An existing long-term morphodynamic model for tidal inlets and basins is studied and also extended; a new boundary condition is considered: a river in the system. To understand how the model predict the behaviour of these systems and how these systems evolve, different cases are studied, as well as a sensitivity analysis is made due to the nature of some input data. For this purpose, a simplification of the equitons that lead the model is presented. Finally, the model is applied to a real case, to the Bay of Santander, where due to the harbour sited in the bay, human dredging works are needed