Editing Longshore drift (section)

{{short description|Sediment moved by the longshore current}}
{{Use dmy dates|date=October 2024}}
[[File:Longshore i18n.png|thumb|Diagram demonstrating longshore drift:{{Ordered list|beach|sea|longshore current direction|incoming waves|swash|backwash}}]]
 
'''Longshore drift''' from '''longshore [[Current (fluid)|current]]''' is a geological process that consists of the transportation of [[sediment]]s (clay, silt, pebbles, sand, shingle, shells) along a coast parallel to the [[Coast|shoreline]], which is dependent on the angle of incoming wave direction.  Oblique incoming wind squeezes water along the coast, generating a water current that moves parallel to the coast.  Longshore drift is simply the sediment moved by the longshore current. This current and sediment movement occurs within the [[surf zone]]. The process is also known as '''littoral drift'''.<ref>Gomez-Pina G (2002) "Sand dune management problems and techniques, Spain", ''Journal of Coastal Research'', Iss '''36''': 325–332.</ref>

[[Beach sand]] is also moved on such oblique wind days, due to the swash and backwash of water on the beach. Breaking surf sends water up the coast (swash) at an oblique angle and gravity then drains the water straight downslope (backwash) perpendicular to the shoreline.  Thus beach sand can move downbeach in a sawtooth fashion many tens of meters (yards) per day.  This process is called "beach drift", but some workers regard it as simply part of "longshore drift" because of the overall movement of sand parallel to the coast.

Longshore drift affects numerous sediment sizes as it works in slightly different ways depending on the sediment (e.g. the difference in long-shore drift of sediments from a sandy beach to that of sediments from a [[shingle beach]]). Sand is largely affected by the oscillatory force of breaking [[water waves|waves]], the motion of sediment due to the impact of breaking waves and bed shear from long-shore current.<ref name="Reeve et al., 2004">Reeve et al., 2004</ref> Because shingle beaches are much steeper than sandy ones, plunging breakers are more likely to form, causing the majority of longshore transport to occur in the [[swash zone]], due to a lack of an extended surf zone.<ref name="Reeve et al., 2004"/>