Abstract
A 3D unstructured-grid numerical model of the Ems Estuary is presented. The simulated hydrodynamics are compared against tidal gauge data and observations from research cruises. A comparison with an idealized test reveals the capability of the model to reproduce the secondary circulation patterns known from theoretical results. The simulations prove to be accurate and realistic, confirming and extending findings from earlier observations and modeling studies. The basic characteristics of dominant physical processes in the estuary such as tidal amplification, tidal damping, overtide generation, baroclinicity and internal mixing asymmetry are quantified. The model demonstrates an overall dominance of the flood currents in most of the studied area. However, the hypsometric control in the vicinity of Dollart Bay reverses this asymmetry, with the ebb currents stronger than the flood ones. Small-scale bathymetric characteristics and baroclinicity result in a very complex interplay between dominant physical mechanisms in different parts of the tidal channels and over the tidal flats. Residual flow reveals a clear overturning circulation in some parts of the estuary which is related to a mixing asymmetry between flood and ebb currents. We demonstrate that while areas close to the tidal river exhibit overall similarity with density controlled estuarine conditions, in large areas of the outer estuary barotropic forcing and complex bathymetry together with the density distribution affect substantially the horizontal circulation.
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Acknowledgments
We want to thank Thomas Badewien for providing the observational data. Huib de Swart, Henk Schuttelaars and Arnoldo Valle-Levinson gave very helpful comments regarding the theory of estuarine flows. Aron Roland contributed to this study with practical help in the computational domain. The bathymetric data were provided by the Bundesamt fuer Seeschifffahrt und Hydrographie (BSH). The gridded model topography was prepared in Helmholtz-Centrum Geesthacht. Some simulations used in this paper were conducted using the following computational facilities: (1) Sciclone at the College of William and Mary which were provided with the assistance of the National Science Foundation, the Virginia Port Authority, and Virginia’s Commonwealth Technology Research Fund; (2) the Extreme Science and Engineering Discovery Environment (XSEDE; Grant TG-OCE130032), which is supported by National Science Foundation grant number OCI-1053575; (3) NASA’s Pleiades.
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Pein, J.U., Stanev, E.V. & Zhang, Y.J. The tidal asymmetries and residual flows in Ems Estuary. Ocean Dynamics 64, 1719–1741 (2014). https://doi.org/10.1007/s10236-014-0772-z
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DOI: https://doi.org/10.1007/s10236-014-0772-z