Destructive Waves: found on steep beaches, are steeply breaking and mainly responsible for coastal erosion. Their backwash is much stronger than their swash.

Destructive process

In storm conditions particularly, the process can cause significant erosion to beaches (an example being Barton on Sea on the English coast) and therefore is a threat to coastal communities that rely on their beaches for protection from more serious erosion. The need is most obvious where there are permanent structures on the shore. The loss of first the beach, then of old, glacially deposited, sediment to longshore drift resulted in the loss of the English town of Dunwich in Suffolk to the sea. The problem causes coastal towns in erosional longshore drift areas to employ coastal defences such as groynes, which interrupt the downstream movement of sediment. Jetties and groynes generally do not stop longshore drift, but interfere with it to the extent of retaining some of the beach material which might otherwise be removed. When a groyne is constructed, once equilibrium has been regained, the longshore drift resumes but, if the groyne has been well-sited, some of the beach material is retained on its upstream side. This is useful in dissipating the energy in incoming waves as the retained beach breaks some of the force. The part of the shore in the “shadow” of the groyne, downstream from it, is sheltered by having the waves broken by the structure.