Influence of currents on equilibrium range spectra of wind waves

It is well known that water waves tend to be higher or lower as they propagate onto an opposing or following current, respectively. This is also true for wind waves generated on currents. In the equilibrium range of wind waves, however, the spectral densities for the waves generated on a following or opposing current are larger and smaller, respectively, than those for the waves generated on quiescent water. To see this, a series of laboratory experiments was carried out in a wind-wave and current flume for various conditions of water depth, current, and wind. The experimental results qualitatively confirm the theoretical equations proposed by Gadzhiyev et al. in 1978 and Suh et al. in 1994, with the former performing marginally better for following currents and the latter doing better for opposing currents. It is also shown that the partially developed laboratory waves fall under gravity waves so that the laboratory regime represents the open ocean situation.