Flowing artesian aquifer

For the confined aquifer, the pressure head becomes more important than the elevation head. As can usually be seen in an artesian aquifer condition, the groundwater may flow from a lower elevation to a higher elevation if the water pressure at the lower elevation is higher. 

Compaction caused by the weight of overlying rocks is called upon to explain the water pressure in deep-seated artesian aquifers (Mazor, 1995). Compaction counteracts through-flow in deep aquifers, as it causes collapse features, and pressurizes the entrapped water. If through-flow would take place, the open ends of the hypothetical aquifer ducts would serve as... 

An often quoted case study (Vogel, 1970) is that of an artesian aquifer in an area near the south coast of South Africa (Fig. 11.8). The decrease in 14C downslope from the aquifer has been taken by the researcher to indicate continuity. One can even calculate the velocity of groundwater flow in the aquifer by selecting two points on the lines of Fig. 11.8, for example, 2 km-4000 years and 18 km-28,000 years. The average flow velocity in the aquifer is... 

Jacob, C.E., 1940. On the flow of water in an elastic artesian aquifer. Eos Transactions American Geophysical Union 21, pp. 574-586... 

Our work in this basin has been concentrated in a much smaller area, north of the Alberta—Montana border. The initial research was designed to investigate the oxygen and deuterium content and major-ion chemistry of groundwater from the Milk River aquifer system (Schwartz and Muehlenbachs, 1979). This very extensive unit is an important artesian aquifer. It is recharged in outcrop areas in the southern part of the study area. Flow is mainly northward down the regional dip. The northern portion of the unit is found at depths greater than 350 m and contains very substantial quantities of natural gas. 

Groundwater Flow Groundwater Divide Inclined Confining Beds Artesian Aquifer... 

Jacob, C.E. (1939). Fluctuations in artesian pressure by passing trains. Trans. AGU 20 666-674. Jacob, C.E. (1940). On the flow of water in an elastic artesian aquifer. Trans. AGU 21 574-586. Jacob, C.E. (1945). The water table in the western and central parts of Long Island NY. US Dept, of the Interior Washington DC. 

In such a case the aquifer and water table are said to be perched. Perched aquifers are usually localized. An unconfined aquifer, often called a water table aquifer or a phreatic aquifer, is bounded above by unsaturated porous media that is in contact with the overlying atmosphere. By contrast, in a confined aquifer, the water-bearing layer is bounded on the top and bottom by low-permeability layers a common example occurs when clay layers separate the confined aquifer from overlying and underl)dng materials. Confined aquifers transmit water much as imconfined aquifers do when water is removed by a well, however, there can be no corresponding drainage of pores or movement of air to fill the space vacated by water, as occurs in an unconfined aquifer. Instead, compression of the confined aquifer, as well as expansion of the water as its pressure is released at the well, accommodate the space previously occupied by water. Flawing artesian aquifers are confined aquifers in which water flows out of wells without any need for pumps. 

The confined type of aquifer has a hydraulic pressure (static head) that is on a higher level than the top of the aquifer. This artesian pressure can sometimes reach above the surface level resulting in self flowing wells (artesian wells). 

Figure 35. Flow of groundwater in an confined aquifer with potential artesian wells...

The water in the saturated zone of the phreatic section of a confined system exerts a hydrostatic pressure that causes water to ascend in wells. In fact, a confined aquifer can often be identified by the observation that water ascends in a borehole to a level higher than the level at which the water was first struck. In extreme cases the water ascends to the surface, constituting an artesian well. This phenomenon of water ascending in a well and flowing by itself was first described in 1750 in the area of Artois, a province in... 

Fig. 2.6 Components of a confined aquifer with through-flow tilted, or folded, water-bearing rock strata, sealed at the top and the base by aquicludes. Each active confined system also has a phreatic section at outcrops of the aquifer rocks. The level of the water table in the phreatic section defines the piezometric head in the confined section. Water ascends in boreholes drilled into confined aquifers. Water reaches the surface in artesian flow in boreholes that are drilled at altitudes lower than the piezometric head.

The level water reaches in an artesian well reflects its pressure, called the piezometric, or confined, water head (Fig 2.6). In boreholes drilled at altitudes that are lower than the piezometric head, water will reach the surface in a jet (or wellhead pressure) with a pressure that is proportional to the difference between the altitude of the wellhead and the piezometric head. The piezometric head is slightly lower than the water level in the relevant phreatic section of the system due to the flow resistance of the aquifer. Confined aquifers often underlay a phreatic aquifer, as shown in Fig. 2.7. The nature of such groundwater systems may be revealed by data measured in boreholes and wells. The water levels in wells 1 and 2 of Fig. 2.7 did not rise after the water was encountered, and both wells reached a phreatic aquifer. Well 3 is artesian, and the drillers account should include the depth in which the water was struck and the depth and nature of the aquiclude. The hydraulic interconnection between well 1 and well 3 may be established by... 

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