Multiple thread flow and channel bifurcation in a braided river: Brahmaputra–Jamuna River, Bangladesh

Richardson, William R.; Thorne, Colin R.

doi:10.1016/s0169-555x(00)00080-5

Cited by 117 publications

(52 citation statements)

References 14 publications

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“…[6] By far the most studied bifurcation type has been within low Q channels, whether by field observation [Davoren and Mosley, 1986;Ashmore et al, 1992;Ashworth et al, 1992;Bridge, 1993;Ashworth, 1996;Richardson and Thorne, 2001;Zolezzi et al, 2006;Frings and Kleinhans, 2008], flume studies [Federici and Paola, 2003;Zanichelli et al, 2004;Bertoldi and Tubino, 2005;Islam et al, 2006;Bertoldi and Tubino, 2007], or by numerical modeling [Repetto et al, 2002;Bolla Pittaluga et al, 2003;Dargahi, 2004;Zanichelli et al, 2004;Hall, 2005;Wu and Yeh, 2005;Kleinhans et al, 2008;Miori et al, 2006].…”

Section: Low Q Bifurcationsmentioning

confidence: 99%

Stability of delta distributary networks and their bifurcations

Edmonds

Slingerland

2008

Water Resources Research

122

150

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[1] Delta distributary networks are created by bifurcating channels that commonly split their discharges unequally. The origin and stability of these asymmetrical fine-grained cohesive bifurcations are investigated here using Delft3D, a morphodynamic flow and sediment transport model. Results are compared to bifurcations on the Mossy delta, Saskatchewan, Canada, that have remained stable for decades. Over a range of channel aspect ratios, friction factors, and Shields numbers, we find three equilibrium functions relating the discharge ratio of the bifurcate arms at equilibrium to the Shields number. One function defines symmetrical configurations (equal partitioning of discharge), while the other two define asymmetrical configurations (unequal partitioning of discharge). Discharge asymmetries and morphologies of Mossy delta bifurcations are consistent with these predictions. Among the equilibrium bifurcations, only the asymmetrical type is stable to perturbations, such as a partial closing of one throat. This possibly explains why asymmetrical bifurcations are more common in nature.

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Section: Low Q Bifurcationsmentioning

confidence: 99%

Stability of delta distributary networks and their bifurcations

Edmonds

Slingerland

2008

Water Resources Research

122

150

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“…There is currently an incomplete understanding of the confluence-diffluence unit, including the transition from confluence to diffluence, and the flow characteristics that are inherited at, and downstream of, these sites (see, e.g., Nicholas and Sambrook Smith, 1999;Richardson and Thorne, 2001). The morphology of the diffluence will control the character of flow in the downstream distributaries, and therefore play a critical role in the movement of sediment through the confluence-diffluence unit, governing the development and maintenance of mid-channel bars that are a central part of this unit in braided rivers.…”

Section: Introductionmentioning

confidence: 99%

“…There is almost no knowledge of how the processes observed at these smaller sites scale to larger, wider, rivers (Yalin, 1992), and this represents a fundamental gap in current understanding of how continental-scale river systems function. Notable exceptions are the studies of Richardson et al (1996), McLelland et al (1999) and Richardson and Thorne (2001), who examined secondary flows at bifurcations and around a braid bar in the Jamuna River, Bangladesh. However, these studies did not concern flow within a connected confluence-diffluence unit, which is the focus of the research presented herein.…”

Section: Introductionmentioning

confidence: 99%

Form roughness and the absence of secondary flow in a large confluence–diffluence, Rio Paraná, Argentina

Parsons

Best

Lane

et al. 2006

Earth Surf Processes Landf

162

133

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Confluence-diffluence units are key elements within many river networks, having a major impact upon the routing of flow and sediment, and hence upon channel change. Although much progress has been made in understanding river confluences, and increasing attention is being paid to bifurcations and the important role of bifurcation asymmetry, most studies have been conducted in laboratory flumes or within small rivers with width:depth (aspect) ratios less than 50. This paper presents results of a field-based study that details the bed morphology and 3D flow structure within a very large confluence-diffluence in the Río Paraná, Argentina, with a width:depth ratio of approximately 200. Flow within the confluence-diffluence is dominated largely by the bed roughness, in the form of sand dunes; coherent, channel-scale, secondary flow cells, that have been identified as important aspects of the flow field within smaller channels, and assumed to be present within large rivers, are generally absent in this reach. This finding has profound implications for flow mixing rates, sediment transport rates and pathways, and thus the interpretation of confluence-diffluence morphology and sedimentology.

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“…These authors documented and quantified the interaction between bed features and planform evolution of a laterally unconstrained channel before bifurcation, and determined an objective criterion to define the conditions for the occurrence of bifurcation. Finally, Richardson & Thorne (2001) have described the flow field in a newly formed bifurcation in the sandy Jamuna River, Bangladesh, showing that flow instability can generate a multithread current and therefore trigger the bifurcation process.…”

Section: Introductionmentioning

confidence: 99%

Morphological Analysis and Prediction of River Bifurcations

2006

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Braiding is a complex and highly dynamic process, the evolution of which is at present hard to predict, even on short time-scales. In order to improve the understanding and modelling of braided rivers, there is a need to gain a better insight into the processes of channel bifurcation, which is widely recognized as being important for the onset of braiding. Bifurcations are crucial components of braided rivers that control the adjustment of braiding intensity, since they largely determine the distribution of flow and sediment discharge along the downstream channels. Natural bifurcations show repetitive features in different types of gravel braided rivers. This paper presents a quantitative description of such features, based on observations performed on several bifurcations at two different field sites, and these features are related to the hydraulic conditions of the upstream incoming flow. The observed imbalance of flow partitioning at the bifurcation, which is also reflected by asymmetry in the width of the downstream anabranches, is found to be related to local bed aggradation in the main channel. This is immediately followed by a sudden step in the main channel profile, while the slope of the downstream anabranches remains almost equal and approximately constant downstream. The flow invariably concentrates towards the external bank of the largest downstream channel, enhancing bank erosion over a distance of several channel widths. The resulting data set allows a first assessment of theoretical predictions based on a recent model of bifurcation equilibrium and stability, which is essentially based on a simple one-dimensional formulation. In spite of its approximate character, the model seems to capture, at least qualitatively, the gross recurring features of these bifurcations.

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Multiple thread flow and channel bifurcation in a braided river: Brahmaputra–Jamuna River, Bangladesh

Cited by 117 publications

References 14 publications

Stability of delta distributary networks and their bifurcations

Stability of delta distributary networks and their bifurcations

Form roughness and the absence of secondary flow in a large confluence–diffluence, Rio Paraná, Argentina

Morphological Analysis and Prediction of River Bifurcations

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