Wassertransport und Wasseraustausch im nordfriesischen Wattenmeer — Ergebnisse numerischer Untersuchungen

Abstract

A three-dimensional baroclinic circulation model and a Lagrangian dispersion model are presented which were used to compute water transports and mixing times in sub-areas of the North Frisian Wadden Sea. Both models were used to simulate tide-induced water motions forced by the principal lunar semidiurnal tide M2, and two selected periods taking into account current meteorological and thermodynamic conditions. Wind speeds were low during the simulation period in summer 1994, while gale-force winds prevailed during the winter 1994 simulation period. The circulation model was used for determining water transports across selected transects in the Wadden Sea. For sub-areas of the Wadden Sea, flushing times were computed on the basis of water transports and volumes of the sub-areas. For a first rough estimate, turnover times were derived from a fixed percentage of the tidal prism. More precise data for the turnover times were determined by means of the dispersion model. When comparing the mixing times computed by different methods, only partial correspondence was found. Parameterization of the turnover time by means of the tidal prism was found to produce some unrealistic results. The turnover times computed with the dispersion model for the summer period ranged between 1 and 7 tidal periods in most sub-areas of the North Frisian Wadden Sea. During the simulation period in winter, both water transports and turnover times deviated substantially from the data of the other case studies.