The Carnot dam is a structure of more than 3 km in length that protects the harbour, the port of Boulogne-sur-Mer and the urbanised areas of the dominant houles of the western and south-west sectors. This structure helps to limit the increase in port agitation and the height of swell affecting the port area and the coast. In addition to its role in the safety of navigation, the dam is essential to limiting the risk of flooding by crossing and erosion. It protects the coastline along Boulevard Sainte-Beuve, urban areas, homes, shops, activities and facilities, the Nausicaa Sea Centre and all the port areas gained on the sea after its construction. The dike is violently hit by the Channel Houles. Despite regular monitoring and maintenance, it now presents problems requiring work to restore a sufficient level of reliability and to ensure its role in protecting populations, activities and equipment. The proposed works will rehabilitate the structure, strengthen its protective role and ensure its sustainability by maintaining the current structure and configuration; they consist of an upgrade of the Digue whose current state no longer ensures its function.