Simulation of rainfall-induced debris flow considering material entrainment

• An efficient depth-integrated particle method for debris flow simulation is tested.
• Soil erosion and sedimentation is successfully modeled by diffusion equation.
• Loose soil deposit is distributed at the base of valley by dry slope failure simulation.
• Entrainment of loose soil deposit played a crucial role in 2010 Zhouqu debris flow.

In order to simulate soil erosion and sedimentation processes of debris flow, a depth-integrated particle method with soil-water mixing model is proposed. In the model, each numerical particle represents a mixture of soil grains and water with a certain soil volume concentration and can exchange the soil mass with the neighboring particles according to the diffusion equation. A unique relationship is also assumed between the soil volume concentration and its critical deposition angle to compute the bottom shear stress acting on the flowing numerical particles. Therefore, the model only contains three major mechanical parameters: the classical Manning coefficient, the critical slope angle for the loose soil deposit at the base of valley, and the diffusion coefficient to control the soil water mixing process. In addition, a two-step simulation method is proposed to evaluate the initial distribution of the loose soil deposit in the valley bottom. The model is initially validated by a laboratory flume experiment taken from the open literature, and adequate values of the mechanical parameters are determined. Next, the model is applied into the case study of the 2010 debris flow event in Zhouqu, and the simulation results are compared with the field investigation, as well as the post-event satellite images. The affected area, the travel distance, and the flow velocity statistics exhibit good agreement.