Longshore drift

Longshore drift is the transport of sediment along a coast by waves approaching at an angle. Swash moves material diagonally up the shore, while backwash carries it downslope.

Swash: The uprush of water across a beach after a wave breaks. Its oblique path carries sediment up the beach in the direction of wave approach.
Groynes: Shore-perpendicular structures built to interrupt sediment movement along a coast. Groynes trap sediment moving by longshore drift, often widening the updrift beach.
Spit: A narrow ridge of sand or gravel extending from a coast into open water, attached at one end. A spit commonly grows where longshore transport carries sediment beyond a bend or river mouth.
Rip current: A narrow, fast current flowing seaward from the shoreline through the surf zone. Unlike longshore drift, a rip current carries water and sediment offshore rather than along the coast.
Backwash: The return flow of water down a beach after swash. Its downslope flow completes the zigzag movement that transports sediment along the coast.
Breakwater: A structure built offshore or nearshore to reduce wave energy reaching a coast or harbor. By changing waves and currents, breakwaters can alter local longshore sediment transport.
Tombolo: A ridge of sediment connecting an island to a mainland or another island. Alongshore sediment transport can help build the ridge linking land across sheltered water.
Beach drift: The zigzag movement of sediment up and down a beach under angled swash and returning backwash. Beach drift names the shoreward and seaward steps that can produce net longshore transport.
Wave refraction: The bending of waves as different parts of a wave front encounter changing water depths. It changes wave approach angles near headlands and bays, altering alongshore transport.
Beach nourishment: The placement of sand or other sediment on an eroding beach to widen or restore it. Nourished sediment may be redistributed alongshore by the same wave-driven process.

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