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The term beach describes the temporary covering of rock debris (sand, gravel, pebbles, and rock fragments) which accumulates on the wave-cut terrace. Beaches may extend for hundreds of miles or may be patchy, depending on the development of the wave-cut terrace and the supply of sand, gravel, and pebbles. Although some beach material comes from wave erosion, the largest amount is often supplied from the land (stream erosion, slope erosion). Storm waves usually cause the removal of material whereas the normal waves usually cause the deposition of the clastic material through lateral accretion.
As the waves come near the shore, the shallower depth begins to interfere with the orbital motion of the waves, and when the orbital velocity exceeds the wave speed, the crest begins to curl and eventually break. This energy causes the water to be thrown forward against the shoreline.
Because waves usually approach the shore at an angle, the beach material tends to be moved in a preferred direction (longshore drift). As the wave breaks, the swash (forward motion) carries the material up the beach at an angle; as the velocity of the backswash drops, the material settles farther down the beach. The path of transport is somewhat parabolic as the sand, gravel, and pebbles migrate parallel to the shore.
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