Water Surface Velocities Induced by Wind Shear

A theoretical model is developed for calculating the water surface drift velocity which arises when, in the absence of water surface waves, a turbulent shear stress is exerted by wind on the surface of an originally standing body of water. Solutions are given for steady flow in both air and water, for the asymptotic cases of very long fetches (flow along a channel of water) and very short fetches (offshore wind onto deep water). As long as the flow in the water remains laminar, the drift velocity is correctly predicted by the theory and is found to agree with experimental results of Keulegan (4) and Plate, et.al. (10). For turbulent flows, the fetch dependency of the surface velocity is correctly predicted, but the model fails to properly account for the dependency of the drift velocity on the average parameters of the air flow.