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Response of stratiļ¬cation processes to tidal current alteration due to channel narrowing and deepening

Zhu, Lei
; 
He, Qing
; 
Shen, Jian
Abstract
Stratiļ¬cation in estuaries has received much focus due to its importance in estuarine hydrodynamics and material transport. By utilizing a wellā€calibrated numerical model, in this work we investigate the changes in stratiļ¬cation in the deepened and narrowed North Passage of the Changjiang Estuary. Before channel narrowing and deepening, lateral straining, generated by the interaction between vertical shear in lateral ļ¬‚ow and transverse salinity gradient, is the dominant factor that controls stratiļ¬cation. A twoā€layer structure of the lateral ļ¬‚ow strains the isopycnal transversely, resulting in rapid stratiļ¬cation from late ļ¬‚ood to early ebb tide. Thus, maximum stratiļ¬cation occurs during the early ebb. Then, the stratiļ¬cation was suppressed by the vertical mixing and the less stratiļ¬ed water advected from upstream, even the vertical shear in alongā€channel ļ¬‚ow continued to strain the isopycnal. After channel deepening and narrowing, the salinity in the upper water column experienced a sharp vertical gradient during the entire tidal cycle, while the transverse salinity gradient and lateral ļ¬‚ow are profoundly reduced. The impact of lateral straining on stratiļ¬cation becomes minor. The enhanced stratiļ¬cation results in a sharp decrease in turbulent mixing within the pycnocline. The water movement in the upper layer is in a freeā€stream status and the tidal current speed increases signiļ¬cantly. The alteration of the vertical current structure enhances the alongā€channel tidal straining and stratiļ¬cation is most vigorous on late ebb tide.
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2020-02-01
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2019JC015223.pdf
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Physical Sciences Peer-Reviewed Articles
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Virginia Institute of Marine Science
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https://doi.org/10.1029/2019JC015223
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https://scholarworks.wm.edu/handle/internal/17851
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