Wave shoaling and refraction

The processes of wave shoaling and refraction change the height and direction of waves as they interact with reefs of various shapes and sizes. Significant refraction can occur along the reef edge/rim of an elongated reef aligned with the direction of the approaching ocean waves, As waves break on the reef rim, alongshore currents will transport sediments toward the leeward end of the reef. Diffraction behind the reef will make the sheltered zone behind the reef less sheltered than might be expected. Interference of refracted waves on the reef platform may result in the formation of a windward shingle bank or cay, while sand cays form in the focal zone created by the refracted waves toward the leeward end of the reef. The shape and location of these interference and focal zones vary with changes in wave direction and wave period with consequent modification of the shoreline alignment of cays as their beaches respond to changes in alongshore transport around them.