Finally, in this section we discuss the hydrodynamic description of the Inclined Plane Model. We use the equations proposed by Brey et al. [39,91], with the values of the transport coefficients that they have calculated. The problem can be solved but a close solution needs good boundary conditions. This is a non-trivial task, because the external parameters (e.g. the amplitude and frequency of the vibrating bottom, as well as the longitudinal size of the system) are connected to the bulk profiles through non-hydrodynamic layers (bottom and top).