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The Effect of Small Density Differences at River Confluences

1
Faculty of Civil Engineering and Geosciences, Delft University of Technology, 2628CN Delft, The Netherlands
2
Deltares, 2629HV Delft, The Netherlands
*
Author to whom correspondence should be addressed.
Current address: Laboratory of Hydraulics, Hydrology and Glaciology, ETH Zürich.
Water 2020, 12(11), 3084; https://doi.org/10.3390/w12113084
Received: 12 October 2020 / Revised: 28 October 2020 / Accepted: 30 October 2020 / Published: 3 November 2020
(This article belongs to the Section Hydraulics and Hydrodynamics)
Remarkable 3D flow structures occur at river confluences with small density differences due to differences in sediment concentration or temperature. We explain these by comparing numerical simulations for an idealized confluence with aerial photographs of several river confluences where color differences express the pattern of density differences at the surface. We analyzed numerical simulations of the Rio Negro–Solimões confluence near Manaus, Brazil, in more detail. The numerical model of the idealized confluence showed that the dense water flowed under the light water and the light water over the dense water in a spiraling motion, distorting the interface between the two waters. The horizontal part of this interface moves upwards in downstream direction. Constraining of the spiraling motion in a narrow river downstream of the confluence can cause local up- and downwelling near the banks. A mixing layer can develop when the flow velocities of the two tributaries differ, but strong spiraling motion due to the density differences can suppress this development. The aerial photographs and all numerical simulations showed similar density patterns at the water surface. Even small density differences can have a significant impact and hence need to be considered when analyzing and modeling 3D flow at confluences. View Full-Text
Keywords: confluence; density differences; temperature differences; sediment concentration; flow patterns; coherent structures; hydrodynamic modeling; mixing layer confluence; density differences; temperature differences; sediment concentration; flow patterns; coherent structures; hydrodynamic modeling; mixing layer
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MDPI and ACS Style

van Rooijen, E.; Mosselman, E.; Sloff, K.; Uijttewaal, W. The Effect of Small Density Differences at River Confluences. Water 2020, 12, 3084. https://doi.org/10.3390/w12113084

AMA Style

van Rooijen E, Mosselman E, Sloff K, Uijttewaal W. The Effect of Small Density Differences at River Confluences. Water. 2020; 12(11):3084. https://doi.org/10.3390/w12113084

Chicago/Turabian Style

van Rooijen, Erik; Mosselman, Erik; Sloff, Kees; Uijttewaal, Wim. 2020. "The Effect of Small Density Differences at River Confluences" Water 12, no. 11: 3084. https://doi.org/10.3390/w12113084

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