A beach is a strip of land along the shoreline of a body of water. While beaches are most often found at the ocean, they can also occur at lakes and rivers. Beaches are characterized by sandy or rocky surfaces, and by a variety of marine and terrestrial life. They are constantly changing, influenced by the forces of waves and currents which move sediment from one place to another.
A beach’s composition depends on the type and quantity of material upstream, the speed and turbidity of water and wind, and the extent to which the sediment is compacted. Sediments are more resistant to erosion when they are consolidated and well vegetated. This is why sand-based beaches typically host dense, often multi-species communities of plants and animals. Beaches are also often covered in seashells, driftwood, logs, and other debris. The Skeleton Coast in Namibia is famous for its accumulation of bones from whales and seals, as well as shipwrecks. Beaches may also be characterized by the presence of human artifacts, such as glass bottles, metal cans, and other refuse.
Waves that break on a beach can shape it by depositing and removing sediment, but they also influence the character of coastal shallows. A beach that receives frequent and large storms, with longshore currents that flow inland, can accumulate finer sediments than sandy or shingle beaches. This can change the character of a beach, making it more like a lagoon or delta.
Beach erosion can be accelerated by human activity, such as clearing the vegetation adjacent to a beach. This changes the surface winds and exposes the beach to more frequent battering by waves. It can also reduce the capacity of wetlands to absorb rainwaters, thereby increasing flooding risk.
Erosion of beaches can expose underlying less resilient materials, such as clay and silt, which then become exposed to wave and wind action. This can lead to the collapse of coastal headlands and the undermining of sea grass beds or coral reefs in the nearshore zone.
Beach nourishment is the practice of pumping sand onto beaches in order to maintain their health and protect buildings and infrastructure located on the beachfront. This is common for major beach cities worldwide and is usually undertaken without the public’s knowledge, as nourished beaches can appear quite natural. For example, many visitors to Waikiki beach would be unaware that the sand is actually trucked in from Manhattan Beach. Beaches that are not regularly nourished can quickly deteriorate and lose their ability to support human activities. As a result, they may be closed to swimming and other water sports, or even completely destroyed by waves and currents. This is especially true of beaches that are located in urban areas, where populations increase and human-driven pressures on the environment intensify. Beaches may also be impacted by climate change, as warmer waters can erode them more rapidly than cooler waters. Beaches also may be subject to nutrient runoff from nearby agricultural areas.