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Hydrodynamics and contaminant transport on a degraded bed at a 90-degree channel confluence

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A Discussion to this article was published on 14 July 2018

Abstract

Channel confluences at which two channels merge have an important effect on momentum exchange and contaminant diffusion in both natural rivers and artificial canals. In this study, a three-dimensional numerical model, which is based on the Reynolds Averaged Navier–Stokes equations and Reynolds Stress Turbulence model, is applied to simulate and compare flow patterns and contaminant transport processes for different bed morphologies. The results clearly show that the distribution of contaminant concentrations is mainly controlled by the shear layer and two counter-rotating helical cells, which in turn are affected by the discharge ratio and the bed morphology. As the discharge ratio increases, the shear flow moves to the outer bank and the counter-clockwise tributary helical cell caused by flow deflection is enlarged, leading the mixing happens near the outer bank and the mixing layer distorted. The bed morphology can induce shrinkage of the separation zone and increase of the clockwise main channel helical cell, which is initiated by the interaction between the tributary helical cell and the main channel flow and strengthened by the deep scour hole. The bed morphology can also affect the distortion direction of the mixing layer. Both a large discharge ratio and the bed morphology could lead to an increase in mixing intensity.

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Acknowledgements

This research was funded by National Science Foundation of China (Grand Nos. 51239003, 51509073 and 51779080), the Research Innovation Program for Graduate Students of Jiangsu Province (Grand No. B1504703), and the Program of Introducing Talents of Discipline to Universities (111 Project, Grand No. B17015). The opinions and conclusions described in this paper are solely those of the authors and do not necessarily reflect the opinions or policies of the sponsors. Thanks are also extended to Huaihe River Basin Water Resources Protection Bureau for their support during the experiments. The authors are grateful to the anonymous reviewers for comments that helped improve the paper.

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Authors and Affiliations

  1. State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing, 210098, China

    Hongwu Tang & Saiyu Yuan

  2. State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing, 210098, China

    Huiming Zhang

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  1. Hongwu Tang
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Correspondence to Hongwu Tang.

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Tang, H., Zhang, H. & Yuan, S. Hydrodynamics and contaminant transport on a degraded bed at a 90-degree channel confluence. Environ Fluid Mech 18, 443–463 (2018). https://doi.org/10.1007/s10652-017-9562-8

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