Editing Longshore drift (section)

==Overview==

===Longshore drift formulas===
Numerous calculations take into consideration the factors that produce longshore drift.
These formulations are:
#Bijker formula (1967, 1971)
#The Engelund and Hansen formula (1967)
#The Ackers and White formula (1973)
#The Bailard and Inman formula (1981)
#The Van Rijn formula (1984)
#The Watanabe formula (1992)<ref name="autogenerated1">Bijker, E.W., 1971. Longshore transport computation. J. Waterways Harbors Division 97, WW4, 687—701.</ref>

These formulas provide a different view of the processes that generate longshore drift. The most common factors taken into consideration in these formulas are:
*[[Suspension (chemistry)|Suspended]] and [[bed load]] transport
*Waves, e.g., breaking and non-breaking
*The [[Shear (fluid)|shear]] exerted by waves or the [[Fluid dynamics|flow]] associated with waves.<ref name="autogenerated1"/>

===Features of shoreline change===
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. These changes do not occur due to one factor within the coastal system, in fact there are numerous alterations that can occur within the coastal system that may affect the distribution and impact of longshore drift. 
Some of these are:

#	Geological changes, e.g. erosion, backshore changes and emergence of headlands.
#	Change in hydrodynamic forces, e.g. change in wave diffraction in headland and offshore bank environments.
#	Change to hydrodynamic influences, e.g. the influence of new tidal inlets and deltas on drift.
#	Alterations of the sediment budget, e.g. switch of shorelines from drift to swash alignment, exhaustion of sediment sources.
#	The intervention of humans, e.g. cliff protection, groynes, detached breakwaters.<ref name="Reeve et al., 2004"/>

===The sediment budget===
The [[sediment budget]] takes into consideration sediment sources and [[Endorheic basin|sinks]] within a [[system]].<ref name="Brunn, 2005">Brunn, 2005</ref> This sediment can come from any source with examples of sources and sinks consisting of: 
*	[[River]]s
*	[[Lagoon]]s
*	Eroding land sources
*	Artificial sources e.g. nourishment
*	Artificial sinks e.g. mining/extraction
*	Offshore transport
*	Deposition of sediment on shore
*      Gullies through the land 
This sediment then enters the coastal system and is transported by longshore drift. A good example of the sediment budget and longshore drift working together in the coastal system is [[inlet]] ebb-tidal shoals, which store sand that has been transported by long-shore transport.<ref name="Brunn, 2005, Michel and Howa, 1997">Brunn, 2005, Michel and Howa, 1997</ref> As well as storing sand these systems may also transfer or by pass sand into other beach systems, therefore inlet ebb-tidal (shoal) systems provide good sources and sinks for the sediment budget.<ref name="Brunn, 2005, Michel and Howa, 1997"/>

[[Sediment deposition]] throughout a shoreline profile conforms to the [[null point hypothesis]]; where gravitational and hydraulic forces determine the settling velocity of grains in a seaward fining sediment distribution. Long shore occurs in a 90 to 80 degree backwash so it would be presented as a right angle with the wave line.