Abstract : In 1998, Naaim and Gurer proposed the "two-layers" model for snow avalanches. The avalanche is described as a superposition of two layers. Near the ground is a basal layer in which the flow is collisional. This layer is overlaid by an upper layer - a turblent two-phase flow. Each layer has its own dynamics. Mass and momentum transfers take place in the interface zone separating the two layers. This study presents an analysis of this interface, viewed as the bottom of the two-phase flow of the upper layer. A modeling with saline density cloud flowing in an immerged canal has been carried out. Measurements have been performed using image processing. Influence of the flow bed structure on the flow dynamics and erosion locates have also been studied. These results have been compared with the bibliographic data and a conceptual analysis of the erosion phenomenon. An analytical formulation of erosion has been proposed. It consider an attenuation of turbulence due to the presence of suspended particles in the flow. This has been integrated in a numerical modeling, putting in evidence the link with experimental results.