Theoretical analysis of conditions in a salt wedge

Rattray, Maurice; Mitsuda, Eugene

doi:10.1016/0302-3524(74)90006-1

Cited by 57 publications

(33 citation statements)

References 5 publications

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“…Results from the vertically averaged model are then used as input to the vertical structure submodel, along with a function describing the vertical distribution of eddy viscosity between the bed and the water surface. FaSTMECH assumes that this distribution is parabolic for the lower 20% of the flow depth and constant for the upper portion of the water column, which results in a velocity profile that is logarithmic near the bottom and parabolic well away from the bed [Rattray and Mitsuda, 1974]. The vertical structure submodel calculates downstream and cross-stream components of velocity at discrete points in the vertical and thus provides information on the structure of secondary flows and the effects of secondary circulation on the boundary shear stress field.…”

Section: Flow Modelingmentioning

confidence: 99%

Effect of point bar development on the local force balance governing flow in a simple, meandering gravel bed river

2011

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[1] The patterns of depth, velocity, and shear stress that direct a river's morphologic evolution are governed by a balance of forces. Analyzing these forces, associated with pressure gradients, boundary friction, channel curvature, and along-and across-stream changes in fluid momentum driven by bed topography, can yield insight regarding the establishment and maintenance of stable channel forms. This study examined how components of the local force balance changed as a meandering channel evolved from a simple, flat-bedded initial condition to a more complex bar-pool morphology. A numerical flow model, constrained by measurements of velocity and water surface elevation, characterized the flow field for four time periods bracketing two floods. For each time increment, runs were performed for discharges up to bankfull, and individual force balance components were computed from model output. Formation and growth of point bars enhanced topographic steering effects, which were of similar magnitude to the pressure gradient and centrifugal forces. Convective accelerations induced by the bar reduced the cross-stream pressure gradient, intensified flow toward the outer bank, and routed sediment around the upstream end of the bar. Adjustments in the flow field thus served to balance streamwise transport along the inner bank onto the bar and cross-stream transport into the pool. Even in the early stages of bar development, topographically driven spatial gradients in velocity played a significant role in the force balance at flows up to bankfull, altering the orientation of the shear stress and sediment transport to drive bar growth.Citation: Legleiter, C. J., L. R. Harrison, and T. Dunne (2011), Effect of point bar development on the local force balance governing flow in a simple, meandering gravel bed river,

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Section: Flow Modelingmentioning

confidence: 99%

Effect of point bar development on the local force balance governing flow in a simple, meandering gravel bed river

2011

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“…Intratidal variability can be particularly important for strongly forced salt wedge estuaries, as these can exhibit more variability in currents, stratification, and horizontal density gradients on a tidal time scale than do well and partially mixed estuaries. Early work on salt wedge estuaries focused on steady state dynamics of arrested gravity currents and two‐layer hydraulics with extensions including barotropic net flow and comparisons to laboratory and field experiments [e.g., Armi , 1986; Armi and Farmer , 1986; Benjamin , 1968; Rattray and Mitsuda , 1974]. In subsequent work, field measurements were used to explore the intratidal variability, seasonal progression, and mixing of both strongly and weakly forced salt wedges [e.g., Geyer and Farmer , 1989; Guerrero et al 1997; Ibañez et al , 1997].…”

Section: Introductionmentioning

confidence: 99%

Role of straining and advection in the intratidal evolution of stratification, vertical mixing, and longitudinal dispersion of a shallow, macrotidal, salt wedge estuary

