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

机译：一条大河分叉处的流场，床剪应力和悬浮床沉积物动力学

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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 Parana, Argentina, are described. The Rio Parana 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.
机译：与条形和岛形相关的河道分叉是辫状河中的重要节点，并可能控制流量分配，从而影响下游汇流以及条形和动力。但是，与钢筋形成相关的形态动力学过程了解甚少，并且以前的研究主要涉及实验室实验，小的自然流或具有大弗洛德数，高斜率和低Shields应力的数值分析。在这些情况下，分叉处的形态变化相对较快，主要是床荷载运输，而悬挂荷载作用较小。本文描述了阿根廷里约帕拉纳河沿四个扩展-扩散单元的流动结构演变和悬浮床沉积物的运移。里约帕拉纳河是一条大型多渠道河流，河床由中细砂组成，弗洛德数低，悬浮床物料运输量高。沿扩展-扩散单元使用声学多普勒电流剖面仪（ADCP）测量主要和次要流速分量，并校准ADCP的反向散射信号以允许同时测量悬浮床沉积物浓度。这些变量之间的相互作用表明，主流速和悬浮床沉积物浓度的核心不一定在分支处跟随thalweg，并且对悬浮床沉积物的惯性影响可能会影响棒形成的形态动力学。建议在水流阶段的变化以及植被的存在可能会进一步增加杆头处悬浮床沉积物的沉积。这项研究表明，悬浮床材料与床荷载的比率是控制大型沙床辫状河分叉形态动力学的重要因素。

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  • 来源
    《Water resources research》 |2012年第11期|W11515.1-W11515.20|共20页
  • 作者

    R. N. Szupiany; M. L. Amsler; J. Hernandez; D. R. Parsons; J. L. Best; E. Fornari; A. Trento;

  • 作者单位

    Faculty of Engineering and Water Sciences, Littoral National University, Paraje El Pozo, RN 168, km 472, Santa Fe, CP 3000, Argentina;

    Faculty of Engineering and Water Sciences, Littoral National University, Santa Fe, Argentina,Instituto Nacional de Limnologia, National Council of Scientific and Technical Research, Santa Fe, Argentina;

    Ven Te Chow Hydrosystems Laboratory, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign,Urbana, Illinois, USA;

    School of Geography, Faculty of Science, University of Hull, Hull,UK;

    Ven Te Chow Hydrosystems Laboratory, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign,Urbana, Illinois, USA,Department of Geology, Geography and Geographic Information Science and Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, USA;

    Faculty of Engineering and Water Sciences, Littoral National University, Santa Fe, Argentina;

    Faculty of Engineering and Water Sciences, Littoral National University, Santa Fe, Argentina;

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