Theoretical, experimental, and numerical studies of flow field characteristics and incipient scouring erosion for slope with rigid vegetations

Under the action of continuous rainfall, the coupling linkage between runoff and seepage can cause erosion of non-cohesive soil particles on vegetated slopes. A nonlinear turbulent-seepage coupling model is established to study the flow field characteristics and incipient scouring erosion of the vegetated slope. The fluid in the turbulent region is governed by the Reynolds averaged Navier-Stokes. Biot's poroelasticity theory describes the flow in the vegetation region. The seepage in the soil region obeyed the Darcy-Brinkman equation. Analytical solutions of the vertical velocity profile and safety factor (sliding and rolling) of the particle incipient motion are derived based on the coupling between turbulence and seepage. The velocity expression is found to be in good agreement with the existing experimental data of both emerged and submerged vegetation conditions, respectively. The velocity distribution above the surface follows a logarithmic pattern, while below the surface, non-linear seepage occurs with a transition layer that deviates from Darcy seepage. In addition, the particle incipient motion is verified by the physical flume souring test under none, sparse, and dense vegetation, respectively. The absolute error between the theoretical calculation and the physical test is within 5%. Furthermore, the critical water depth is nonlinearly negatively correlated with the energy slope. Finally, a CFD-DEM coupling numerical model is employed to further observe the scouring erosion of the sparse and dense vegetated slopes with the same conditions as the physical test. The numerical results show that the scouring erosion exhibits discontinuous behavior and the soil particles between the two vegetation are more vulnerable to scouring than those in other locations. After scouring, the inertial porosity of the vegetated soil slope decreases while the porosity in the surface area increases.