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Earth System Dynamics An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/esd-2018-78
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/esd-2018-78
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 03 Dec 2018

Research article | 03 Dec 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Earth System Dynamics (ESD).

Maximum power of saline and fresh water mixing in estuaries

Zhilin Zhang and Hubert Savenije Zhilin Zhang and Hubert Savenije
  • Department of Water Management, Delft University of Technology, Delft, the Netherlands

Abstract. Natural systems evolve towards a state of maximum power (Kleidon, 2016), leading to higher levels of entropy production by different mechanisms, including the gravitational circulation in alluvial estuaries. Gravitational circulation is driven by the potential energy of the fresh water. Due to the density difference between seawater and riverwater, the water level on the river side is higher. The hydrostatic forces on both sides are equal, but have different working lines. This triggers an (accelerating) angular moment, providing rotational kinetic energy into the system, part of which drives mixing by gravitational circulation mixing; the remainder is transferred into dissipated energy by friction while mixing. With a constant discharge over a tidal cycle, the density-driven gravitational circulation in the estuarine system performs work at maximum power, lifting up saline water and bringing down fresh water against gravity. The rotational flow causes the spread of salinity, which is mathematically represented by the dispersion coefficient. Accordingly, a new equation for the dispersion coefficient due to the density-driven mechanism has been derived. Together with the steady state advection-dispersion equation, this resulted in a new analytical model for gravitational salinity intrusion. The simulated longitudinal salinity profiles have been confronted with observations in a myriad of estuaries worldwide. It shows that the performance is promising in eighteen out of twenty-three estuaries, with relatively large convergence length. Finally, a predictive equation is presented for the dispersion coefficient at the boundary. Overall, the maximum power concept has provided an alternative for describing the dispersion coefficient due to gravitational circulation in alluvial estuaries.

Zhilin Zhang and Hubert Savenije
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Status: open (until 18 Jan 2019)
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Zhilin Zhang and Hubert Savenije
Zhilin Zhang and Hubert Savenije
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