Deposition characteristics of debris flows in a lateral flume considering upstream entrainment

The sediment deposited by debris flows in rivers is a common cause of mountain disasters. The deposition characteristics of debris flows are strongly affected by the entrainment during the transportation process and the water depth in the river channel, but how is poorly understood. Here, the effects of the released flow volume, flow density, bed sediment and water depth on the deposition process of debris flows are investigated for a total of 22 different tests. Detailed topographic surveys of deposit lobes are conducted using a 3D laser scanner with high precision. The slopes of lobes are largely determined by the flow density and bed-sediment composition. However, the effect of released flow volume on the lobe slope is relatively limited. The lobe areas projected onto the horizontal plane display dumbbell or trapezoidal shapes depending on deposit volume, and the cross sections along the lateral flume present a Gaussian distribution for flows after bed-sediment entrainment. The lobe area is reduced and lobe height is enhanced with an increase of water depth, contributing to a steeper deposit. Partial, submersed or complete blockages occur, depending on the debris-flow volume and water depth. This study improves understanding of the deposition features and may aid future hazard assessments of debris flows.