Giddings¹,

Fong²,

Monismith³

2011

J. Geophys. Res.

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[1] A month of flow observations in the Snohomish River Estuary reveals the complex intratidal and fortnightly stratification, mixing, and dispersion dynamics in this macrotidal, shallow, salt wedge estuary system. Both salt wedge propagation and concomitant straining of the density field dominate temporal and spatial variations in stratification leading to intratidal variability of shear and mixing that differs in important ways from observations in partially mixed estuaries. Bottom-generated turbulent kinetic energy production is enhanced during spring tides and acts in concert with straining to counteract advection and minimize vertical stratification during the spring flood tides. This bottom-generated mixing contributes to a buoyancy flux near the top of a well-mixed layer during strong flood tides. During strong ebb tides, interfacial shear production and buoyancy flux occur along the sharp straining-enhanced interface just before the system becomes well mixed. Longitudinal dispersion is less sensitive to the spring/neap cycle yet exhibits strong intratidal variability. Reduced longitudinal dispersion is observed during the large floods relative to the rest of the tidal cycle, behavior we attribute to a lack of vertical shear. Overall, ebb tide advection and straining enhance stratification and longitudinal dispersion and allow for interfacial mixing. Intratidal variability, which varies on the spring/neap scale, is a dominant feature of this estuary, suggesting the importance of intratidal processes and tidally varying mixing coefficients in similar strongly stratified, strongly forced estuaries.Citation: Giddings, S. N., D. A. Fong, and S. G. Monismith (2011), Role of straining and advection in the intratidal evolution of stratification, vertical mixing, and longitudinal dispersion of a shallow, macrotidal, salt wedge estuary,

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“…The simplest models of salt wedge systems treat the tidal flow as a small correction to a steady‐state residual (nontidal) problem [ Rattray and Mitsuda , 1974; Pedersen , 1996; Zhu , 1996; Jirka and Arita , 1987]. The solution is sought for an arrested wedge in equilibrium under tidal mean current and density conditions.…”

Section: Introductionmentioning

confidence: 99%

Interfacial mixing in a highly stratified estuary 1. Characteristics of mixing

Kay

Jay

2003

J. Geophys. Res.

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[1] This article is Part I of a set of papers addressing mixing in a highly stratified estuary. Measurements of interfacial turbulence were made in Columbia River estuary under conditions of moderate river flow and neap tides. A flux correlation method was used to determine buoyancy fluxes, and fits to theoretical velocity and temperature variance spectra were used to measure turbulent kinetic and potential energy dissipation rates. At the measurement site in the interior of the estuary, mixing along the top of the salt wedge is found to occur only on ebb, during periods when the internal Froude number is supercritical. The wedge cannot, therefore, be in a quasiequilibrium state, and vertical mixing plays a dominant role in its ebb retreat. The turbulent Froude number Fr T , which represents the ratio of effects of shear and stratification on the mixing, was found to be close to Fr T % 1 during mixing episodes. This suggests an interplay between shear and buoyancy effects that corresponds to a condition of maximum mixing efficiency À. À is measured using both direct calculations of the buoyancy and dissipation terms in the turbulent kinetic energy (TKE) balance (this estimate of À is referred to as À 0 ), and by estimating the buoyancy term B by its relationship to c T , the dissipation of temperature variance (this estimate of À is referred to as À d ). Averages over several mixing events give À 0 % 0.22 and À d % 0.36. Sources of bias in these measurements result from (1) approximations to the full TKE and available potential energy (APE) balances, (2) empirical constants used in fits of measured spectra in inertial subranges, (3) frame motion, and (4) high-pass filtering. The sign of the biases suggest that 0.22 < À < 0.36. Flood-ebb asymmetry in mixing also results in a time dependent force balance (discussed further by Kay and Jay [2003]). This asymmetry is analyzed using a new method to determine profiles of the momentum balance during ebb mixing events.

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Theoretical analysis of conditions in a salt wedge

Cited by 57 publications

References 5 publications

Effect of point bar development on the local force balance governing flow in a simple, meandering gravel bed river

Effect of point bar development on the local force balance governing flow in a simple, meandering gravel bed river

Role of straining and advection in the intratidal evolution of stratification, vertical mixing, and longitudinal dispersion of a shallow, macrotidal, salt wedge estuary

Interfacial mixing in a highly stratified estuary 1. Characteristics of mixing

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