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Earth Syst. Dynam., 9, 241-247, 2018
https://doi.org/10.5194/esd-9-241-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
13 Mar 2018
Thermodynamics of saline and fresh water mixing in estuaries
Zhilin Zhang and Hubert H. G. Savenije Department of Water Management, Delft University of Technology, Delft, the Netherlands
Abstract. The mixing of saline and fresh water is a process of energy dissipation. The freshwater flow that enters an estuary from the river contains potential energy with respect to the saline ocean water. This potential energy is able to perform work. Looking from the ocean to the river, there is a gradual transition from saline to fresh water and an associated rise in the water level in accordance with the increase in potential energy. Alluvial estuaries are systems that are free to adjust dissipation processes to the energy sources that drive them, primarily the kinetic energy of the tide and the potential energy of the river flow and to a minor extent the energy in wind and waves. Mixing is the process that dissipates the potential energy of the fresh water. The maximum power (MP) concept assumes that this dissipation takes place at maximum power, whereby the different mixing mechanisms of the estuary jointly perform the work. In this paper, the power is maximized with respect to the dispersion coefficient that reflects the combined mixing processes. The resulting equation is an additional differential equation that can be solved in combination with the advection–dispersion equation, requiring only two boundary conditions for the salinity and the dispersion. The new equation has been confronted with 52 salinity distributions observed in 23 estuaries in different parts of the world and performs very well.
Citation: Zhang, Z. and Savenije, H. H. G.: Thermodynamics of saline and fresh water mixing in estuaries, Earth Syst. Dynam., 9, 241-247, https://doi.org/10.5194/esd-9-241-2018, 2018.
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Short summary
This paper presents a new equation for the dispersion of salinity in alluvial estuaries based on the maximum power concept. The new equation is physically based and replaces previous empirical equations. It is very useful for application in practice because in contrast to previous methods it no longer requires a calibration parameter, turning the method into a predictive method. The paper presents successful applications in more than 23 estuaries in different parts of the world.
This paper presents a new equation for the dispersion of salinity in alluvial estuaries based on...
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