Hard engineering techniques involve building rock or concrete structures, most commonly sea walls, jetties, rock islands, rock aprons and breakwaters. Piles of large rocks are especially efficient at dissipating wave energy as they are able to move, and water can percolate through them.
Soft engineering most commonly involves encouraging the build-up of land between the sea and the object being protected, most commonly a beach, but sometimes a salt marsh or dune system. Beach nourishment takes place at many coastal towns in western countries. Many places encourage sediment accumulation by constructing groynes, out of rock or concrete. These cause sand carried by longshore drift and sea currents to be deposited.
The alternative to coastal defenses is managed retreat.