The current generated by deep water regular waves

Second-order mean drift of wave particles can in deep water be calculated using potential theory, resulting in the well-known Stokes drift. Potential theory assumes an ideal, incompressible and irrotational flow, which according to Longuet-Higgins [8] is not permanent. In this document it is recommended, for rotational flow, to add a current term to Stokes wave equations. This is based on the argument that a change in wave number is due to the onset of a current.