable agreement with detailed field investigations, some parameters are still determined empirically and subjectively. Despite of the imperfection, these models can be used for debris flow hazard analysis in the Hong Kong region with similar conditions. More physically-based entrainment models considering two-phase flow need to be adopted and further developed in the future.