Transport in the Hudson estuary: A modeling study of estuarine circulation and tidal trapping |
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Authors: | Email author" target="_blank">Ferdi?L?HellwegerEmail author Alan?F?Blumberg Peter?Schlosser David?T?Ho Theodore?Caplow Upmanu?Lall Honghai?Li |
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Institution: | 1.Department of Earth and Environmental Engineering,Columbia University,New York;2.HydroQual, Inc,Mahwah;3.Stevens Institute of Technology,Castle Point on Hudson,Hoboken;4.Lamont-Doherty Earth Observatory,Columbia University,Palisades;5.Department of Earth and Environmental Sciences,Columbia University,New York |
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Abstract: | The effects of estuarine circulation and tidal trapping on transport in the Hudson estuary were investigated by a large-scale,
high-resolution numerical model simulation of a tracer release. The modeled and measured longitudinal profiles of surface
tracer concentrations (plumes) differ from the ideal Gaussian shape in two ways: on a large scale the plume is asymmetric
with the downstream end stretching out farther, and small-scale (1–2 km) peaks are present at the upstream and downstream
ends of the plume. A number of diagnostic model simulations (e.g., remove freshwater flow) were performed to understand the
processes responsible for these features. These simulations show that the large-scale asymmetry is related to salinity. The
salt causes an estuarine circulation that decreases vertical mixing (vertical density gradient), increases longitudinal dispersion
(increased vertical and lateral gradients in longitudinal velocities), and increases net downstream velocities in the surface
layer. Since salinity intrusion is confined to the downstream end of the tracer plume, only that part of the plume is effected
by those processes, which leads to the largescale asymmetry. The small-scale peaks are due to tidal trapping. Small embayments
along the estuary trap water and tracer as the plume passes by in the main channel. When the plume in the main channel has
passed, the tracer is released back to the main channel, causing a secondary peak in the longitudinal profile. |
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