Beach sand originates mainly from rivers and streams which carry it directly to the ocean. Sand also comes from the gradual weathering of exposed rock formations and cliffs along the shore, and from the deterioration of shell, coral, and other skeletal fragments. Wave action, wind, and currents move sand up and down the coast. This movement is called longshore transport. Sand is also moved onshore and offshore by waves, tides, and currents. During storms, high-energy waves often erode sand from the beach and deposit it offshore as submerged sandbars. This sand is then moved back onshore by low-energy waves in periods of calm weather. Sand that is moved offshore by winter storms, leaving steep narrow beaches, is returned to the shore by the gentle waves of summer, creating wide, gently sloping beaches.
Erosion and accretion of sediment on coasts are natural processes influenced by the beach slope, sediment size and shape, wave energy, tides, storm surge, and nearshore circulation, among other things. Human activities such as dredging, river modification, removal of backshore vegetation, and installation of protective structures such as breakwaters can profoundly alter shorelines, mainly by affecting the sediment supply.
Changes to our shorelines affect our transportation routes, our communities, and our ecosystems; therefore, it is important to monitor them. Researchers can determine shoreline locations with information gathered from topographic maps, aerial photos, Global Positioning System (GPS) surveys, and beach profiles. By analyzing trends over time, future changes can be predicted. Planners and developers can use the predictions for planning future use of the shoreline.