期刊
JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS
卷 119, 期 4, 页码 2386-2402出版社
AMER GEOPHYSICAL UNION
DOI: 10.1002/2013JC009488
关键词
mixing rate; river confluence; density contrast; meandering channel; mixing layer distortion
类别
资金
- Spanish Ministry of the Environment
- Spanish Ministry of Science and Innovation [CGL2008-06101/BOS]
Simulations of tracer experiments conducted with a three-dimensional primitive-equation hydrodynamic and transport model are used to understand the processes controlling the rate of mixing between two rivers (Ebro and Segre), with distinct physical and chemical properties, at their confluence, upstream of a meandering reservoir (Ribarroja reservoir). Mixing rates downstream of the confluence are subject to hourly scale oscillations, driven partly by changes in inflow densities and also as a result of turbulent eddies that develop within the shear layer between the confluent rivers and near a dead zone located downstream of the confluence. Even though density contrasts are lowat most O(10(-1)) kg m(-3) difference among sourcesand almost negligible from a dynamic point of viewcompared with inertial forcesthey are important for mixing. Mixing rates between the confluent streams under weakly buoyant conditions can be of up to 40% larger than those occurring under neutrally buoyant conditions. The buoyancy effects on mixing rates are interpreted as the result of changes in the contact area available for mixing (distortion of the mixing layer). For strong density contrasts, though, when the contact area between the streams becomes nearly horizontal, larger density differences between streams will lead to weaker mixing rates, as a result of the stabilizing effect of vertical density gradients. Key Points Mixing rates in river confluences are sensitive to weak river-density contrasts Mixing rates increase up to 40% in response to density contrasts of O(0.1) kg m(-3) Channel planform and density contrasts control the area available for mixing
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