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Analysis of coherent flow structures over alluvial dunes revealed by multi-beam echo-sounder acoustic backscatter
Simmons, S.M.; Parsons, D.R.; Best, J.L.; Orfeo, O.; Czuba, J.A.; Boldt, J.A.; Oberg, K.A. (2013). Analysis of coherent flow structures over alluvial dunes revealed by multi-beam echo-sounder acoustic backscatter, in: Van Lancker, V. et al. (Ed.) MARID 2013: Fourth International Conference on Marine and River Dune Dynamics. Bruges, Belgium, 15-17 April 2013. VLIZ Special Publication, 65: pp. 249-253
In: Van Lancker, V.; Garlan, T. (Ed.) (2013). MARID 2013: Fourth International Conference on Marine and River Dune Dynamics. Bruges, Belgium, 15-17 April 2013. VLIZ Special Publication, 65. Royal Belgian Institute of Natural Sciences/SHOM/Flanders Marine Institute (VLIZ): Oostende. ISBN 978-2-11-128352-7. 338 pp., more
In: VLIZ Special Publication. Vlaams Instituut voor de Zee (VLIZ): Oostende. ISSN 1377-0950, more

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Keyword
    Fresh water

Authors  Top 
  • Simmons, S.M.
  • Parsons, D.R.
  • Best, J.L.
  • Orfeo, O.
  • Czuba, J.A.
  • Boldt, J.A.
  • Oberg, K.A.

Abstract
    Large-scale coherent flow structures, or macroturbulence, produced by alluvial sand dunes are reasoned to dominate the flow field and result in significant transport of suspended bed sediment. Macroturbulence, and its interaction with the free flow surface, is also thought to influence the creation and maintenance of the dune bed morphology. Recent physical and numerical modelling has demonstrated the structure and origin of such turbulence, and field data obtained along vertical profiles using acoustic Doppler current profilers have also recently enabled a quantification of such turbulence from within natural channels. We have recently developed a novel method, based upon acoustic backscatter from multibeam echo sounding systems, which allows for the simultaneous quantification of suspended sediment dynamics and estimates of flow velocity (see Simmons et al.,2010; Best et al., 2010). This paper presents a full application of this new technique to data collected over dune bedforms in two large rivers: the Rio Paraná and the Mississippi River. An analysis of the mean velocity components and turbulence intensity across the flow field and the quadrant analysis of the flow structures, together with a description of the temporal length cales revealed by wavelet analysis, are presented. These field results are compared with recent numerical modelling of coherent macroturbulence over dune-covered beds, allowing verification of our conceptual models of these key features of many river flows.

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