A beach is the zone above the water line at the shore of a body of water, marked by an accumulation of sand, stone, or gravel that has been deposited by waves and tides. This ongoing movement of sand is called longshore drift or longshore transport, and is influenced by ocean currents, wind direction, tidal movements, and oblique wave action on the shore.
Most beaches are made of sand, shells, and other materials that have been eroded by the ocean’s waves and wind. The sand, which is usually made of quartz and feldspars, may also be composed of small rocks and other debris such as seaweed.
Beach profiles change seasonally, due to a change in the wave energy experienced by different regions of the world. In temperate areas where summer is characterised by calmer seas and longer periods between breaking wave crests, the beach profile tends to be higher than in winter. This is because the gentle wave action during the summer transports sediment up the beach towards the berm where it is deposited and remains while the water recedes.
The sands and other sediments deposited by ocean waves are carried inland by onshore winds, creating dunes that often extend as far as the horizon. These are formed from a combination of wind-induced waves, longshore drift, and the accumulation of fine sediments in the turbid water column.
In the tropics, a beach’s surface may be characterized by vegetation (shrubs or palm trees), which is tolerant of seawater and saltiness and adapted to withstand abrasion from waves and sand particles. The intertidal zone, however, can be relatively barren and desert-like, or rich in palm or mangrove trees and other species able to thrive in a tropical environment.
Sands in the tropics are generally composed of a mixture of quartz, feldspars, and a smaller proportion of heavy minerals such as calcite or oolites. The softer sands and other particles that are more prone to erosion are transported inland by onshore winds, creating a variety of coastal formations such as mud flats, mangrove forests, and other sand-dominated environments.
Beach nourishment is the importing of sediments from rivers or sand quarries in an effort to restore beaches that have been damaged by erosion. The sediments, which may be substantially different in size and appearance from the natural beach sand, are deposited at the site of erosion to restore the original beach.
Depending on the nature and quantity of sediments upstream, a sand beach can vary in composition from sandy to rocky or sandstone. Sediment transported inland by onshore winds can cause the beach to sanden or sandbrick, which increases the erosive power of the moving fluid. The particle size, state of compaction, and the speed of flow and turbidity of the fluids affected by the wind and water determine the nature and composition of the deposited sand.
Generally, the lower part of a sand beach is known as the swash. In some parts of the beach, especially in the swash, smaller particles of sand are deposited, and a beach may be divided into four zones. Each zone is distinct in the way it consists of sand, shells, and rocks. In the swash, a large proportion of the material is rounded and shaped like a seashell; in the beach face, the sand is deposited on a slope that leads to the beach crest; in the wrack line, the sand particles are smaller than those found in the swash; and in the berm, larger rocks are deposited. Various geomorphic features are also present in some beaches, such as spits and points that form land bridges between islands and mainlands.