Influence of bed elevation discordance on flow patterns and head losses in an open-channel confluence

Ramos, Pedro Cunha; Schindfessel, Laurent; Pêgo, João Pedro; Mulder, Tom De

doi:10.1016/j.wse.2019.09.005

Cited by 19 publications

(14 citation statements)

References 30 publications

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“…Note that these findings differ from the enhanced mixing which is usually associated with the presence of bed elevation discordance, as found in studies where a degraded bed in a confluence is schematized to a step in the interface between the (shallower) tributary channel and the main channel (e.g. Bradbrook et al 2001;Ramos et al, 2019b). Downstream of x/W d ≈ 5 up till the end of the present numerical domain at x/W d = 10 (a zone which is not focused on in Tang et al, 2018), the non-uniformity of mixing is found to be somewhat lower for the flat bed case.…”

Section: Discussioncontrasting

confidence: 72%

Numerical study of the flow and passive scalar transport in an open-channel confluence with a flat and a degraded fixed bed

Jin¹,

Ramos²,

Schindfessel³

et al. 2020

River Flow 2020

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Confluences are important junctions in fluvial and artificial networks of open-channels, as they regulate the mixing phenomena of substances transported by the merging flows, as well as the scour and deposition phenomena. This paper aims at contributing to the study of how the bed morphology, such as the presence of a scour hole and a depositional bar, influences the flow and mixing phenomena at a T-shaped open-channel confluence. By means of Large Eddy Simulations (LES) of flow and passive scalar transport, a comparative numerical study is carried out of two fixed bed cases, i.e. a flat one and a degraded one, which were investigated earlier experimentally in the lab and numerically with a RANS based solver by Tang et al. (2018). The spatial focus of the present paper is not exclusively devoted to the Confluence Hydrodynamics Zone, but also extends somewhat further downstream (i.e. up to 10 post-confluence channel widths W d downstream of the upstream confluence corner). For the investigated flow condition with a dominant incoming flow from the upstream main channel, the recirculation zone in the degraded bed case is found to be significantly shorter and less wide or even absent near the bed, yielding differences in the contraction of the main channel flow and in the secondary flow. Nevertheless, the non-uniformity of passive scalar mixing was found to be very similar up to 3.5W d . Further downstream, the flat bed case shows a slightly higher mixing rate, which does not seem to be related to differences in secondary flow patterns, but rather to differences in turbulence levels.

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Section: Discussioncontrasting

confidence: 72%

Numerical study of the flow and passive scalar transport in an open-channel confluence with a flat and a degraded fixed bed

Jin¹,

Ramos²,

Schindfessel³

et al. 2020

River Flow 2020

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“…Discordant river confluences are common in braided rivers with midchannel bars and islands (Szupiany et al., 2009). Bed discordance can enhance the exchange of momentum between two flows (Ramos et al., 2019) and may play a role in the mixing of the left and right branch flows of the Yangtze River. As the maximum water depths of the Yangtze River and the Poyang Lake were similar, this confluence is almost concordant with a negligible effect of bed discordance on the momentum exchange.…”

Section: Resultsmentioning

confidence: 99%

“…Discordant river confluences are common in braided rivers with midchannel bars and islands (Szupiany et al, 2009). Bed discordance can enhance the exchange of momentum between two flows (Ramos et al, 2019) and may play a role in the mixing of the left and right branch flows of the Yangtze River.…”

Section: Bed Morphology Variation Related To Operation Of the Three Gmentioning

confidence: 99%

Hydrodynamics, Sediment Transport and Morphological Features at the Confluence Between the Yangtze River and the Poyang Lake

Yuan

Tang

et al. 2021

Water Resources Research

100

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Confluences are critical nodes in a river network and affect flow, sediment transport, water quality, and ecological patterns. Significant changes in hydrodynamics, bed morphology as well as environmental and ecological features occur at the confluence, where the flows from two tributaries combine and adjust to the postconfluence planform geometry. Confluence of two flows with different momentum and velocity ratios (the ratio of the variable of one channel to that of the other) often results in a downstream shear layer driven by the Kelvin-Helmholtz (KH) instability. It enhances turbulent mixing and exchange of momentum and other matter (e.g., sediment and pollutants;

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“…Também são locais representativos dos aspectos à montante, por possuírem depósitos fluviais e estarem sobrepostos a uma litologia que condiciona determinados processos erosivos. Para Ramos et al (2019) as confluências fluviais regulam o transporte de sedimentos, nutrientes e poluentes por elas serem dissipadoras do fluxo na rede de drenagem.…”

Section: Introductionunclassified

Hidrogeomorfologia em confluência fluvial obtusa, Guarapuava, Paraná

Vestena

Kominecki

2021

Rev. Bras. Geog. Fis.

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Solid and liquid mixtures in river courses intensify in areas of river confluence, conditioned mainly by the angular opening of the junction. Knowledge of hydrosedimentological dynamics in bedrock junctions with different angular openings is essential for understanding morphological adjustment at confluences and for supporting actions for the preservation and conservation of river ecosystems. For this reason, this article presents the results of a hydrogeomorphologic study on a river confluence with an obtuse junction angle (>100º), in a plateau bedrock river, in the Serra Geral Formation. The research evaluated a fluvial segment upstream and downstream of the Pedras River and in the Pombas River tributary, in Guarapuava, Paraná, through observations and measurements of morphological and hydraulic characteristics, width, talweg depth, bed declivity and bankfull flow. Morphological adjustment in obtuse confluences is peculiar in that the fluvial junction angle conditions specific flow, erosion, sediment transport and deposition dynamics, mainly resulting from its association with the geological nature of the river bed and types of land use and management upstream of the confluence.

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Influence of bed elevation discordance on flow patterns and head losses in an open-channel confluence

Cited by 19 publications

References 30 publications

Numerical study of the flow and passive scalar transport in an open-channel confluence with a flat and a degraded fixed bed

Numerical study of the flow and passive scalar transport in an open-channel confluence with a flat and a degraded fixed bed

Hydrodynamics, Sediment Transport and Morphological Features at the Confluence Between the Yangtze River and the Poyang Lake

Hidrogeomorfologia em confluência fluvial obtusa, Guarapuava, Paraná

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