Discussion of “Tang, H., Zhang, H., &amp; Yuan, S. (2018). Hydrodynamics and contaminant transport on a degraded bed at a 90-degree channel confluence. Environmental Fluid Mechanics, 18(2), 443–463”

Pouchoulin, Sébastien; Ramos, Pedro Cunha; Mignot, Emmanuel; Schindfessel, Laurent; Mulder, Tom De; Rivière, Nicolas

doi:10.1007/s10652-018-9612-x

Cited by 4 publications

(1 citation statement)

References 8 publications

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“…Recent field experiments by Sukhodolov and Sukhodolova (2019) have used theory of flow through bends to predict documented patterns of helical motion at confluences. On the other hand, upwelling motion (Lane et al, 2008) occurs when one confluent flow rides over the other (Pouchoulin et al, 2018; Shakibainia et al, 2010), possibly over the full width of the downstream channel. The factors that initiate and enhance both helical and upwelling motions are still not fully understood.…”

Section: Introductionmentioning

confidence: 99%

Predicting Transverse Mixing Efficiency Downstream of a River Confluence

Pouchoulin

Coz

Mignot

et al. 2020

Water Resources Research

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Predicting mixing processes, especially transverse mixing, downstream of river confluences, is necessary for assessing and modeling the fate of pollutants transported in river networks, but it is still challenging. Typically, there is a lack of transverse mixing solutions implemented in 1-D hydrodynamical models widely used in river engineering applications. To investigate the mixing processes developing downstream of a medium-sized river confluence, three high-resolution in situ surveys are conducted at the Rhône-Saône confluence in France, based on geolocated specific conductivity and hydroacoustic measurements. Contrasting mixing situations are observed depending on hydrological conditions. In some cases, the two flows mix slowly due to turbulent shear at their vertical interface. This can be modeled by an analytical solution of the advection-diffusion equation. In other cases, the waters from one of the two tributaries move under the waters of the other tributary. The induced local circulation enhances transverse mixing but not vertical mixing and the flow remains stratified vertically, which may be missed when surface or satellite images are analyzed qualitatively. Stratification may be predicted by comparing the time scales for shear and density-driven adjustment. Shear-dominated transverse mixing of depth-averaged concentrations can be predicted analytically and implemented in 1-D hydrodynamical models. However, the initiation of apparently rapid transverse mixing due to density-driven circulation remains to be better understood and quantified. Plain Language Summary Predicting how waters mix downstream of river confluences is necessary for assessing and modeling the fate of pollutants transported in river networks, but it is still challenging. Typically, there is a lack of transverse mixing solutions implemented in models widely used in river engineering applications. To investigate the mixing processes developing downstream of a medium-sized river confluence, three high-resolution in situ surveys are conducted at the Rhône-Saône confluence in France. Contrasting slow or rapid mixing situations are observed depending on hydrological conditions. The transverse mixing of depth-averaged concentrations can be predicted analytically and implemented in 1-D hydrodynamical models. However, the initiation of rapid transverse mixing due to difference in fluid density remains to be better understood and quantified.

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Section: Introductionmentioning

confidence: 99%

Predicting Transverse Mixing Efficiency Downstream of a River Confluence

Pouchoulin

Coz

Mignot

et al. 2020

Water Resources Research

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

Ramos

Schindfessel

Pêgo

et al. 2019

Water Science and Engineering

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Flat vs. curved rigid-lid LES computations of an open-channel confluence

Ramos

Schindfessel

Pêgo

et al. 2019

Journal of Hydroinformatics

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This paper describes the application of four Large Eddy Simulations (LES) to an open-channel confluence flow, making use of a frictionless rigid-lid to treat the free-surface. Three simulations are conducted with a flat rigid-lid, at different elevations. A fourth simulation is carried out with a curved rigid-lid which is a closer approximation to the real free-surface of the flow. The curved rigid-lid is obtained from the time-averaged pressure field on the flat rigid-lid from one of the initial three simulations. The aim is to investigate the limitations of the free-surface treatment by means of a rigid-lid in the simulation of an asymmetric confluence, showing the differences that both approaches produce in terms of mean flow, secondary flow and turbulence. After validation with experimental data, the predictions are used to understand the differences between adopting a flat and a curved rigid-lid onto the confluence hydrodynamics. For the present flow case, although it was characterized by a moderately low downstream Froude number (Fr ≈ 0.37), it was found that an oversimplification of the numerical treatment of the free-surface leads to a decreased accuracy of the predictions of the secondary flow and turbulent kinetic energy.

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Discussion of “Tang, H., Zhang, H., & Yuan, S. (2018). Hydrodynamics and contaminant transport on a degraded bed at a 90-degree channel confluence. Environmental Fluid Mechanics, 18(2), 443–463”

Cited by 4 publications

References 8 publications

Predicting Transverse Mixing Efficiency Downstream of a River Confluence

Predicting Transverse Mixing Efficiency Downstream of a River Confluence

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

Flat vs. curved rigid-lid LES computations of an open-channel confluence

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