Mixing and flushing of tidal embayments in the western Dutch Wadden Sea part I: Distribution of salinity and calculation of mixing time scales

The distribution of salinity in the western Dutch Wadden Sea is described, mainly on the basis of surveys carried out during 1970 to 1974. Relations are discussed between the salinity distribution and relevant environmental factors such as: fresh water discharge, salinity of the North Sea, the tide, the windfield and the morphology of the area. Flushing time scales of 15 and 31 tidal periods were obtained for fresh water originating from the main sluicing gates near Den Oever and Kornwerderzand, respectively Stationary salinity distributions were used for the calculation of exchange coefficients between compartments of a box model of the area. By means of the box model a series of time scale relevant to the flushing of the area has been calculated and their areal distribution is shown. Distinction has been made between ages and transit times of water originating either from one of the two tidal inlets (sea water) or from one of the two sluicing gates (fresh water). Of the former, the ages in the basin (11.3 and 12.3 T) exceed the transit times (2.7 and 3.0 T) whereas the opposite is found for fresh water (ages 10.6 and 19.8 T, transit times 14.5 and 29.1 T). Turn-over times of the main tidal basins were also calculated, the result being 13.7 T for the Marsdiep basin and 9.0 T for the Vlie basin.