Wave refraction at a shoreline occurs when a wave approaches the shoreline at a straight angle, and the wave crest over the shallower part of the water moves slower than the wave crest over the deeper water. The wave refracts, or bends, because the depth beneath the crest varies. The wave crest over the deeper water eventually meets the crest over the shallower water, making it parallel to the shore.
Wave refraction also occurs around a circular island. A wave approaches from one direction and wraps around the island. The wave crest approaches the land in a parallel manner on all sides of the island.
Another concept that describes the movement of waves, diffraction, occurs when waves meet an obstacle that pierces their surface, such as an island. Other behavioral characteristics of waves include shoaling, which occurs when waves enter shallow water, and breaking, which occurs when the height of the wave becomes the same size as the local water depth.
Waves are defined by height, length and period. The height is the distance between the lowest and the highest part of the wave, known as the trough and the crest, respectively. Length is the distance between wave crests, and period is the time it takes for two successive crests to pass a fixed point.