Give an idea how sea defences could help to protect coastlines?

Briefly outline a few different sea defences, including, but not limited to, sea walls, groynes and boulder barriers. They can protect the base of cliffs from erosion as well as prevent coastal flooding. Groynes can prevent the movement of sediment along the shore via longshore drift, thus facilitating the build up of beaches. Some sea defences can absorb the wave energy, thus reducing erosion. Also mention soft engineering techniques suchas managed retreat and beach nourishment.