A beach is a narrow strip of land that lies along the edge of a body of water, such as an ocean or a lake. It is made up of loose, sometimes granular, material such as sand or pebbles. It is a dynamic environment that constantly changes with erosion and other natural processes, but also as a result of human activities such as building development, storms, pollution and other disturbances. Beaches are found around the world, and are very important to ecosystems because they can provide habitat for marine life, and be a source of recreation and tourism.
Beaches are usually located adjacent to seas or lakes, but they can also be found on rivers. They are typically composed of unconsolidated materials such as sand, gravel and other sediments, but may also contain rock fragments or biological matter such as coral. They are formed primarily by wave action, and their characteristics change rapidly depending on the location, geological history and sediment sources of a beach.
The term beach is generally used to refer to a coastal zone that extends from the low tide line or shoreline to a point of significant landward change in topographic form, such as a dune, cliff or man-made structure such as a seawall. The zone is often divided into two parts, the beach face and the backshore. The beach face is a sandy, intertidal area that is usually covered by water during high tides and at times by a protective dune or berm (often referred to as the beach ridge).
The backshore is a dry, often windswept area above the low tide line. It is the site of an embryonic dune or spit, and can be a feature of a barrier island, barrier spit, dune peninsula or baymouth barrier. It is shaped by erosion of rocks offshore, slumping of headland cliffs and sand deposition from longshore drift. Some sand particles are created by sand-diffusion from nearby beaches, and some are created by grazing by fish that nibble on algae attached to rocks and coral in the water.
Beaches can be very polluted, especially in urban areas, as a result of waves washing up raw sewage and other toxic chemicals that have been spilled or washed from inland sources. In addition, many beaches are impacted by the debris that is washed ashore by strong storms, such as plastic bags and other containers from picnics, medical waste from hospitals and even car batteries and tires. Finally, the removal of beach flora by people for residential and commercial construction can greatly affect the shape of the dunes and the underlying sediments, causing erosion and exposing the sand to further wash by surf and wind. In some cases, the beach erosion is addressed by practices such as beach nourishment. However, even when these measures are taken, human impacts to beaches tend to be temporary. Freak wave events and other climatological influences can substantially alter the shape and location of a beach within hours.