scholarly journals ESTUARINE CURRENTS AND TIDAL STREAMS

2011 ◽  
Vol 1 (7) ◽  
pp. 28
Author(s):  
Roderick Agnew
Keyword(s):  
Fresh Water ◽  
River Flow ◽  
Salt Water ◽  
Three Dimensional ◽  
Vertical Plane ◽  
Water Layer ◽  
Wave Theory ◽  
Constant Density ◽  
Salt Wedge ◽  
Tidal Streams

Fresh water spreading out from the mouth of a river as it enters a salt sea may preserve its identity for a considerable distance on the surface if wind-generated waves, longshore currents and tidal streams are capable of producing only weak mixing. Fig. 1 shows the three dimensional shape of a fresh-water tongue overlying more dense salt water, derived by Takano (1954) on the assumption of constant eddy viscosity and constant density in the fresh water layer, below which the density increases according to an assumed law, making an asymptotic approach to the density of salt water. Takano's model is thus a water jet entraining salt from around and below it. Salt or brackish water may penetrate along the deep channels of an estuary in the shape of a wedge complementary to the fresh water tongue, the salt wedge retreating seawards as heavy rainfall increases the river discharge, and advancing in dry weather intervals. Tidal streams cause a regular oscillation of both fresh and braok water in flood and ebb directions but the seasonal movements of the sloping boundary between fresh and salt water may still be important in low-lying delta regions. Strong tidal streams lead to intense mixing, when neither a fresh water tongue nor a salt wedge can be distinguished, but the isohalines (salinity contours) preserve the general wedge pattern - see Figs. 3 to 6. In the upper reaches of an estuary it is possible to study the effect of the tidal motion by treating it as a simple harmonic perturbation of the uni-directional river flow. Even in the middle portion of the estuary where there is reversal of the horizontal motion, one may seek a "quasi steady" solution for the net effect (seaward movement of fresh water) while allowing for the increased turbulence due to the tidal action. At the seaward end of the estuary there is little deviation from the astronomical tidal rhythm, so the problem reduces to simple harmonic oscillations of salt water. Higher harmonics may be introduced as an extension of the simple solution. For a first approximation it is sufficient to consider flow in the longitudinal vertical plane, to assume that the pressure distribution is hydrostatic as in long wave theory, and even to neglect inertia terms when investigating net effects.

The evolution of under-ice melt ponds, or double diffusion at the freezing point

1974 ◽  
Vol 64 (3) ◽  
pp. 507-528 ◽  
Author(s):  
Seelye Martin ◽  
Peter Kauffman
Keyword(s):  
Fresh Water ◽  
Sea Water ◽  
Freezing Point ◽  
Salt Water ◽  
Ice Sheet ◽  
Water Layer ◽  
Double Diffusion ◽  
Theoretical Models ◽  
Interfacial Region ◽  
Ice Melt

In an experimental and theoretical study, we model a phenomenon observed in the summer Arctic, where a fresh-water layer at a temperature of 0°C floats both over a sea-water layer at its freezing point and under an ice layer. Our results show that the ice growth in this system takes place in three phases. First, because the fresh-water density decreases upon supercooling, the rapid diffusion of heat relative to salt from the fresh to the salt water causes a density inversion and thereby generates a high Rayleigh number convection in the fresh water. In this convection, supercooled water rises to the ice layer, where it nucleates into thin vertical interlocking ice crystals. When these sheets grow down to the interface, supercooling ceases. Second, the presence of the vertical ice sheets both constrains the temperatureTand salinitysto lie on the freezing curve and allows them to diffuse in the vertical. In the interfacial region, the combination of these processes generates a lateral crystal growth, which continues until a horizontal ice sheet forms. Third, because of theTandsgradients in the sea water below this ice sheet, the horizontal sheet both migrates upwards and increases in thickness. From one-dimensional theoretical models of the first two phases, we find that the heat-transfer rates are 5–10 times those calculated for classic thermal diffusion.

