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Flow fields, bed shear stresses, and suspended bed sediment dynamics in bifurcations of a large river

Authors

  • R. N. Szupiany,

    Corresponding author
    1. Faculty of Engineering and Water Sciences, Littoral National University,Santa Fe,Argentina
      Corresponding author: R. N. Szupiany, Faculty of Engineering and Water Sciences, Littoral National University, Paraje El Pozo, RN 168, km 472, Santa Fe, CP 3000, Argentina. (rszupian@fich1.unl.edu.ar)
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  • M. L. Amsler,

    1. Faculty of Engineering and Water Sciences, Littoral National University,Santa Fe,Argentina
    2. Instituto Nacional de Limnología, National Council of Scientific and Technical Research,Santa Fe,Argentina
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  • J. Hernandez,

    1. Ven Te Chow Hydrosystems Laboratory, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign,Urbana, Illinois,USA
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  • D. R. Parsons,

    1. School of Geography, Faculty of Science, University of Hull,Hull,UK
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  • J. L. Best,

    1. Ven Te Chow Hydrosystems Laboratory, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign,Urbana, Illinois,USA
    2. Department of Geology, Geography and Geographic Information Science and Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign,Urbana, Illinois,USA
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  • E. Fornari,

    1. Faculty of Engineering and Water Sciences, Littoral National University,Santa Fe,Argentina
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  • A. Trento

    1. Faculty of Engineering and Water Sciences, Littoral National University,Santa Fe,Argentina
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Corresponding author: R. N. Szupiany, Faculty of Engineering and Water Sciences, Littoral National University, Paraje El Pozo, RN 168, km 472, Santa Fe, CP 3000, Argentina. (rszupian@fich1.unl.edu.ar)

Abstract

[1] Channel bifurcations associated with bars and islands are important nodes in braided rivers and may control flow partitioning and thus affect downstream confluences, as well as the formation and dynamics of bars. However, the morphodynamic processes associated with bar formation are poorly understood, and previous studies have largely concerned laboratory experiments, small natural streams, or numerical analyses with large Froude numbers, high slopes, and low Shields stresses. In these cases, the morphologic changes at bifurcations are relatively rapid, with predominant bed load transport and the suspended load playing a minor role. In this paper, the evolution of the flow structure and suspended bed sediment transport along four expansion-diffluence units in the Rio Paraná, Argentina, are described. The Rio Paraná is a large multichannel river with a bed composed of medium and fine sands and possesses low Froude numbers and high suspended bed material transport. Primary and secondary flow velocity components were measured with an acoustic Doppler current profiler (ADCP) along the expansion-diffluence units, and the backscatter signal of the ADCP was calibrated to allow simultaneous measurements of suspended bed sediment concentrations. The interactions between these variables show that the cores of primary flow velocity and suspended bed sediment concentration do not necessarily follow the thalweg at the bifurcation and that inertial effects on the suspended bed sediment may influence the morphodynamics of bar formation. It is suggested that changes in flow stage, as well as the presence of vegetation, may further increase the deposition of suspended bed sediment at the bar head. This study suggests that the ratio of suspended bed material to bed load is an important factor controlling the morphodynamics of bifurcations in large sand bed braided rivers.

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