Estuaries tidal flows

An increase has also been observed in the LAS concentration in the aqueous phase during the cold season, due to reduced microbial activity [3,18,23]. Therefore the flow of LAS towards the coastal zone will be strongly influenced by the seasonal variable as confirmed by the values obtained by Takada et al. [3], who found that for the Tamagawa estuary the flow of LAS was five times higher in winter than in summer. However, in long-term monitoring [6,31,32], the variations detected are principally a function of tidal influence and of the time of day, or the day of the week, when the LAS is introduced into the system [6,33],... 

A more benign approach is to extract energy from the tidal flows that occur between headlands and islands or in and out of estuaries. The power available in these tidal streams varies with the cube of the current velocity and while sea currents are typically around 3 m/sec, much lower than the minimum velocities required for wind turbines ( 7m/sec), the density of seawater is such that the output of tidal stream devices is much higher than equivalently sized wind generators. The energy flows are significant with aroimd 7.5 GW of accessible resource in Scotland alone. ... 

Equalizing basin A holding basin in which variations in flow and composition of liquid are averaged. Such basins are used to provide a flow of reasonably uniform volume and composition to a treatment unit. Also called a balancing reservoir. Estuaries Bodies of water which are located at the lower end of a river and are subject to tidal fluctuations. 

Tidal power is normally obtained from the filling and emptying of a bay or an estuary, which may be closed in by a dam. When tidal waters flow through the dam (in either direction), they cause a paddle wheel or turbine to rotate, and this motion generates electricity. 

With regards to solid phase, most of the estuaries are characterized by a "turbidity maximum". The fresh water flow generates an entrainment from the bottom water, the sea water which is entrained from the lower layer by this flow being compensated by a residual landward flow along the bottom. The river-borne particles which settle in this bottom layer are taken up by the residual landward current and trapped in the middle part of the estuary. This process greatly enhances the residence time of particles, especially in tidal estuaries. 

The accumulation of sediments in estuaries appears to be so effective that Meade (1981) has estimated that, "Probably less than 5 percent of all river sediment discharged into the tidal waters of the Atlantic seaboard is deposited on the floor of the continental shelf or the deep sea". These sediments contain an often dramatic imprint of human activity and impact on the estuary and its watershed. But it is an imprint which results not only from the input of materials, but also from the interaction of a great variety of physical, chemical and biological processes in the estuary. We are only beginning to learn to read that record, but the early results suggest that we may learn more about what flows between rivers and the sea from the humble muds on the estuary floor than we can from the water above. 

Low salinity exemplified by freshwater and seawater that are mixed near the estuary of a river flowing into the sea. Tidal flats and lagoons of low salinity are also considered as brackish areas (PIANC, 2000). Volume 2(9). 

Estuary Region of interaction between rivers and near-shore ocean waters, where tidal action and river flow mix fresh and salt water. Such areas include bays, mouths of rivers, salt marshes, and lagoons. These brackish water ecosystems shelter and feed marine life, birds, and wildlife. 

Figure 3.9 Stratification-circulation diagrams used to describe a spectrum of circulation and geomorphometric types of estuaries that can be defined by stratification. Estuarine types are as follows Type 1 estuaries are those without upstream flow requiring tidal transport for salt balance Type 2 estuaries are partially mixed (e.g., Marrows of the Mersey (NM) (UK), James River (J) (USA), Columbia River estuary (C) (USA) Type 3 estuaries are representative of fjords [e.g., Siver Bay (S), Strait of Juan de Fuca (JF) (USA)] and Type 4 estuaries indicative of salt wedge estuaries [e.g., Mississippi River (M) (USA)]. The basic classification parameters are as follows the stratification is defined by SS/Sq where SS is the difference in the salinity between surface and bottom water and So is the mean-depth salinity, both averaged over a tidal cycle and Us/Uf, where U is the surface velocity (averaged over a tidal cycle) and Uf is the vertically averaged net outflow. The subdivisions a and b represent values where SS/Sq <0.1 and SS/Sq >0.1, respectively subscripts h and 1 refer to high and low river flow. The curved line at the top represents the limit of surface freshwater outflow. (From Hansen and Rattray, 1966, as modified by Jay et al., 2000, with permission.)...

Stommel and Farmer (1952) showed that the partitioning of flow at the mouths of estuaries results in higher salinities during flood than ebb flow this will produce a net salt flux in the landward direction. Tidal pumping generally results from a correlation between... 

Hansen and Rattray (1966) introduced a general classification scheme for estuaries based on stratification/circulation that is divided into the following four estuarine types Type 1 estuaries well-mixed estuaries with mean flow in the seaward direction and the salt balance being maintained by diffusive processes—via tidal transport Type 2 estuaries partially mixed estuaries where the net flow reverses at depth and the salt flux is maintained by both diffusive and advective processes Type 3 estuaries these estuaries include fjords with two distinct layers and advection accounting for the majority of the salt flux Type 4 estuaries these are salt-wedge estuaries where freshwater flows out over a stable more dense bottom layer. 

The ETM is defined as a region where the SPM concentrations are considerably higher (10-100 times) than adjacent river or coastal end-members in estuaries. The location of the ETM is generally considered to be controlled by tidal amplitude, volume of river flow, and channel bathymetry. 

The partitioning of trace metals between the dissolved and particulate fractions in estuaries can be affected by variability in river flow, tidal and wind energy, storms, coagulation, and flocculation in the estuarine turbidity maximum (ETM), resuspension events (of sediments and porewaters), and inputs from wetland and mudflat processes. 

Type 1 estuary well-mixed estuaries with mean flow in the seaward direction and the salt balance being maintained by diffusive processes, via tidal transport. 

Valle-Levinson, A., and O Donnell, J. (1996) Tidal interaction with buoyancy-driven flow in a coastal plain estuary. Buoyancy effects on coastal and estuarine dynamics. Coast. Estuar. Stud. 53, 265-281. 

Heinle, D., and Flemer, D. (1976). Flows of materials between poorly flooded tidal marshes and an estuary. Mar. Biol. 35, 359—373. 

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