What is meant by Constructive wave? How it is different from Destructive wave?

Constructive Wave is a series of gentle waves rolling in steadily on to a coast at about 6-8 a minute. They are created in calm weather and are less powerful than destructive waves. They have a long wavelength, and are low in height. It has a powerful push of the Swash, and a less powerful Backwash due to frictional retardation. It thus tends to move material up a beach, so building up ridges.

When a wave breaks, water is washed up the beach – this is called the swash. Then the water runs back down the beach – this is called the backwash.With a constructive wave, the swash is stronger than the backwash. With a destructive wave, the backwash is stronger than the swash.