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Ocean Dynamics

, Volume 59, Issue 2, pp 239–262 | Cite as

Modeling the impact of wind and waves on suspended particulate matter fluxes in the East Frisian Wadden Sea (southern North Sea)

  • Karsten A. LettmannEmail author
  • Jörg-Olaf Wolff
  • Thomas H. Badewien
Article

Abstract

Suspended particulate matter (SPM) fluxes and dynamics are investigated in the East Frisian Wadden Sea using a coupled modeling system based on a hydrodynamical model [the General Estuarine Transport Model (GETM)], a third-generation wave model [Simulating Waves Nearshore (SWAN)], and a SPM module attached to GETM. Sedimentological observations document that, over longer time periods, finer sediment fractions disappear from the Wadden Sea Region. In order to understand this phenomenon, a series of numerical scenarios were formulated to discriminate possible influences such as tidal currents, wind-enhanced currents, and wind-generated surface waves. Starting with a simple tidal forcing, the considered scenarios are designed to increase the realism step by step to include moderate and strong winds and waves and, finally, to encompass the full effects of one of the strongest storm surges affecting the region in the last hundred years (Storm Britta in November 2006). The results presented here indicate that moderate weather conditions with wind speeds up to 7.5 m/s and small waves lead to a net import of SPM into the East Frisian Wadden Sea. Waves play only a negligible role during these conditions. However, for stronger wind conditions with speeds above 13 m/s, wind-generated surface waves have a significant impact on SPM dynamics. Under storm conditions, the numerical results demonstrate that sediments are eroded in front of the barrier islands by enhanced wave action and are transported into the back-barrier basins by the currents. Furthermore, sediment erosion due to waves is significantly enhanced on the tidal flats. Finally, fine sediments are flushed out of the tidal basins due to the combined effect of strong erosion by wind-generated waves and a longer residence time in the water column because of their smaller settling velocities compared to coarser sediments.

Keywords

Suspended particulate matter fluxes Wadden Sea Tidal flat Surface gravity waves  Storm surges Numerical modeling 

Notes

Acknowledgements

This model study was highly dependent on external data sources. Therefore, we are grateful to Ralf Berger from the Federal Maritime and Hydrographic Agency (BSH, Bundesamt für Seeschifffahrt und Hydrographie) for providing the wave data from the wave buoys in the German Bight; Heike Gentz and Michael Hesse from BSH and Ralf Kaiser from NLWKN (Niedersächsischer Landesbetrieb für Wasserwirtschaft, Küsten- und Naturschutz) for bathymetric data; and, finally, Adam Kubicki (Forschungsinstitut Senckenberg, Department of Marine Science) for providing us with wave data from the time-series station. Furthermore, we want to mention the helpful discussions with Alexander Bartholomä, Burghard Flemming, Jöran März, Ulf Gräwe, Joanna Staneva, and Emil Stanev. Last but not least, we thank two anonymous reviewers, whose thoughtful comments helped to improve the quality of the manuscript. This study was embedded within the research group ’Biogeochemistry of tidal flats’, which was funded by the Deutsche Forschungsgemeinschaft (DFG).

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Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Karsten A. Lettmann
    • 1
    Email author
  • Jörg-Olaf Wolff
    • 1
  • Thomas H. Badewien
    • 2
  1. 1.Institute for Chemistry and Biology of the Sea (ICBM), Department of Physical Oceanography (Theory)Carl von Ossietzky University OldenburgOldenburgGermany
  2. 2.Institute of Physics, Department of Marine PhysicsCarl von Ossietzky University OldenburgOldenburgGermany

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