Aquifer: Difference between revisions
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<onlyinclude>An '''aquifer''' is a [[porosity|porous]], water-saturated layer of sand, gravel, or bedrock, which contains [[groundwater]] or has [[material flow|flowing]] groundwater. They are accessible by a well, and provide the world with around 1/4 of its drinking [[water]].</onlyinclude><ref name=hackett>G. Tyler Miller, Jr. and D. Hackett, "Water Resources," in ''Living in the Environment'', 2nd ed. USA: Nelson , 2011, ch.15, pp.323-349</ref> They are located beneath a water table (the border between the zone saturated with water and the zone that is not) and above water-tight layers of rock which prevent the water from seeping out. | <onlyinclude>An '''aquifer''' is a [[porosity|porous]], water-saturated layer of sand, gravel, or bedrock, which contains [[groundwater]] or has [[material flow|flowing]] groundwater. They are accessible by a well, and provide the world with around 1/4 of its drinking [[water]].</onlyinclude><ref name=hackett>G. Tyler Miller, Jr. and D. Hackett, "Water Resources," in ''Living in the Environment'', 2nd ed. USA: Nelson , 2011, ch.15, pp.323-349</ref> They are located beneath a water table (the border between the zone saturated with water and the zone that is not) and above water-tight layers of rock which prevent the water from seeping out. | ||
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*'''Confined aquifers''' are confined on both the top and bottom by impermeable rock, in which the water is often under high pressure and can flow to the surface naturally upon the drilling of a well.<ref name=usgs/> | *'''Confined aquifers''' are confined on both the top and bottom by impermeable rock, in which the water is often under high pressure and can flow to the surface naturally upon the drilling of a well.<ref name=usgs/> | ||
Aquifers are replenished naturally by [[precipitation]], which is known as '''natural recharge'''. Some can be recharged by stream [[run-off]], which is known as '''lateral recharge'''. These processes can occur extremely slowly, with water typically flowing downwards at about 1 [[meter]] or so per year and rarely faster than 0.3 meters (a [[foot]]) a day.<ref name=hackett/> If the drawing of water is done slower than it naturally replenishes, then the aquifer is a renewable source of water. | Aquifers are replenished naturally by [[precipitation]], which is known as '''natural recharge'''. Some can be recharged by stream [[run-off]], which is known as '''lateral recharge'''. These processes can occur extremely slowly, with water typically flowing downwards at about 1 [[meter]] or so per [[year]] and rarely faster than 0.3 meters (a [[foot]]) a day.<ref name=hackett/> If the drawing of water is done slower than it naturally replenishes, then the aquifer is a renewable source of water. | ||
[[File:aquiferimg.png|600px|center|thumb|Figure 1. A diagram portraying the layout of an aquifer and distinguishing between "confined" and "unconfined".<ref>Wikimedia Commons [Online], Available: https://upload.wikimedia.org/wikipedia/commons/c/c7/Groundwater_flow.svg</ref>]] | [[File:aquiferimg.png|600px|center|thumb|Figure 1. A diagram portraying the layout of an aquifer and distinguishing between "confined" and "unconfined".<ref>Wikimedia Commons [Online], Available: https://upload.wikimedia.org/wikipedia/commons/c/c7/Groundwater_flow.svg</ref>]] | ||
Revision as of 20:30, 3 September 2015
An aquifer is a porous, water-saturated layer of sand, gravel, or bedrock, which contains groundwater or has flowing groundwater. They are accessible by a well, and provide the world with around 1/4 of its drinking water.[1] They are located beneath a water table (the border between the zone saturated with water and the zone that is not) and above water-tight layers of rock which prevent the water from seeping out.
Aquifers are sorted into unconfined and confined aquifers:[1]
- Unconfined aquifers have a layer of impermeable rock below them, but are not bounded on the top. This means they are not under pressure, and require the use of a pump to lift out the water.
- Confined aquifers are confined on both the top and bottom by impermeable rock, in which the water is often under high pressure and can flow to the surface naturally upon the drilling of a well.[2]
Aquifers are replenished naturally by precipitation, which is known as natural recharge. Some can be recharged by stream run-off, which is known as lateral recharge. These processes can occur extremely slowly, with water typically flowing downwards at about 1 meter or so per year and rarely faster than 0.3 meters (a foot) a day.[1] If the drawing of water is done slower than it naturally replenishes, then the aquifer is a renewable source of water.
Concerns
There are many concerns with water use from aquifers and how it may affect local geography and ecosystems. Water is often drawn faster from aquifers than they naturally replenish, especially in agriculture intense countries like China, India and the United States, which results in these resources drying up. Withdrawal rates have increased rapidly in the past century, with global water withdrawal increasing sevenfold and per capita water withdrawal being quadrupled.[1]
The over-drawing of water also results in the water tables falling, meaning that one needs to go deeper to find an aquifer.[2] This is often difficult to see happening so it is generally too late to act until damage is already done. The first sign of this is typically dry wells, followed by a loss of water in deeper wells. This has an effect on rural populations who rely on the use of aquifers for their water supply, and indirectly increases the gap between the rich and poor in some areas.[1]
References
- ↑ 1.0 1.1 1.2 1.3 1.4 G. Tyler Miller, Jr. and D. Hackett, "Water Resources," in Living in the Environment, 2nd ed. USA: Nelson , 2011, ch.15, pp.323-349
- ↑ 2.0 2.1 USGS. (August 12, 2015). Aquifers and Groundwater [Online], Available: http://water.usgs.gov/edu/earthgwaquifer.html
- ↑ Wikimedia Commons [Online], Available: https://upload.wikimedia.org/wikipedia/commons/c/c7/Groundwater_flow.svg
