Impact of Channel Deepening on Tidal and Gravitational Circulation in a Highly Engineered Estuarine Basin
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Deepening of estuarine channels is a common practice to ensure navigation. Here, we investigate whether such deepening impacts physical processes such as the strength of the estuarine exchange flow, the horizontal salinity gradient, and tidal dynamics. We analyze recent and historical hydrodynamic observations in Newark Bay, New Jersey, to assess the effect of channel deepening on tides, circulation, and salinity. The Bay’s navigational channel has undergone significant deepening, from 3 to 10 m in the nineteenth century to ~16 m today. Observations presented here include sea-level data from the nineteenth, twentieth, and twenty-first century, and moored Doppler current data and bottom salinity measurements made over the past 20 years. Results show a doubling of the estuarine exchange flow, a slight increase in salinity and in the horizontal salinity gradient, a decrease in tidal current amplitude, and a spatially variable change in the tidal range. The doubling of the exchange flow is consistent with the Hansen and Rattray scaling provided that the horizontal salinity gradient is unable to fully adjust landward because the dredging is limited to a short reach of the estuary. However, uncertainty in channel depth leaves open the possibility that the exchange flow is also augmented by an increase in the horizontal salinity gradient and/or a reduction in vertical mixing. Nevertheless, results demonstrate that a relatively small (15%) increase in depth appears to have doubled the exchange flow. We believe that this result is relevant to other systems where dredging is limited to a short reach of an estuary.
KeywordsEstuarine exchange flow Channel deepening Estuarine salt intrusion
RJC acknowledges support from the Hudson River Foundation (HRF008/07A) and from a National Science Foundation Coastal SEES grant (1325258). CKS acknowledges support from the Hudson River Foundation (HRF008/07A) and the National Science Foundation (OCE-1325102). Stefan Talke acknowledges the U.S. Army Corps of Engineers (Award W1927N-14-2-0015) and the US National Science Foundation (Career Award 1455350). We thank Chip Haldeman and Elias Hunter for their efforts in the field, and Capt. Ken Roma for his efforts behind the helm. The authors gratefully thank two anonymous reviewers whose thoughtful comment and constructive criticisms of earlier drafts greatly improved this paper.
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