Mechanisms Driving the Time-Dependent Salt Flux in a Partially Stratified Estuary*

Lerczak, James A.; Geyer, W. Rockwell; Chant, Robert J.

doi:10.1175/jpo2959.1

Cited by 181 publications

(268 citation statements)

References 35 publications

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“…During the neap-tide releases, the vertical extent of the dye was significantly less than the overall water depth, which reduces the effective dispersion rate as roughly the 4th power of the fractional depth of the dye (assuming linear shear). If the initial distribution of dye extended through the entire water column, the dispersion rate of dye would be the same as the overall estuarine dispersion rate, which reaches the extraordinary rate of more than 2000 m 2 /s during neap tides according to Lerczak et al [2006]. Such large dispersion rates require very weak levels of vertical mixing across the pycnocline, consistent with these observations of K z = 4 Â 10 À5 m 2 /s in the pycnocline during the neaps.…”

Section: Discussionsupporting

confidence: 68%

“…The releases occurred during a variety of different tidal phases, as indicated in Table 1. River discharge was about 500 m 3 /s, which is close to the annual average, although there were discharge events before the first dye release and between the second and third releases, producing stronger horizontal and vertical salinity gradients than average [see Lerczak et al, 2006]. [8] Fluoroscein dye was selected for this study, because it has similar detection limits to Rhodamine, but it is approximately 5 times less expensive, allowing a much larger signal for a given cost.…”

Section: Methodsmentioning

confidence: 99%

“…[53] Lerczak et al [2006] performed a detailed analysis of the salt flux for the Hudson estuary based on the moored array deployed during the dye study. They estimated the effective longitudinal dispersion rate for the estuary based on the global salt balance equation (3), averaging over tides and low-frequency oscillations.…”

Section: Comparison With Estimates Of Overall Estuarine Dispersionmentioning

confidence: 99%

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Tidal and spring‐neap variations in horizontal dispersion in a partially mixed estuary

2008

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[1] A sequence of dye releases in the Hudson River estuary provide a quantitative assessment of horizontal dispersion in a partially mixed estuary. Dye was released in the bottom boundary layer on 4 separate occasions, with varying tidal phase and spring-neap conditions. The three-dimensional distribution of dye was monitored by two vessels with in situ, profiling fluorometers. The three-dimensional spreading of the dye was estimated by calculating the time derivative of the second moment of the dye in the along-estuary, cross-estuary and vertical directions. The average along-estuary dispersion rate was about 100 m 2 /s, but maximum rates up to 700 m 2 /s occurred during ebb tides, and minimum rates occurred during flood. Vertical shear dispersion was the principal mechanism during neap tides, but transverse shear dispersion became more important during springs. Suppression of mixing across the pycnocline limited the vertical extent of the patch in all but the maximum spring-tide conditions, with vertical diffusivities in the pycnocline estimated at 4 Â 10 À5 m 2 /s during neaps. The limited vertical extent of the dye patch limited the dispersion of the dye relative to the overall estuarine dispersion rate, which was an order of magnitude greater than that of the dye. This study indicates that the effective dispersion of waterborne material in an estuary depends sensitively on its vertical distribution as well as the phase of the spring-neap cycle.

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Section: Discussionsupporting

confidence: 68%

Section: Methodsmentioning

confidence: 99%

Section: Comparison With Estimates Of Overall Estuarine Dispersionmentioning

confidence: 99%

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Tidal and spring‐neap variations in horizontal dispersion in a partially mixed estuary

2008

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“…We decomposed the flux following the method described by Lerczak et al [2006]. This routine opts for simplicity by grouping into only three terms: a sectionally and tidally averaged term, a sectionally varying and tidally averaged term, and a remainder term, which is sectionally and tidally varying:…”

Section: Sigma Coordinates and Decompositionmentioning

confidence: 99%

“…Full details of the derivation can be found in Lerczak et al [2006] and MacCready and Banas [2011]. This mathematical procedure makes no assumptions about estuary or tidal-river properties.…”

Section: Sigma Coordinates and Decompositionmentioning

confidence: 99%

Sediment dynamics in the lowerMekongRiver: Transition from tidal river to estuary

et al. 2015

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A better understanding of flow and sediment dynamics in the lowermost portions of large‐tropical rivers is essential to constraining estimates of worldwide sediment delivery to the ocean. Flow velocity, salinity, and suspended‐sediment concentration were measured for 25 h at three cross sections in the tidal Song Hau distributary of the Mekong River, Vietnam. Two campaigns took place during comparatively high‐seasonal and low‐seasonal discharge, and estuarine conditions varied dramatically between them. The system transitioned from a tidal river with ephemeral presence of a salt wedge during high flow to a partially mixed estuary during low flow. The changing freshwater input, sediment sources, and estuarine characteristics resulted in seaward sediment export during high flow and landward import during low flow. The Dinh An channel of the Song Hau distributary exported sediment to the coast at a rate of about 1 t s−1 during high flow and imported sediment in a spatially varying manner at approximately 0.3 t s−1 during low flow. Scaling these values results in a yearly Mekong sediment discharge estimate about 65% smaller than a generally accepted estimate of 110 Mt yr−1, although the limited temporal and spatial nature of this study implies a relatively high degree of uncertainty for the new estimate. Fluvial advection of sediment was primarily responsible for the high‐flow sediment export. Exchange‐flow and tidal processes, including local resuspension, were principally responsible for the low‐flow import. The resulting bed‐sediment grain size was coarser and more variable during high flow and finer during low, and the residual flow patterns support the maintenance of mid‐channel islands.

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An observational study of salt fluxes in Delaware Bay

Aristizábal

Chant

2015

JGR Oceans

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An observational study was conducted in Delaware Bay during the summer of 2011 aiming to quantify the different mechanisms driving the salt flux in this system. Seven moorings, equipped with bottom-mounted ADCPs and CT sensors at difference depths, were deployed across a section of the estuary. The total area-averaged and tidal-averaged salt flux was decomposed in three different contributions: the advective salt flux that represents the flux caused by river input and meteorological-induced flows, the steady shear dispersion that is the salt flux driven by the estuarine exchange flow, and the tidal oscillatory salt flux that is induced by the tidal currents. The advective salt flux dominated over the steady shear dispersion and tidal oscillatory salt flux, because it was driven mainly by changes in sea surface height associated with wind-driven setup and setdown. The steady shear dispersion was always positive and presented a spring/neap variability that was consistent with a two-layer exchange flow. On the other hand, the tidal oscillatory salt flux fluctuated between positive and negative values, but increased around a strong neap tide and decreased on the following spring tide. This variability is contrary to previous parameterizations, whereby the tidal salt flux is proportional to the amplitude of the tidal currents. The observational estimate was compared to a parameterization that relates tidal salt flux as proportional to tidal current amplitude and stratification. The observational estimate agreed with this new parameterization when the river discharge was relatively constant.

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Mechanisms Driving the Time-Dependent Salt Flux in a Partially Stratified Estuary*

Cited by 181 publications

References 35 publications

Tidal and spring‐neap variations in horizontal dispersion in a partially mixed estuary

Tidal and spring‐neap variations in horizontal dispersion in a partially mixed estuary

Sediment dynamics in the lowerMekongRiver: Transition from tidal river to estuary

An observational study of salt fluxes in Delaware Bay

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