Dispersion of Buoyant Material by Langmuir Circulation and a Tidal Current

An analytical model is developed which quantifies and describes the dispersion of buoyant material caused by wind and wave generated Langmuir circulation in a tidal flow. It is found that the angle between the orientation of the Langmuir bands, taken to be in the wind direction, and the current controls the lateral (across-current) dispersion. Largest values of the dispersion occur when the wind and current are almost perpendicular and the wind is strong relative to the current. The lateral diffusivity caused by Langmuir circulation is compared with that produced by a current alone, and it is shown that the dispersive effects of Langmuir circulation will usually dominate when the wind speed exceeds about 50 times the current.