Longshore current
Definition of Longshore current:
Current running parallel to the shore generated by obliquely incident waves.
This is the common definition for Longshore current, other definitions can be discussed in the article

Notes
The longshore current is mainly generated by the shoreparallel component of the stresses associated with the breaking process of obliquely incoming waves, the socalled radiation stresses. It is generally a fluctuating and meandering current that dominates in the surf zone. Other, generally smaller components of the longshore current are: currents driven by alongshore gradients in wave setup and currents driven by tide and wind.
For further explanations, see Shallowwater wave theory#Longshore Currents and Littoral drift and shoreline modelling.
An empirical formula for the longshore current [math]V[/math] halfway the surf zone is^{[1]}
[math]V = 1.17 \sqrt{g H_b} \sin \theta_b \cos \theta_b ,[/math]
where [math]g[/math] is the gravitational acceleration ([math]\approx 9.8 m^2/s[/math]), [math]H[/math] the rootmeansquare wave height and [math]\theta[/math] the wave incidence angle. These quantities are evaluated at the depth of incipient wave breaking indicated by the subscript [math]_b[/math].
Recommended review article:
 Hanes, D.M. 2022. Longshore Currents. Treatise on Geomorphology, 2nd edition, Chapter 8.04. Elsevier.
Recommended book:
 Komar, P.D. 1998. Beach Processes and Sedimentation. Second edition. PrenticeHall, 544pp.
References
 ↑ Komar, P.D. 1979. Beachslope dependence of longshore currents. Journal of the Waterway, Port, Coastal and Ocean Division 105(4): 460–464