A Model Study of the Rhine Discharge Front and Downwelling Circulation

Ruddick, KG. Deleersnijder, Eric [UCL] Demulder, T. Luyten, PJ.

The Rhine is the largest river discharge of the North Sea, and has considerable ecological importance as a source of nutrients and pollutants. While much of the Dutch coastal zone is intensively monitored, it is difficult to perform measurements within the first few km of discharge, a region of very high horizontal and vertical gradients, which influences strongly the fate of freshwater and riverborne material. A fine resolution 3D hydrodynamic model, MU-ROFI, has been developed to simulate the flow in this initial discharge zone. The model is described briefly and a first set of model results is presented and discussed. The process of front formation and associated downwelling on the upstream (with respect to the tide) boundary of the freshwater plume, switching from the South to the North boundary as the tide turns, is illustrated. Qualitative comparison with CTD and airborne remotely sensed measurement indicates that such a behaviour is realistic, at least in conditions of low wind and Neap tide.