Processes that shape the shore features of coastlines and begin the mixing, sorting, and transportation of sediments and runoff from land. In particular, the processes include those interactions among waves, winds, tides, currents, and land that relate to the waters, sediments, and organisms of the nearshore portions of the continental shelf. The nearshore extends from the landward limit of storm-wave influence, seaward to depths where wave shoaling begins. See also Coastal landforms.
The energy for nearshore processes comes from the sea and is produced by the force of winds blowing over the ocean by the gravitational attraction of Moon and Sun acting on the mass of the ocean, and by various impulsive disturbances at the atmospheric and terrestrial boundaries of the ocean. These forces produce waves and currents that transport energy toward the coast. The configuration of the landmass and adjacent shelves modifies and focuses the flow of energy and determines the intensity of wave and current action in coastal waters. Rivers and winds transport erosion products from the land to the coast, where they are sorted and dispersed by waves and currents.
In temperate latitudes, the dispersive mechanisms operative in the nearshore waters of oceans, bays, and lakes are all quite similar, differing only in intensity and scale, and are determined primarily by the nature of the wave action and the dimensions of the surf zone. The most important mechanisms are the orbital motion of the waves, the basic mechanism by which wave energy is expended on the shallow sea bottom, and the currents of the nearshore circulation system that produce a continuous interchange of water between the surf zone and offshore areas. The dispersion of water and sediments near the coast and the formation and erosion of sandy beaches are some of the common manifestations of nearshore processes.
Erosional and depositional nearshore processes play an important role in determining the configuration of coastlines. Whether deposition or erosion will be predominant in any particular place depends upon a number of interrelated factors: the amount of available beach sand and the location of its source; the configuration of the coastline and of the adjoining ocean floor; and the effects of wave, current, wind, and tidal action. The establishment and persistence of natural sand beaches are often the result of a delicate balance among a number of these factors, and any changes, natural or anthropogenic, tend to upset this equilibrium. See also Depositional systems and environments; Erosion.
