A beach is a landform alongside a body of water, consisting of loose particles (such as sand, gravel, pebbles, shells and coralline algae) that are shaped and maintained by wave action. The characteristics of beaches vary considerably and are influenced by a range of factors, from the nature and quantity of the sediments deposited to the speed and turbidity of the wind and water. Beaches typically undergo rapid seasonal changes during the winter storms, monsoons and hurricanes.
Beaches have a wide range of social, economic and cultural functions. In many places they are extensively used for recreation (swimming, sunbathing, playing sports, etc.), and may have facilities such as lifeguard posts, changing rooms, showers, shacks, and restaurants. Many beaches play an important role in the conservation of natural resources, including sea grass beds and marine fauna.
Beach sand is typically light in color, with a high silica content, and can come from geologic sources (such as adjacent rocky coastlines) or biological ones, such as fragments of mollusc shells or reef organisms. The sand on a beach is sorted by size and density by the movement of waves and currents, which tend to transport lighter, less-dense sand grains, leaving heavier ones behind. The sand on a beach also varies in its composition, which can depend on the amount of nearby material, such as rock and other debris, that is eroded by waves.
In addition to the erosion of the shoreline, waves and currents can envelop a beach, forming a lagoon or delta. The sediment in these engulfed areas can change the character of coastal shallows, eroding or depositing sand in areas that were once marshy or reed-dominated. In some cases, the reclaimed sand is used for building materials or for beach nourishment, which involves importing and depositing sediment to restore a deteriorating beach.
A beach is usually characterized by its frontal beach terrace surface, which is inclined slightly seaward, and a lower back beach slope or face. The beach profile varies seasonally, with a greater intensity of wave action during summer and a lesser intensity in the winter. The shape of the beach ridges and dunes, which are elevated above the level of the water by the action of waves and onshore winds, can also vary during different seasons. The structure of a beach is greatly influenced by the vegetation growing on it, especially those plants with complex network root systems. These plants help to stabilize the foredunes and prevent the inland movement of dunes during strong winds and freak waves. The diversion of freshwater runoff into drains deprives these plants of their water supply and exposes them to salt water incursion, which can kill them.