The aim of this study was to develop a numerical model for simulating the surface erosion occurring at a fluid/soil interface undergoing a flow process. The balance equations with jump relations are used. A penalization procedure is used to compute Stokes equations around obstacles, with a fictitious domain method, in order to avoid body-fitted unstructured meshes and to use fast and efficient finite volumes approximations on Cartesian meshes. The water/soil interface evolution is described with a Level Set function. The ability of the model to predict the interfacial erosion of soils is confirmed by presenting several 2-D simulations.