CURRENT STRUCTURE IN THE RHINE REGION OF FRESH-WATER INFLUENCE

Observation with HF radar, ADCPs and conventional current meters in th e Rhine ROFI system in the North Sea indicate that the dominant curren ts are due to tidal flow, with important contributions from winds and density-driven circulation. The tidal currents are dominated by the se midiurnal components, principally the M2, with tidal ellipses parallel to the coast and a semimajor axis of the order of 1 m s(-1) at the su rface. The wind-driven flow varies between 1 and 3% of the wind speed and the rotation varies with depth in qualitative agreement with Ekman theory. After removal of the tidal and wind-driven component the resi dual flow within this region is generally parallel to the coast (north eastward) with average surface speeds of about 10 cm s(-1). A converge nce zone in the surface flow was observed at the outer edge of the coa stal zone. The vertical distribution of residual velocity closely foll ows the Heaps (1972) profile for density-driven flow, with slight devi ations probably due to the tidal rectification (similar to 2 cm s(-1)) .