Effect of debris-flow sediment grain-size distribution on fan morphology

Abstract. Knowledge of how debris flows result in the fan-shaped morphology around a channel outlet is crucial for mitigation debris-flow-related disasters and investigation previous sediment transport from upper channel. Therefore, using flume connected to deposition area (inundation plane), this study conducted fan-morphology experiments assess effects differences grain-size distribution within on changes fan morphology. Two types debris-flow material, i.e., monogranular particles comprising monodispersed multigranular polydispersed particles, were used generate experimental flows, respectively. By adjusting average grain size coincident between we generated two flow with similar mixture hydrographs but different distributions flume. Although depths mostly before start runout at area, distances front shorter than those flows. The difference distance was responsible variations extent location which changed their direction descent, resulting shapes morphologies fans response distribution. descent repeatedly, morphological symmetry increased time during formation irrespective In contrast similarity rate change symmetry, shift directions eventually asymmetry expanded scale deviations test runs. wide-ranging likely complex high degree asymmetry.