A beach is a narrow strip of loose sediment, such as sand or gravel, that borders a body of water. The sediment may be the result of erosion or deposition. Beaches can be found along oceans, seas, lakes and rivers. They are very popular with people who want to swim and sunbathe. Beaches also serve as economic and cultural hubs for local communities, with hotels, restaurants and bars located nearby.
A wide range of materials can be found on a beach, including sand, pebbles, shell fragments and even rock. Many of these materials are the result of erosion. Waves pounding a rocky coast, for example, can wear away rocks and erode sediments until huge boulders are reduced to tiny grains of sand. Beaches can also be built from sediment deposited by currents. These sediments may come from a river or the seafloor, or they may be washed from other beaches by surf.
The composition of a beach depends on the type and amount of sediments upstream, and on the speed of flow and turbidity of the water or wind. In general, sandy beaches tend to be more erodable than rocky coastlines, and are shaped by the nature and intensity of waves that hit them. Beaches can be built and destroyed within a day, as the tide and weather move sediment from one place to another.
When a beach is under constant attack by waves, erosion will eventually take over and reduce the width of the beach. This is known as beach recession. If the beach is protected by a protective barrier, such as dunes or a cliff, erosion will be much less severe and the beach will gradually grow wider. Beaches that are heavily populated by humans will experience more rapid erosion than those that are uninhabited, as the presence of buildings, roads, hotels and other structures increases the turbidity of the water and slows down the flow of sediment.
Beaches are very dynamic, constantly changing in shape and composition. The most common types of beach breaks are spilling waves, surging waves and plunging waves. The characteristics of these different types of waves are determined by the topography and composition of a particular beach, as well as its proximity to sandbars created by currents, storms or dredges.
Many factors can affect the shape of a beach, and its ability to accrete and build. Vegetation on a beach can be an important stabilizing force, as it absorbs the energy of waves and reduces their erosive power. In addition, the roots of certain types of plants can help to hold the soil together. Unfortunately, human activity such as urban development, dam projects and rerouting of rivers can also decrease the availability of sediment that would normally be carried by waves and deposited along coastlines. This can lead to the loss of beach width, and a reduction in the size and strength of waves. Beaches can be stabilized by planting shrubs and trees.