Movements Resulting from Mixing of Stratified Waters

1934 ◽  
Vol 1 (2) ◽  
pp. 133-143 ◽  
Author(s):  
H. B. Hachey
Keyword(s):  
Fresh Water ◽  
Salt Water ◽  
Water Layer ◽  
Surface Movement ◽  
Laboratory Tank ◽  
Mixed Water ◽  
Made In

Experiments in mixing steadily at one end of a laboratory tank an upper fresh water with a lower salt water layer demonstrate surface and bottom movements to the mixing area and an intermediate movement of mixed water away from it, which correspond with observations made in an inlet of the sea into which fresh water discharges. If fresh water is merely added at the mixing area to the tank containing salt water, the outward movement is at the surface, and there is no inward surface movement.

scholarly journals NUMERICAL MODEL FOR DENSITY CURRENTS IN ESTUARIES

1976 ◽  
Vol 1 (15) ◽  
pp. 188 ◽  
Author(s):  
Karsten Fischer
Keyword(s):  
Fresh Water ◽  
Numerical Models ◽  
Salt Water ◽  
Water Discharge ◽  
Physical Models ◽  
Stream Velocity ◽  
Density Currents ◽  
Salt Intrusion ◽  
Salt Wedge ◽  
Flow Models

In the estuarine mixing areas of salt water and fresh water the vertical stream velocity profile generally is strongly affected by the baroclinic forces, giving rise to upstream currents near the bottom. Such reverse currents occur not only in stratified estuaries, but also in estuaries of the well-mixed type |1|, and they may cause problems like strong shoaling areas, salt intrusion, or difficulties when disposing wastes or dredged material |3|. The contributions of the salinity variations to the tidal motion are comparable to the contributions from the fresh water upland discharge |1|. For well-mixed estuaries with negligible fresh water discharge, the tidal velocities and water elevations may be obtained from numerical vertically averaged models or from physical homogeneous-flow models, but for all other conditions or desired results one has to use numerical vertically discretized models or physical inhomogeneous-flow models. As numerical and physical models have different properties and deficiencies, they may be used complementarily rather than concurrently |4|, the farfield regime apparently becoming the domain of numerical models. The increased public and scientific interest in water quality problems led to the development and application of baroclinic numerical tidal models |5, 6| . The present paper is concerned with the question, how well the action of baroclinic forces can be represented by numerical techniques. As a test example, the salt wedge problems is tackled. Studies on salt wedges by means of physical models have been very sucessful |1, 7|, but mathematical approches were confined to analytical solutions for the stationary salt wedge |8 - 10| and simple geometric boundaries only. The numerical approach is free from these restrictions, giving a solution of the complete equations of motion, continuity, and convection-diffusion simultaneously.

scholarly journals Modelling the salinity response to fresh water flow and variable tidal amplitude in an idealized river delta 

2021 ◽  
Author(s):  
Constantinos Matsoukis ◽  
Laurent O. Amoudry ◽  
Lucy Bricheno ◽  
Nicoletta Leonardi
Keyword(s):  
Fresh Water ◽  
Water Flow ◽  
River Flow ◽  
Water Layer ◽  
Tidal Range ◽  
Water Volume ◽  
Human Consumption ◽  
Tidal Amplitude ◽  
Salinity Response ◽  
Advection Diffusion Equation

<p>High salinity values in deltaic regions can be detrimental for agriculture, aquaculture and human consumption. Salinity levels in river deltas could significantly increase due to sea level rise and infrastructure works such as river diversions or dam constructions. River flow and tides have a large influence on salinity concentrations and it is thus important to understand their combined role. In this paper, a 3D model is built for an idealized delta. A series of simulations is carried out to investigate salinity fields developed under the combined action of tidal amplitude and fresh water flow. Simulations are classified based on the ratio between fresh water and tidal range. Both tide influenced and river dominated cases were considered. Results emphasize the importance of tidally driven mixing which can establish fresher conditions in the delta for certain amplitudes. Tidal amplitude increase enhances the flow in the delta and enlarges the fresh water layer thickness and length. On the other hand, the maximum tidal ranges can limit significantly the fresh water volume. The spatiotemporal salinity distribution is described in terms of delta topology and network geometry. Salinity and river discharge were found to be negatively and exponentially correlated by an equation that resembles solutions of the 1D advection-diffusion equation. Large bathymetric differences between delta areas were identified to play a key role on the salinity patterns as they can modify the nature of the extracted relationships and correlations.</p>

