A small-scale physical model was build and used to study deposition processes in a planned debris basin in the French Alps. Numerical simulations were then undertaken with a 2D depth-averaged hydraulic and morphologic numerical model in order to check its ca-pability to reproduce flow and bed changes in this steep and laterally unconfined case with coarse sediment. The paper focuses on the set-up of the numerical model, which en-ables to get results very similar to the physical model. Old and state-of-the-art formula-tions for friction law and for bedload transport equation were compared. More precisely, the best performance were obtained with a friction law valid for small relative flow depth and bedload transport formulation using a non-threshold equation.