A beach is a sheltered, sandy shoreline where people swim, sun and play. Beaches are popular recreational areas and many have associated facilities such as lifeguards, changing rooms, showers, shacks and restaurants. Beaches also provide important natural functions such as erosion control and flood protection.
A coastal area that is dominated by beaches is known as a beach community. Beach communities typically include residential, commercial and hospitality venues as well as salt marshes and freshwater wetlands that are important habitats for birds and other species.
Sediments that form a beach are usually sand, although they can be any granular material the waves and currents have access to and can shift around (such as soil, silt, gravel, cobble or shingle). The size of the particles in the sediment influences how easily it is moved by waves and currents. For example, large rock fragments tend to be moved by the sea more easily than sand. Beaches influenced by very energetic winds and waves are more likely to have coarse, pebble-sized sediments, as these resist the force of the breaking wave a longer time than finer material.
The beach crest is the part of the beach that is above water at high tide, while the beach face, tidal flats and longshore drift are all below water. The beach berm is the zone of unconsolidated sediment between the crest and the line where wave run-up is no longer possible.
Beach flora has a significant effect on the shape of the beach, especially dunes. Plants with dense network roots can slow fluid flow and help prevent lateral movement of the dune. They may also trap sand particles and enrich the surface layer, so other plants can grow.
Wave-generated sand bars are a common feature of beaches. These are ridges of sand or pebbles that extend offshore and are stabilized by longshore drift, the convergence of ocean currents, wind direction, tidal movements and oblique incident waves.
In contrast, barrier islands are ridges of sand that are backed by mangrove forests and other low-lying vegetation and that rise to form protective lagoons. These are influenced by a combination of wind, waves and tides.
Beaches often have a variety of hazards and threats, including erosion and pollution. Pollution from urban areas is a particular problem, as it washes toxic chemicals into the sea. In addition, bacteria and raw sewage can wash up on beaches after strong storms. In some cases, beaches are closed after heavy rains, because of the danger of bacterial contamination.