Factors affecting the behavior of debris flow run-out include source material composition, volume of initial failure, slope angle at source, source slope morphology, degree of saturation of initial failure material, the type, depth and degree of saturation of path material, presence of surface water in slide path, vegetation along run-out path, and path confinement. The effective soil porosity is expected to have a great effect on some of these factors. Although many studies using a numerical simulation have been performed to analyze debris flow run-out, the effect of ESP (Effective Soil Porosity) has not been considered as a main contributor to the length of debris flow run-out. Therefore, this study examines the effect of ESP variation on travel distance of debris flow run-out. The results demonstrate that ESP is a dominant factor in determining the travel distance and the distribution of debris flow; that is, when the slope had a larger ESP value, the slope had greater water content in the sliding segment, resulting in a faster and longer travel distance, as well as in a broader distribution of debris flow. Consequently, a larger ESP value may increase the risk of damage in the downstream region
