Channel bifurcation in braided rivers: Equilibrium configurations and stability

Pittaluga, M. Bolla; Repetto, Rodolfo; Tubino, Marco

doi:10.1029/2001wr001112

Cited by 168 publications

(472 citation statements)

References 12 publications

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“…Dune bedforms through the reach mostly scale, as expected, with the flow depth, with dunes up to 4·0 m high being present through the central scour, which is up to 22 m deep. These dunes reduce in amplitude through the diffluence but remain roughly scaled with the flow depth, with maximum heights approaching 2·2 m in a flow depth of ~7·5 m. There also appears to be no inlet step in bed height in either of the diffluent channels, as has been reported in some gravel-bed diffluences (Bolla Pittaluga et al, 2003;Zolezzi et al, 2006). the bifurcation.…”

Section: Bed Morphologymentioning

confidence: 56%

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

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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: Bed Morphologymentioning

confidence: 56%

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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“…A major role is played by channel bar bifurcations that distribute discharge and sediment through the braided channel network (Bolla Pittaluga et al, 2003). Commonly, bifurcations are unstable, meaning that the distribution changes over time .…”

Section: Bar and Channel Dynamics In Braided Riversmentioning

confidence: 99%

Network response to disturbances in large sand-bed braided rivers

2016

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Abstract. The reach-scale effects of human-induced disturbances on the channel network in large braided rivers are a challenge to understand and to predict. In this study, we simulated different types of disturbances in a large braided river to get insight into the propagation of disturbances through a braided channel network. The results showed that the disturbances initiate an instability that propagates in the downstream direction by means of alteration of water and sediment division at bifurcations. These adjustments of the bifurcations change the migration and shape of bars, with a feedback to the upstream bifurcation and alteration of the approaching flow to the downstream bifurcation. This way, the morphological effect of a disturbance amplifies in the downstream direction. Thus, the interplay of bifurcation instability and asymmetrical reshaping of bars was found to be essential for propagation of the effects of a disturbance. The study also demonstrated that the large-scale bar statistics are hardly affected.

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“…Two distributaries with identical downstream boundary conditions and a given upstream Shields stress (Q) distribute water and sediment asymmetrically because this is a stable equilibrium configuration [Wang et al, 1995;Slingerland and Smith, 1998;Bolla Pittaluga et al, 2003;Miori et al, 2006;Zolezzi et al, 2006;Bertoldi and Tubino, 2007;Edmonds and Slingerland, 2008;Kleinhans et al, 2008]. For a given Q, upstream channel roughness, and channel aspect ratio, there exists only one asymmetric discharge ratio (Q r ) for which the downstream bifurcate channels are stable to small perturbations.…”

Section: Motivationmentioning

confidence: 99%

Response of river‐dominated delta channel networks to permanent changes in river discharge

Edmonds

Slingerland

Best

et al. 2010

Geophysical Research Letters

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[1] Using numerical experiments, we investigate how river-dominated delta channel networks are likely to respond to changes in river discharge predicted to occur over the next century as a result of environmental change. Our results show for a change in discharge up to 60% of the initial value, a decrease results in distributary abandonment in the delta, whereas an increase does not significantly affect the network. However, an increase in discharge beyond a threshold of 60% results in channel creation and an increase in the density of the distributary network. This behavior is predicted by an analysis of an individual bifurcation subject to asymmetric water surface slopes in the bifurcate arms. Given that discharge in most river basins will change by less than 50% in the next century, our results suggest that deltas in areas of increased drought will be more likely to experience significant rearrangement of the delta channel network. Motivation[2] An immediate impact of climate change and human modifications to river catchments is that the long-term average discharge of most rivers will change appreciably over the next century [Nohara et al., 2006;Palmer et al., 2008]. On rivers that terminate in marine or lacustrine basins, this hydrological change also will impact their deltas, and yet no framework exists for predicting the adjustments deltas may undergo as discharge changes. Relative sea-level rise is already threatening the world's deltas [Blum and Roberts, 2009;Syvitski et al., 2009], and that problem could be further compounded if permanent changes in discharge also dramatically alter delta landscapes, which provide wetlands, biodiversity,, and homes to a significant part of the world's population [Coleman, 1988;Day et al., 2007]. Studies to date have focused on identifying which deltas are at risk [Day et al., 1995;Ericson et al., 2006] and how they might respond to perturbations such as sea-level rise [Jerolmack, 2009]. But, how deltaic distributary networks will respond to changes in river discharge remains unknown.[3] As the long-term average river discharge (Q) changes, the most dramatic response of a deltaic channel network, apart from a full avulsion caused by delta-lobe switching [Coleman, 1988], is abandonment or initiation of distributary channels. This scenario could be expected because the number of bifurcations in a distributary network correlates positively with the input Q and inversely with the power in the marine environment [Syvitski and Saito, 2007]. However, it is unclear whether an individual delta's response to changes in Q would follow the same trend between Q and channel number observed from the Syvitski and Saito delta compilation.[4] Past work has shown that the splitting of discharges at channel bifurcations is subject to fairly stringent stability conditions. Two distributaries with identical downstream boundary conditions and a given upstream Shields stress (Q) distribute water and sediment asymmetrically because this is a stable equilibrium configuration [Wang et al., 1995;S...

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Channel bifurcation in braided rivers: Equilibrium configurations and stability

Cited by 168 publications

References 12 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

Network response to disturbances in large sand-bed braided rivers

Response of river‐dominated delta channel networks to permanent changes in river discharge

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