The concept of wave energy is fundamental to understanding coastal erosion. Wave energy is expressed here as wave energy density, which means the amount of energy (ability to do work) in the wave, over 1 square meter of sea surface. On a sandy coast, high wave energy density means much stirring of the sand, whereas low wave energy density means little stirring of the sand. Along the Atlantic coast waves are very energetic, whereas along some parts of the Gulf of Mexico there is very little wave action. The small blue arrows indicate--in general--the direction of the movement of sand. On the east coast, for example, this combination of arrows along with high wave energy density means severe beach erosion. Mangrove swamps, reefs of several types, and other coastal features affecting beach erosion are also shown.
