Coherent vortex structures at the sediment-water interface

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    In river, estuarine and coastal environments, the diffusive boundary layer (DBL) model is typically employed to
    describe solute fluxes between the sediments and the overlying water column. This model assumes that vertical
    diffusion at the sediment-water interface occurs at molecular rates. Recent studies, however, show that measured
    fluxes can be several orders of magnitude larger than can be explained by molecular diffusion alone. Here, we
    use a laboratory experiment to investigate one mechanism for enhanced interfacial fluxes, namely the generation
    of coherent structures at the sediment-water interface. The experiments use a combination of Particle Tracking
    Velocimetry (PTV) and Refractive Index Matching (RIM), thus allowing simultaneous acquisition of
    instantaneous flow fields both above and below the sediment-water interface. The experiments demonstrate the
    existence of coherent structures at the interface and their influence on interfacial exchange. The results show a
    strong dependence of the flow characteristics on the permeability Reynolds number ReK = √KU*/ν. For low ReK
    the flow resembles an impermeable boundary layer, while for high ReK the flow resembles a mixing-layer-type
    flow where the DBL model is no longer applicable. In the high-ReK case, swirl of the instantaneous velocity
    field shows the existence of coherent structures at the interface and these coherent structures extend well into the
    interstitial fluid in the sediment bed. These coherent structures become more pronounced with increasing ReK.
    Original languageEnglish
    Title of host publicationProceedings of the 11th International Symposium on Ecohydraulics
    EditorsJ.A. Webb , J.F. Costelloe , R. Casas-Mulet, J.P. Lyon , M.J. Stewardson
    Place of PublicationMelbourne, Australia
    PublisherUniversity of Melbourne
    Publication statusPublished - 2016
    Event11th International Symposium on Ecohydraulics (ISE) - Melbourne, Australia, Melbourne, Australia
    Duration: 7 Feb 201612 Feb 2016


    Conference11th International Symposium on Ecohydraulics (ISE)


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