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 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. Alongshore gradients in wave set-up also contribute to the longshore current.

For further explanations, see Shallow-water wave theory#Longshore Currents.

An empirical formula for the longshore current [math]V[/math] halfway the surf zone is

[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 root-mean-square 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. Prentice-Hall, 544pp.