Virginia Institute of Marine Science
Journal of Geophysical Research: Oceans
Stratiﬁcation in estuaries has received much focus due to its importance in estuarine hydrodynamics and material transport. By utilizing a well‐calibrated numerical model, in this work we investigate the changes in stratiﬁcation 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 ﬂow and transverse salinity gradient, is the dominant factor that controls stratiﬁcation. A two‐layer structure of the lateral ﬂow strains the isopycnal transversely, resulting in rapid stratiﬁcation from late ﬂood to early ebb tide. Thus, maximum stratiﬁcation occurs during the early ebb. Then, the stratiﬁcation was suppressed by the vertical mixing and the less stratiﬁed water advected from upstream, even the vertical shear in along‐channel ﬂow 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 ﬂow are profoundly reduced. The impact of lateral straining on stratiﬁcation becomes minor. The enhanced stratiﬁcation results in a sharp decrease in turbulent mixing within the pycnocline. The water movement in the upper layer is in a free‐stream status and the tidal current speed increases signiﬁcantly. The alteration of the vertical current structure enhances the along‐channel tidal straining and stratiﬁcation is most vigorous on late ebb tide.
Zhu, Lei; He, Qing; and Shen, Jian, Response of stratiﬁcation processes to tidal current alteration due to channel narrowing and deepening (2020). Journal of Geophysical Research: Oceans, 125(2), e2019JC015223.
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