With a constructive wave, the swash is stronger than the backwash. With a destructive wave, the backwash is stronger than the swash. The backwash then flows back to the sea in a straight line at 90°.

Destructive waves have more energy and often cause coastal erosion. Destructive waves are steep and arrive at the coast rapidly (between 12-15 per minute). Their strong backwash will pull beach ...