# 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 shore-parallel component of the stresses associated with the breaking process of obliquely incoming waves, the so-called 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 set-up and currents driven by tide and wind.

For further explanations, see Shallow-water wave theory#Longshore Currents and Littoral drift and shoreline modelling.

An empirical formula for the longshore current $V$ halfway the surf zone is[1]

$V = 1.17 \sqrt{g H_b} \sin \theta_b \cos \theta_b ,$

where $g$ is the gravitational acceleration ($\approx 9.8 m^2/s$), $H$ the root-mean-square wave height and $\theta$ the wave incidence angle. These quantities are evaluated at the depth of incipient wave breaking indicated by the subscript $_b$.

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. Prentice-Hall, 544pp.

## References

1. Komar, P.D. 1979. Beach-slope dependence of longshore currents. Journal of the Waterway, Port, Coastal and Ocean Division 105(4): 460–464