A beach is a strip of unconsolidated sediment (usually sand, gravel or shingle) adjacent to a body of water. It may be natural or man-made. Beaches are dynamic environments that are constantly changing as waves, tides, and weather erode and deposit material. Beaches also are shaped by human activity such as recreation and tourism, and by a variety of environmental factors including climate, geology and biology.
Many beaches are formed from sand derived from erosion of rock, such as granite or basalt, or from other natural or human-made sources such as sea shells or coralline algae. Other materials found in a beach include organic material, such as twigs and seaweed, and marine organisms such as crabs and mollusc shells. A beach’s coloration is determined largely by the types and amounts of the materials present. Sand can be white, black, tan or yellow, depending on the rocks from which it is derived.
Wave action is the primary factor that erodes and shapes a beach. A beach’s shape can be either constructive or destructive, depending on the direction of the incoming waves and whether they are breaking on the shoreline or rolling into it. Beaches with a greater proportion of constructive wave action tend to have a more gradual slope between the crest and the beach face than beaches with a larger percentage of destructive waves.
When a wave crashes onto a beach, it creates a zone of turbulent water that is called the surf zone or swash zone. This zone can excavate a trough in the beach and carry sand back out to sea on its leeward flank, forming a sandbar. The turbulence of the swash zone can also carry fine-grained sediment such as clay and silt seaward in a process called littoral transport or drift. These finer sediments can be deposited on the beach or carried further offshore, where they can form marshes and lagoons behind barrier islands.
A beach may be protected from the erosion that would otherwise occur by a groyne field, a system of concrete or wood structures that extends out to the water’s edge. Groynes help to stabilize the beach by slowing down the flow of sand and sediment, but are sometimes ineffective in protecting some beaches from severe erosion.
Beaches are a popular site for recreation, and they play an important economic and social role in many communities. These uses often require the construction of beach amenities such as lifeguard stands, restrooms and parking facilities. Some beaches are lined with residential and commercial developments, while others feature shacks and other hospitality venues.
Erosion of beaches can threaten the safety of swimmers and the economic and ecological stability of coastal communities. In addition to changing the appearance and character of a beach, severe erosion can expose less resilient soils and rocks to wind and wave action, leading to their undermining and collapse. Beach erosion can also deprive sea grasses and other marine plants of light and nutrients.