What are constructive and destructive waves?

Constructive waves are flat and low in height and have a long wave length. Their strong swash carries material up the beach, forming a berm. They have a low frequency of between 6 and 8 waves per minute. The wave energy dissipates over a wide area which results in a weak backwash.Destructive waves have a large wave height and short wave length. They have tall breakers that have a high downward force and a strong backwash. Their frequency is high with between 13 and 15 waves per minute. Their strong downward energy helps erode beach material and cliffs. The strong backwash results in narrow beach profiles.