A beach is a strip of land along the edge of a body of water (such as lakes, rivers or the world ocean) made up of loose materials like sand, cobbles, pebbles, gravel, and sometimes shells. It can be hundreds of kilometers long or very short and is always moving. Beach material accumulates during periods of accretion and moves away during periods of erosion.
There are several different processes that cause sediments to be deposited on beaches and these include wave action, wind direction, tidal movements, and the erosion of rocks or other natural features. In addition to these natural processes, human activities can have a significant impact on the formation and preservation of beaches. Urban development, dams, and the rerouting of rivers can all reduce the amount of erodible land found near bodies of water which can result in beach recession.
Typically, the area of a beach is divided into four distinct zones known as a beach profile: swash zone, beach face, wrack line and berm. The size of the particles found in each of these zones differs, with sand forming closer to the waterline and smaller particles closer to the landward edge. This is because the movement of waves continuously breaks down and moves sand forward along the beach, while wind carries the sand backwards into dunes or inland to other landforms.
Many people use beaches for recreation and a wide variety of wildlife depends on them. Crabs, birds and sea turtles graze on beach vegetation and sand, while insects, fish and marine plants live in the water or on or under the surface of a beach. Many coastal areas also have a variety of recreational facilities built on or near the beach. Beaches also serve as a source of salt for food preparation and industry.
The most common type of beach is composed of sand, but they can be comprised of any type of loose, sedimentary material. Sediment is generally made up of solid particles that have been fragmented from larger rocks and range in size from clay to boulders. Depending on their origin, different types of sediments may be more or less prone to erode. Beach sand usually contains quartz sand with some smaller fragments of shells, carbonate skeletons or other biological material.
A beach’s location and environment are important factors in determining its stability. A beach with good structural support will have a tendency to accrete, but a beach with poor structure will erode. Freak storms or unusually high tides can substantially alter the shape and composition of a beach within hours.
The erosion and depositional characteristics of a beach are controlled by the amount of erodible sediment available, the movement of water and waves, wind conditions and the type and speed of erosion. In addition, beach nourishment programs can have a significant effect on the condition of a beach. It is therefore important that the placement of new sediments on a beach be done carefully, so that it will have sufficient time to compact and stabilize before more aggressive wave and wind action erodes it.