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Ocean Dynamics

, Volume 56, Issue 3–4, pp 284–294 | Cite as

Flow velocity profiles in the Lower Scheldt estuary

  • Johan Christian Winterwerp
  • Zheng Bing Wang
  • Theo van der Kaaij
  • Kristof Verelst
  • Arnout Bijlsma
  • Youri Meersschaut
  • Marc Sas
Original paper

Abstract

Recent acoustic Doppler current profiler (ADCP)-measurements in the Scheldt estuary near Antwerp, Belgium, revealed anomalous, i.e. anti-clockwise circulations in a left bend during the major part of the flood period; these circulations were established shortly after the turn of the tide. During ebb, anti-clockwise circulations persisted, as predicted by classical theory. These data were analysed with a 3D and a 1DV-model. The 3D simulations reveal that the anomalous circulations are found when salinity is included in the computations—without salinity “normal” circulations were found. From analytical and 1DV simulations, it is concluded that a longitudinal salinity gradient \({\partial S} \mathord{\left/ {\vphantom {{\partial S} {\partial x}}} \right. \kern-\nulldelimiterspace} {\partial x}\) may induce a near-bed maximum in flow velocity reversing the direction of the secondary currents. The 1DV-model was then used to assess the contribution of various processes one by one. It was found that because of a reduction in vertical mixing, the vertical velocity profile is not at equilibrium during the first phase of accelerating tide, further enhancing the effects of \({\partial S} \mathord{\left/ {\vphantom {{\partial S} {\partial x}}} \right. \kern-\nulldelimiterspace} {\partial x}\). A small vertical salinity gradient \({\partial S} \mathord{\left/ {\vphantom {{\partial S} {\partial z}}} \right. \kern-\nulldelimiterspace} {\partial z}\) appeared to have a very large effect as the crosscurrents of the secondary circulations induced by \({\partial S} \mathord{\left/ {\vphantom {{\partial S} {\partial x}}} \right. \kern-\nulldelimiterspace} {\partial x}\) became an order of larger magnitude. However, at the site under consideration, the effects of transverse salinity gradients, generated by differential advection in the river bend, were dominant: adverse directions of the secondary circulations were found even when the vertical velocity profile became more regular with a more or less logarithmic shape, i.e. when the effects of \({\partial S} \mathord{\left/ {\vphantom {{\partial S} {\partial x}}} \right. \kern-\nulldelimiterspace} {\partial x}\) and \({\partial S} \mathord{\left/ {\vphantom {{\partial S} {\partial z}}} \right. \kern-\nulldelimiterspace} {\partial z}\) did not play a dominant role anymore. It is argued that data on the secondary velocity structure, which can be measured easily owing to today’s developments in ADCP equipment, may serve as an indicator for the accuracy at which the salinity field is computed with 3D numerical models. Moreover, the large effect of the salinity structure on the velocity field must have a large impact on the morphological development of estuaries, which should therefore be accounted for in morphological modelling studies.

Keywords

River bends Secondary currents Gravitational circulation Estuarine morphology 

Notes

Acknowledgement

We would like to thank “Het Ministerie van de Vlaamse Gemeenschap” (Ministry of the Flemish Community) for financing this study and their approval to publish the results.

References

  1. Chatwin PC (1976) Some remarks on the maintenance of the salinity distribution in estuaries. Estuar Coast Mar Sci 4:555–566CrossRefGoogle Scholar
  2. Chant RJ (2002) Secondary circulation in a region of flow curvature: relationship with tidal forcing and river discharge. J Geophys Res 107(C9):14/1–14/11CrossRefGoogle Scholar
  3. Chant RJ, Wilson RE (1997) Secondary circulation in a highly stratified estuary. J Geophys Res 102(C10):23,207–23,215CrossRefGoogle Scholar
  4. De Vriend HJ (1981) Steady flow in shallow channel bends, Ph.D. Thesis, Delft University of TechnologyGoogle Scholar
  5. Dronkers J (1996) The influence of buoyancy on traverse circulation and on estuarine dynamics. In: Aubrey DG, Friedrichs CT (eds) Buoyancy effects on coastal and estuarine dynamics. AGU, Washington, pp 341–356Google Scholar
  6. Dyer KR (1977) Lateral circulation effects in estuaries, in: estuaries, geophysics and the environment. National Academy of Sciences, Washington 2:22–29Google Scholar
  7. Dyer KR (1997) Estuaries—a physical introduction. Wiley, ChisesterGoogle Scholar
  8. Geyer WR (1993) Three-dimensional tidal flow around headlands. J Geophys Res 98(C1):955–966CrossRefGoogle Scholar
  9. Hansen DV, Rattray M (1965) Gravitational circulation in straits and estuaries. J Mar Res 23(2):1–4–122Google Scholar
  10. Kalkwijk JPTh, Booij R (1986) Adaptation of secondary flow in nearly horizontal flow. J Hydraul Res 24(1):19–37CrossRefGoogle Scholar
  11. Kranenburg C (1996) Density currents, course notes b81. Delft University of Technology, Faculty of Civil Engineering and Geosciences, The NetherlandsGoogle Scholar
  12. Lacy JR, Monismith SG (2001) Secondary currents in a curved, stratified, estuarine channel. J Geophys Res 106(C12):31,283–31,302CrossRefGoogle Scholar
  13. Lesser GR, Roelvink JA, van Kester JATM, Stelling GS (2004) Development and validation of a three-dimensional morphological model. Coast Eng 51(8–9):883–915CrossRefGoogle Scholar
  14. Prandle D (1982) The vertical structure of tidal currents and other oscillatory flows. Cont Shelf Res 1(2):191–207CrossRefGoogle Scholar
  15. Struiksma N, Olesen KW, Flokstra C, De Vriend HJ (1985) Bed deformation in curved alluvial channels. J Hydraul Res 23(1):57–79CrossRefGoogle Scholar
  16. Valle-Levinson A, Reyes C, Sanay R (2003) Effects of bathymetry, friction and rotation on estuary-ocean mixing. J Phys Oceanogr 33(11):2375–2393CrossRefGoogle Scholar
  17. Van de Kreeke J, Zimmerman JTF (1990) Gravitational circulation in well- and partially-mixed estuaries, in Ocean Engineering Science. In: Le Méhauté B, Hanes DM (eds) The Sea. Wiley–Interscience, New York 14(A):495–521Google Scholar
  18. Verbeek H, Wang ZB, Thoolen PMC (1999) Secondary currents in estuarine morphodynamic modeling, a case-study of the Western Scheldt, IAHR symposium on river, coastal and estuarine morphodynamics, Genova, 1999, pp 649–658Google Scholar
  19. Winterwerp JC (2001) Stratification effects by cohesive and non-cohesive sediment. J Geophys Res 106(C10):22,559–22,574CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • Johan Christian Winterwerp
    • 1
    • 2
  • Zheng Bing Wang
    • 2
    • 3
  • Theo van der Kaaij
    • 2
  • Kristof Verelst
    • 4
  • Arnout Bijlsma
    • 2
  • Youri Meersschaut
    • 6
  • Marc Sas
    • 5
  1. 1.Delft University of Technology, Environmental Fluid MechanicsDelftThe Netherlands
  2. 2.WL|Delft HydraulicsDelftThe Netherlands
  3. 3.Delft University of Technology, Hydraulic EngineeringDelftThe Netherlands
  4. 4.Flanders Hydraulics ResearchAntwerpBelgium
  5. 5.IMDCAntwerpBelgium
  6. 6.Flanders Hydraulics LaboratoryAntwerpBelgium

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