Crescentic bars emerge as free instabilities of the coupling between topography and water motion. Their long term behaviour will be studied in the real case of the French Aquitaine beaches by using the 2DH numerical model MORFO55. For the first time, the equilibrium state of a crescentic bar system is obtained, in the case of steady incident wave conditions. Due to non linear interactions, the final wave length of the system does not inevitably increase with the incident wave height. Finally, the study of variable incident wave conditions suggests that the equilibrium state may depend on the initial conditions.