Variable-concentration and boundary effects on debris flow discharge

The uniform flow of natural debris mixture is generally modeled assuming a uniform solid concentration and the absence of lateral walls. The resulting flow discharges are however higher than those observed and, in case of erodible boundaries, the equilibrium between the moving and non-moving mixtures cannot be simulated. Also, this model can't simulate the effect of lateral rigid boundaries that generate velocity and lateral concentration gradients. This paper describes a numerical model to determine the concentration and velocity distribution in the two directions transverse to the flow. The model is applied to a uniform laminar flow of a mixture with a shear-thickening Herschel-Bulkley constitutive behavior, with rheological parameters expressed in terms of the local solid concentration, and allows the simulation of different condi-tions in the presence of both erodible and rigid boundaries.