The influence of ambient current on waves

Waves are subject to the influence of ambient current, when they propagate on it. The ambient current can be tidal current, ocean current, local wind generated current, river current and wave generated current. It has been observed that current affects the growth and decay of waves (Yu, 1952; Hedges et al., 1985; Lia et al., 1989). The observations have shown that in a strong opposite current the wave steepness and wave height increase significantly. These changes take place rapidly where the waves are blocked by the current, often accompanied with current-induced whitecapping and wave reflections. Moreover, at the blocking frequency action is also partially transferred away from the blocking frequency to higher and lower frequencies by nonlinear wave-wave interactions (Ris, 1997).


It was Longuet-Higgins and Stewart (1960, 1961, 1962) who founded the theoretical description of wave-current interactions. Since then, many additional results of wave-current interactions have been published. If waves propagate in the presence of ambient current, action density is conserved whereas energy density is not. Therefore, in SWAN the action balance equation has been adopted.