scholarly journals TIDAL RESPONSE OF TWO-LAYER FLOW AT A RIVER MOUTH

1976 ◽  
Vol 1 (15) ◽  
pp. 182 ◽  
Author(s):  
Shizuo Yoshida ◽  
Masakazu Kashiwamura
Keyword(s):  
Fresh Water ◽  
Salt Water ◽  
River Mouth ◽  
Intermittent Flow ◽  
Mean Velocity ◽  
Tidal Period ◽  
Salt Wedge ◽  
Tidal Motion ◽  
Layer Flow ◽  
Theoretical Considerations

This paper describes various features of tidal effects on the behavior of a salt wedge and on the mechanism of mixing between the salt water and the fresh water in the vicinity of a river mouth. The studies have been performed through experiments, field observations and theoretical considerations. The condition upon which the fresh water begins to show an intermittent flow-pattern owing to an increase of the tidal action, and the criterion of a transition of the mixing type from negligible into intense, were obtained, with two dimensionless parameters X and 6. The former parameter X is given by A = A0/U0T0, in which T0 is the tidal period, A0 is the tidal amplitude of the sea level, and U0 is the temporal mean velocity of the fresh water at the river mouth. The latter parameter 9 is the so-called Keulegan number. Besides, it came evident that a tidal motion of the salt wedge couldn't be understood without a consideration of the internal wave inside the mouth, which were induced by the tide, in addition to a direct effect of the tide.

scholarly journals MATHEMATICAL MODEL OF SALINITY INTRUSION IN THE DELTA OF THE PO RIVER

1974 ◽  
Vol 1 (14) ◽  
pp. 134 ◽  
Author(s):  
Renzo Dazzi ◽  
Mario Tomasino
Keyword(s):  
Good Description ◽  
Salt Water ◽  
Water Layer ◽  
Interfacial Stress ◽  
Po River ◽  
Thermo Electric ◽  
Salt Wedge ◽  
Stress Coefficient ◽  
Grid Points ◽  
The One

A general numerical model capable of reproducing long inter_ nal waves in stratified fluids has been constructed with the aim of investigating the salt wedge penetration in the Delta of the Po river, where the installation of a 2640 MW thermo-electric plant is foreseen. The working hypothesis of the model, in accordance with the actual phenomenology of the river, is the one-dimensional homogeneous motion of two fluid layers of different density. The main original aspects of the numerical computation are: 1) - The use of two different space steps (1 km for the fresh water layer; 200 m for salt water) simultaneously allowing a good description of internal waves (the velocity of which is much smaller than that of the external ones) and making it possible to work with economic (100 sec) time steps. 2) - The straightforward description of the wedge head, obtained by making it always freely correspond to one of the grid points. The model, which has been tested on actual events, reproduces reality with a very good approximation; it also gives evidence of the small relevance of the interfacial stress coefficient in unstea dy tidal generated motion of the salt wedge.

Estuary Geometric Feature ’s Effecting on Salt-Fresh Water Mixing

2011 ◽  
Vol 52-54 ◽  
pp. 448-456
Author(s):  
Li Rong Yuan ◽  
Xiang Ju Cheng ◽  
Zhen Ren Guo
Keyword(s):  
Fresh Water ◽  
Salt Water ◽  
Three Dimensional ◽  
Longitudinal Distribution ◽  
Geometric Feature ◽  
Salt Water Intrusion ◽  
Cross Sectional ◽  
Salinity Field ◽  
Water Mixing ◽  
Bed Form

A three dimensional unstructured model was established and estuaries with different cross sectional divergence rates and different bed form were designed to study the estuary geometric feature effecting on salt-fresh water mixing in estuary. The model dispersing 3d domain into unstructured triangular and/or quadrangular elements, has good flexibility to simulate complex bank. By analyzing the horizontal and longitudinal distribution attributes of velocity and salinity field, the effects of cross section divergence rate, the bottom elevation of mouth and the slope inside estuary on salt water intrusion in estuary are studied. The result could act as design basis for the engineering projects which will change estuary’s bank shape or bed form such as estuary regulation and channel dredging.

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