EM 1110-2-1100 (Part II)
31 July 2003
Nearshore circulation systems
b. Longshore current.
(1) Wave- and wind-induced longshore currents flow parallel to the shoreline and are strongest in the
surf zone, decaying rapidly seaward of the breakers. These currents are generated by gradients in momentum
flux (radiation stress) due to the decay of obliquely incident waves and the longshore component of the wind.
Typically, longshore currents have mean values of 0.3 m/sec or less, but values exceeding 1 m/sec can occur
in storms. The velocities are relatively constant over depth (Visser 1991).
(2) The concept of radiation stress was first applied to the generation of longshore currents by Bowen
(1969a), Longuet-Higgins (1970a,b), and Thornton (1970). These studies were based on the assumptions of
longshore homogeneity (Figure II-4-14a) and no wind forcing, reducing Equation II-4-35 to a balance
Surf Zone Hydrodynamics