Flemming, Burghard W.

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Flemming, Burghard W.
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Flemming, Burghard W.
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Flemming, Burghard
Flemming, B. W.
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    Item-typ:Veröffentlichung,
    Tide-induced coastal and estuarine suspended sediment transport and equilibrium morphology formation
    (2011-07-18)
    Yu, Qian
    ;
    Huhn, Katrin
    ;
    Flemming, Burghard W.
    ;
    Flemming, Burghard W.
    The tide acts on coastal and estuarine systems, amongst others by inducing (1) sediment transport and, as a consequence, (2) morphological change. The tide-induced behavior of suspended sediment transport has been studied by individually solving the 1D vertical suspended sediment advection-diffusivity equation and the 1D depth-averaged suspended sediment transport equation. The solutions provide a good understanding of two aspects of the problem, namely that (1) the phase lag increases linearly with height above the bed, whereas the amplitude of the SSC variation decreases exponentially with height; and that (2) the relative contributions of local resuspension and advection to depth-averaged suspended sediment concentration can be determined and that the empirical decomposition terms of horizontal residual fluxes of suspended sediment have clear physical explanations. The morphological modeling of back-barrier tidal basins in the Wadden Sea shows that, in equilibrium states, (1) the dimensional parameters of channel area and volume are proportional to the 1.5 power of the basin area and tidal prism, respectively, whereas the dimensionless parameters of relative channel area and the ratio between channel volume and tidal prism are both proportional to the square root of basin area. The values of the coefficients before the power in these relations are of the order of 10-5, and (2) large basin areas and low tidal ranges favor strong concave-up hypsometries, whereas small basin areas and high tidal ranges favor less concave-up hypsometries, which have been interpreted as a response to the relative area of intertidal areas or channels in the tidal basins. The long-term (6,000 years) modeling results of the large funnel-shaped tide-dominated estuarine morphology shows the development of a sand bar that reached equilibrium within about 3,000 years as the leading order characteristics of the estuarine bed. Its general shape, size and position is consistent with historical observations in the Qiangtangjiang Estuary, China. A series of sensitivity analyses suggests that the estuarine convergence rate, sediment supply, and river discharge are the main controlling factors of sand bar formation.
    Dissertation
      636  196
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    Sediment dynamic processes and products on the shoreface of the East Frisian barrier-island system, southern North Sea
    (2009-10-29)
    Son, Chang Soo
    ;
    Hebbeln, Dierk 
    ;
    Flemming, Burghard W.
    ;
    Flemming, Burghard W.
    The investigations on the Otzum ebb-delta were, amongst others, carried out to test the sediment bypassing model postulated in the 1980's and before. To achieve this, sediment distribution patterns, bedform migration (swash bars and dunes) as well as sediment transport directions were determined. The main body of the ebb-tidal delta is composed of fine sands, whereas superimposed swash bars on the inlet shoals consist of medium-coarse sands. Furthermore, the dip-directions of cross-bedded sands revealed in box-cores mainly trend towards the south or southeast, i.e. towards the inlet and not towards the supposed down-drift bypass corridor. As a consequence, sediment transport follows a semi-circular recycling pattern due to the interaction between tidal currents and high waves generated by strong northwesterly winds and storms. The inlet sediment bypassing model postulated in earlier publications is therefore refuted. On the other hand, the lower shoreface off Spiekeroog island is characterized by extensive shoreface-connected sand ridges striking in a NW-SE direction. Thus, the grain-size pattern shows trough-ward coarsening due to the presence of exposed palimpsest lag deposits such as gravels in the troughs. By comparing the spatial sediment distribution patterns of repeated surveys between 1989 and 2005, the most remarkable feature is that the coarse sediments (coarse sands to gravels) normally occupying the outer trough (around 15 m water depth) expanded onto the lower ridge flanks. This phenomenon is hard to be explained with tidal current action alone since the tidal current speeds in this environment are insufficient to transport such coarse material. Accordingly, wave action or wave-amplified tidal currents are the only mechanism capable of explaining this coarse sediment expansion. In order to illustrate this, the oscillatory threshold velocities of the 'effective' wave bases for different wave periods and heights characteristic for the local seasonal wave climates were calculated.
    Dissertation
      545  329