Flow Structure and Transport of Sand‐Grade Suspended Sediment around an Evolving Braid Bar, Jamuna River, Bangladesh

McLelland, Stuart J.; Ashworth, Philip; Best, James L.; Roden, Julie E.; Klaassen, G.J.

doi:10.1002/9781444304213.ch4

Cited by 43 publications

(63 citation statements)

References 21 publications

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“…Thus, a preliminary conclusion is that the principal control on the potential absence of secondary circulation in large rivers, and why there is none in this confluence-diffluence unit, appears to be the extent to which form roughness is present that is capable of transmitting near-bed steering of flow throughout the flow depth. The potential role of bed roughness in negating the production of secondary flows was also invoked by McLelland et al (1999) in their study of flow around a large braid bar. The question thus arises as to why this may not also be the case in smaller rivers, since dune height scales with flow depth irrespective of channel size.…”

Section: Secondary Circulationmentioning

confidence: 99%

“…Two factors may be important. First, the lower width:depth (aspect) ratios in smaller rivers may produce channels that are more likely to develop channel-wide secondary flows (Nezu and Nakagawa, 1993;Yalin, 1992;McLelland et al, 1999). Second, the effects of hysteresis in the response of dunes to changing flow stage may be more significant in larger channels, where the sediment volumes within the bedforms are larger, and hence their migration rates will be smaller.…”

Section: Secondary Circulationmentioning

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%

“…Research investigating the processes of flow at river channel confluences has highlighted the possible importance of secondary flows and their controls on channel geometry, channel dynamics, sediment transport and flow mixing (e.g. Ashmore et al, 1992;Best, 1986Best, , 1987Best, , 1988Best and Reid, 1984;Best and Roy, 1991;Biron et al, 1993Biron et al, , 1996Bradbrook et al, 1998Bradbrook et al, , 2000Bradbrook et al, , 2001Lane et al, 2000;McLelland et al, 1999;Mosley, 1976;Rhoads and Kenworthy, 1998;Rhoads and Sukhodolov, 2001). The classical model of flow at a confluence involves divergence between near-bed and nearsurface flows as a result of the interaction between pressure gradient forcing and bed topographic steering.…”

Section: Introductionmentioning

confidence: 99%

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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

163

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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Section: Secondary Circulationmentioning

confidence: 99%

Section: Secondary Circulationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

163

133

View full text Add to dashboard Cite

show abstract

“…A number of past studies have been carried out, particularly concerning morphological processes in the Jamuna since the late 1960s. These include the academic work of Coleman (1969), Bristow (1987), Richardson et al (1996), Best and Ashworth (1997), Richardson and Thome (2001), Islam et al (1999), McLelland et al (1999), Ashworth et al (2000), and Islam and Chowdhury (2003) and consultancy studies carried out under the Jamuna Bridge Authority and the Flood Action…”

Section: Setting the Scenementioning

confidence: 99%

Morphological Response of the Brahmaputra–Padma–Lower Meghna River System to the Assam Earthquake of 1950

Sarker

Thorne

2006

Braided Rivers

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Sediment rating curves Chapter 6 Conceptual model 174 6.1 Introduction 6.2 Celerity of the disturbance in a riverbed 6.3 Changes in the Independent Variables 6.3.1 Changes in the flow regime 6.3.2 Changes in bed sediment size 6.3.3 Changes in the sediment regime 6.4 Changes in the Dependent Variables 6.4.1 Changes in bed elevation 6.4.2 Changes in width 6.4.3 Changes in braiding intensity 6.4.4 Phase lags in the observed morphological changes 65 Development of the conceptual process-response model.. 201 6.5.1 Background 201 6.5.2Adjustments in the upstream reach of the Jamuna River 202 6.5.3 Downstream reach of the

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Interactions between flow structure and morphodynamic of bars in a channel expansion/contraction, Loire River, France

Claude

Rodrigues

Bustillo

et al. 2014

Water Resources Research

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The study of the relationship between flow structure and morphodynamic of bars in a channel expansion/contraction is essential to better understand the processes that control the evolution of rivers. Thus, multibeam echosoundings and Acoustic Doppler Profiler (ADP) measurements were performed with a high temporal resolution in an expansion/contraction zone of the Loire River (France) occupied by bars. During the monitoring period, the macroforms presented successively an alternate, a lateral and a transverse configuration. Field data were analyzed to study how the primary and secondary velocities, the flow directions, the bed shear stresses, and the bed roughnesses (associated to dunes) evolve as a function of the water discharge and bars configuration. The bars modify the flow structure imposed by the channel width variations. In fact, the bars induce a topographic forcing which enables the separation and reducing of the mixing of two currents formed in the upstream channel expansion. This forcing is enhanced by the turbulence formed by the large dunes superimposed on the bars. Therefore, the bars promote a nonuniform flow in the channel. In turn, in the channel expansion/contraction, the migrating bars' morphodynamics are affected by the downstream channel narrowing which stops their downstream migration and forced the bars in the system. Then the nonuniformity of the flow encourages the lateral migration of the macroforms until they reach a bank and become nonmigrating. Finally, the nonmigrating bars are eroded by the flow deflected during the migration of a new bar in the channel expansion/contraction.

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Flow Structure and Transport of Sand‐Grade Suspended Sediment around an Evolving Braid Bar, Jamuna River, Bangladesh

Cited by 43 publications

References 21 publications

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

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

Morphological Response of the Brahmaputra–Padma–Lower Meghna River System to the Assam Earthquake of 1950

Interactions between flow structure and morphodynamic of bars in a channel expansion/contraction, Loire River, France

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