Virtual wave stress and mean drift in spatially damped surface waves

The concept of virtual wave stress (VWS) is applied to spatially attenuated, deepwater surface gravity waves. With particular emphasis on laboratory wave tank measurements it is pointed out that VWS induces a mean Eulerian drift current that increases with time. This can be important for the determination of the wave‐induced drift current, especially when the surface contains thin slicks of contaminating material. A novel formulation is derived that relates VWS to the lateral divergence of the mean wave momentum flux. It is suggested that this formulation can be helpful in determining the mean drift current in the presence of surface slicks as well as the mean volume flux associated with deepwater waves that break in a limited spatial region.