On flow in estuaries PART I A critical review of some studies of slightly stratified estuaries PART Il A slightly stratified turbulent flow (original) (raw)
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Some features of the dynamic structure of a deep estuary
Estuarine, Coastal and Shelf Science, 1983
A boundary layer formulation for the dynamic structure of a deep estuary is developed. Cross-stream averages are used, but the boundary layer structure is shown to depend on the cross-stream geostrophic constraint. A similarity transformation and a weighted residual method are used to derive an approximate solution for the velocity and salinity structure of the upper layer. This solution indicates that, in the central regime of the estuary, outflow extends through the entire halocline. Inflow takes place in a much less stratified lower layer, and mass exchange between the layers is by upwelling. This structure is modified in the outer regime of the estuary, where mixing between the layers develops, and in the inner regime, where a sharp halocline develops and where the dynamics are dominated by river runoff. The implications of the dynamics for the flushing process and for pollutant movement and dispersion are discussed.
Estuarine, Coastal and Shelf Science, 1999
A model to determine advective fluxes of water and salt in three-layer salt wedge estuaries under steady river discharge is presented. This model is a generalization of the Knudsen's two-layer model when applied to highly stratified estuaries. The reason for this is that Knudsen's model neglects the interface and produces biased estimates of the salt fluxes at this layer. A basic assumption of the model is that velocity and salinity have linear profiles across the interface, which is appropriate for such types of estuaries. A physical description of the Ebre estuary is given in terms of river discharge, mean salinity in upper and lower layers, and cross-sectional area of all three layers. These data are introduced into the model in order to obtain estimates of horizontal and vertical fluxes. The equations for horizontal fluxes are: the steady salt and water transport conditions at any cross-section and a flow relation between the three layers. Solving the three mentioned equations, explicit expressions for horizontal fluxes are obtained. Introducing the latter in the salt and water continuity equations of upper and lower layers, vertical fluxes of water and salt at any given compartment along the estuary are obtained. These vertical fluxes among the three layers allow more precise information to be obtained about mixing processes within the estuary. A comparison of the results with those corresponding to the Knudsen's two-layer model shows that the model gives a more accurate estimate of advective fluxes in highly stratified estuaries.
Internal hydraulics and mixing in a highly stratified estuary
Journal of Geophysical Research: Oceans, 2000
Shipboard acoustic Doppler current profiler and conductivity-temperaturedepth data obtained during highly stratified conditions in the Hudson River estuary along a section of variable width and breadth are presented. The observations emphasize tidal period asymmetries in the vertical structure of current and salinity. However, these asymmetries exhibit significant along-channel structure which is determined by channel morphology. During the ebb the flow is linearly sheared, and steep halocline slopes in the vicinity of channel contractions are maintained by momentum advection. A minimum in vertical shear across the pycnocline occurs in channel contractions. During food the pycnocline sharpens and flattens with a middepth velocity maximum embedded in the pycnocline which separates a stratified surface layer from a bottom mixed layer. The along-channel structure in vertical shear is consistent with a lateral vorticity equation. Estimates of Richardson numbers suggest that vertical mixing across the pycnocline is enhanced downstream of channel contractions.
Processes, Morphodynamics, and Facies of Tide-Dominated Estuaries
Principles of Tidal Sedimentology, 2011
As defined in this chapter, an estuary foons during a shoreline transgression and then fills during a progradational phase that is transitional to a delta. The spatial distribu tion of processes, grain sizes and facies within tide-dominated estuaries is predict able in general teons. Tidal currents dominate sedimentation along the axis, with wave-dominated sedimentation occurring along the flanks of the estuary in its outer pan. Tidal energy increases into the estuary but then decreases toward the tidal limit, with a gradual transition to river-dominated sedimentation at its head. The interac tion of the tidal wave with the morphology of the estuary, and with river currents, causes the outer estuary to be flood-dominant, with a net landward movement of sand. By contrast, the inner estuary is ebb-dominant, creating a bedload convergence within the estuary. The axial sandy deposits are typically finest at this location. In transgressive-phase estuaries, the main channel shows a low-high-low pattern of sinuosity, with the tightest bends (sinuosity~2.5) occurring at the bedload conver gence. These bends experience neck cutoff in the transition to the progradational phase of estuary filling. The estuary-mouth region is characterized by cross-bedded sands deposited on elongate sand bars, although wave-generated structures can be imponant in some cases. Estuaries that are down-drift of major rivers have anoma lously muddy outer estuarine deposits. Further landward, upper-flow-regime paral lei lamination can be widespread. The margins of the inner estuary are flanked by muddy salt-marsh and tidal-flat deposits that can contain well-developed tidal rhythmites and evidence of seasonal variations in river discharge.
Journal of Advances in Modeling Earth Systems, 2021
The estuaries are known as "transitional systems" which modulate the freshwater inputs into the sea. Ocean salt water enters the estuary and merge with zero-salinity river streamflow. As result of the local overturning circulation and mixing processes, the net outflow at the estuary mouth is a non-zero salinity outflow, denser and stronger than the river flow itself (MacCready & Geyer, 2010). The literature has widely demonstrated that the riverine release strongly affects the ocean circulation and dynamics from coastal scale (e.g.,
Development of the Turbidity Maximum in a Coastal Plain Estuary
1973
A study of the turbidity maximum in the Rappahannock EstuarY' Virginia was conducted to determine how high concentrations of suspended sediment accumulate to form a maximum. Time-series observations of current velocity, salinity an? suspended sediment over 8 to 18 tidal cycles reveal that the maX~~~~on forms in a convergence of bottom residual currents near the trans: ~ r between fresh and salty water. Sediment supplied mainly by the rlve is transported into the convergence by density currents and accum~-•ng. lates since velocity is nearly zero and settling exceeds upward m~X~ The maximum forms in the middle estuary after freshet or ~lood ing and shifts upstream with a landward shift of the salt intrus~on head and diminished river inflow. At the same time, its intensitYd is reduced by settling out, reduced strength of the convergence an increased mixing. Prime prerequisites for development are a strong convergence and high river inflow. One of the main difficulties in studying partially-mixed estuaries is that river inflow, tidal currents, salinity and sediment distributions are continuously changing and therefore never in a iv steady-state condition. They are subject to wide variations with time due to meteorological disturbances, tidal inequalities and inflow fluctuations. Therefore, to overcome these variations and to detect relatively small differences representing the magnitude of net flow and residual transport, synoptic time-series observations over many tidal cycles are required. By computing net velocities and resultant transport over 8 or more tidal cycles, the variaions can be averaged out and the tidal motions eliminated. The remaining net-non-tidal components of the current then can be related to density effects, bottom geometry and river inflow.
New dimensions in estuary classification
Limnology and Oceanography, 1966
Results of recent theoretical studies are used as a basis for a new two-parameter system of estuarine classification. The classes are delineated by the magnitudes of the relative stratification and circulation parameters associated with changes in the salt balance mechanism. The theoretical results depend on a knowledge of the eddy coefficients of viscosity and diffusivity. Tentative relationships between these coefficients and the bulk parameters of tidal current, river flow, and geomorphology, which are obtained from experimental data, may be used to determine the salinity and net current distributions in partially mixed and well-mixed coastal plain estuaries. l Contribution No.