Effects of material composition on deposition characteristics of runoff-generated debris flows

The loose material in the mountain gullies is prone to form serious debris flow disasters under appropriate hydrodynamic conditions. The various compositions of these loose materials often lead to very large differences in the runout distances and the inundated areas. However, the mechanisms of the influence of material composition on the deposition characteristics of debris flow remain unclear, and studies are lacking on the influence of material composition on the deposition characteristics of runoff-generated debris flows. This study conducted experiments using different water discharges, flume slopes, and grain size distributions. The deposition processes of debris flows were observed, and their deposition patterns were explored. The effects of material composition on flow regimes, runout distances, inundated areas, and deposit geometries are revealed. The results showed that there are three types of debris flow, and their deposition patterns are different. The relationships of the Bagnold number and Friction number concerning the volume solid concentration were exponential. The mean mobility angle, a function of the upstream terrain slope, was established to assess the runout distance of debris flows with different flow regimes. Additionally, a criterion for identifying debris flow types was established by combining dimensionless runout distance and dimensionless slope. This study not only improved the observation of experimental phenomena in the deposition process of runoff-generated debris flows but also deepened the understanding of the mechanism of the influence of material composition on the deposition characteristics.