Longshore drift

[2] The concept of longshore drift or transportation of sediment parallel to the shore by wave action has evolved considerably with time.

While such early perceptions were imprecise, this evolution has encouraged a gradually more sophisticated understanding of the processes occurring at coastlines.

Erosion of coasts and sediment transport was known in ancient times, mostly in those parts of the world where dramatic changes of shores take place.

Fishermen, sailors and locals would note that sand and gravel seemingly "moved" down the beaches; they didn't fully understand the mechanics, however.

The most common factors taken into consideration in these formulas are: Longshore drift plays a large role in the evolution of a shoreline, as if there is a slight change of sediment supply, wind direction, or any other coastal influence longshore drift can change dramatically, affecting the formation and evolution of a beach system or profile.

The proximal end is constantly attached to land (unless breached) and may form a slight “barrier” between the sea and an estuary or lagoon[8] (called peresyp in the Russian tradition of geomorphology).

[8] As an example, the New Brighton spit in Canterbury, New Zealand, was created by longshore drift of sediment from the Waimakariri River to the north.

[10] This system has undergone numerous changes and fluctuations due to avulsion of the Waimakariri River (which now flows to the north of Banks Peninsula), erosion and phases of open marine conditions.

[10] The majority of tidal inlets on longshore drift shores accumulate sediment in flood and ebb shoals.

[4] Tidal inlets can act as sinks and sources for large amounts of material, which therefore impacts on adjacent parts of the coastline.

Arcachon lagoon in southwest France is an example of a tidal inlet system, which provides large sources and sinks for longshore drift sediments.

Groynes are shore protection structures, placed at equal intervals along the coastline in order to stop coastal erosion and generally cross the intertidal zone.

[2] Due to this, groyne structures are usually used on shores with low net and high annual longshore drift in order to retain the sediments lost in storm surges and further down the coast.

Detached breakwaters are shore protection structures, created to build up sandy material in order to accommodate drawdown in storm conditions.

[2] The major influence, which the creation of a port or harbour can have on longshore drift, is the alteration of sedimentation patterns, which in turn may lead to accretion and/or erosion of a beach or coastal system.

[2] As an example, the creation of a port in Timaru, New Zealand in the late 19th century led to a significant change in the longshore drift along the South Canterbury coastline.