Refraction/diffraction at coastal structures - Essay Example

This effect is due to the changes in wave height along the crest of the same wave (“Shoaling..”). Water waves that have undergone diffraction and have bent into the lee side of the island can interfere there and produce steep hazardous seas. Wave refraction is the process in which water waves bend as they reach shallow water near the shore, due to a change in wave velocity. The wave velocity decreases when the wave base hits the ocean bottom. Since the wave in general is approaching the shore from an angle, the wave base on one side of the wave touches the bottom before the other side.

This causes the wave to bend. The part of the wave crest farther out to sea in deeper water moves faster than the part of the wave crest closer to shore that has reached shallow water. The deep water part of the wave catches up to the rest of the wave and the whole wave becomes parallel to the shore. One consequence of wave refraction is the straightening of beaches. Parts of the coast will erode more slowly and project out into the ocean. Refraction will concentrate wave energy on these points, and sand will build up faster at eroded areas between projecting points.

Wave refraction can affect a wave approaching a circular island so that the waves will bend around the island and waves will hit parallel to shore all the way around the island (“Shoaling..”). However, if the island is atleast a few wavelengths wide, there will be a shadow zone of the lee side of the island (see fig. 1, point A). Further out to see from this point will be an area (fig. 1, point B) where water waves coming from opposite directions will interfere and weaken. Still further out will be an area (fig.

1, point C) where the waves from opposite directions constructively interfere and focus the wave energy, resulting in dangerous seas. Wave refraction can also occur at underwater sea banks, which can act as a water wave lens, refracting and focusing the