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An unconfined aquifer has no impermeable barrier immediately above it, such that the water level can rise in response to recharge. A confined aquifer has an overlying impermeable barrier that prevents the water level in the aquifer from rising any higher. An aquifer in the same geologic unit may be confined in one area and unconfined in another.
This is an accepted version of this page This is the latest accepted revision, reviewed on 24 December 2024. Water located beneath the ground surface An illustration showing groundwater in aquifers (in blue) (1, 5 and 6) below the water table (4), and three different wells (7, 8 and 9) dug to reach it. Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in ...
Aquifers of the United States Withdrawal rates from the Ogallala Aquifer.. This is a list of some aquifers in the United States.. Map of major US aquifers by rock type. An aquifer is a geologic formation, a group of formations, or a part of a formation that contains sufficient saturated permeable material to yield significant quantities of water to groundwater wells and springs.
Aquifers near river systems that are over-pumped have been known to deplete surface water sources as well. Research supporting this has been found in numerous water budgets for a multitude of cities. Research supporting this has been found in numerous water budgets for a multitude of cities.
Many states, especially in the western United States, claim ownership of groundwater and allocate the resource through an appropriative system just as they would any surface right. Typically water rights are appropriated based on each aquifer's sustainable yield, and once all the rights are granted no further permits will be issued. Some states ...
In the relatively rare cases of confined aquifers, an impermeable geologic layer (e.g. clay or calcrete) encloses an aquifer, isolating the water within, sometimes for millennia. More commonly, fossil water is found in arid or semi-arid regions where the climate was significantly more humid in recent geologic history.
Hence the actual amount of water that can be extracted from the unit volume of aquifer by pumping or under the action of gravity is called as specific yield. The fraction of water held back in the aquifer is known as specific retention. Thus it can be said that porosity is the sum of specific yield and specific retention.
The Ogallala Aquifer is used for agriculture in the United States; if the aquifer goes dry, more than $20 billion worth of food and fiber will vanish from the world's markets. [15] The aquifer is being depleted so much faster than it is replenished that, eventually, the aquifer will run dry.