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The vadose zone, also termed the unsaturated zone, is the part of Earth between the land surface and the top of the phreatic zone, the position at which the groundwater (the water in the soil's pores) is at atmospheric pressure ("vadose" is from the Latin word for "shallow"). Hence, the vadose zone extends from the top of the ground surface to the water table.

Water in the vadose zone has a pressure head less than atmospheric pressure, and is retained by a combination of adhesion (funiculary groundwater), and capillary action (capillary groundwater). If the vadose zone envelops soil, the water contained therein is termed soil moisture. In fine grained soils, capillary action can cause the pores of the soil to be fully saturated above the water table at a pressure less than atmospheric. The vadose zone does not include the area that is still saturated above the water table, often referred to as the capillary fringe. ^[1]

Movement of water within the vadose zone is studied within soil physics and hydrology, particularly hydrogeology, and is of importance to agriculture, contaminant transport, and flood control. The Richards equation is often used to mathematically describe the flow of water, which is based partially on Darcy's law. Groundwater recharge, which is an important process that refills aquifers, generally occurs through the vadose zone from precipitation.

In hydrology

The vadose zone is the undersaturated portion of the subsurface that lies above the groundwater table. The soil and rock in the vadose zone are not fully saturated with water; that is, the pores within them contain air as well as water. The portion of the vadose zone that is inhabited by soil microorganism, fungi and plant roots may sometimes be called the soil carbon sponge.

In some places, the vadose zone is absent, as is common where there are lakes and marshes, and in some places, it is hundreds of meters thick, as is common in arid regions.^[2]

Unlike the aquifers of the underlying water-saturated phreatic zone, the vadose zone is not a source of readily available water for human consumption. It is of great importance in providing water and nutrients that are vital to the soil carbon sponge and the biosphere. It is intensively used for the cultivation of plants, construction of buildings, and disposal of waste.^[2]

The vadose zone is often the main factor controlling water movement from the land surface to the aquifer. Thus, it strongly affects the rate of aquifer recharge and is critical for the use and management of groundwater. Flow rates and chemical reactions in the vadose zone also control whether, where, and how fast contaminants enter groundwater supplies. Understanding of vadose-zone processes is therefore crucial in determining the amount and quality of groundwater that is available for human use.^[2]

In speleology

In speleology, cave passages formed in the vadose zone tend to be canyon-like in shape, as the water dissolves bedrock on the floor of the passage.^[3] Passages created in completely water-filled conditions are called phreatic passages and tend to be circular in cross-section.^[4]

References

^ Freeze, R.A. and Cherry, J.A., 1979. Groundwater. Englewood Cliffs, NJ, Printice-Hall Inc., 604 p.
^ ^a ^b ^c US Geological Survey, Office of Groundwater
^ Caves & Caving: Glossary
^ New Mexico: Bureau of Mines & Mining Bulletin 117 (Part I: Discussion of Deposits and Events)

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+{{Short description|Unsaturated aquifer above the water table}}
 {{Refimprove|date=March 2007}}
 [[Image:Vadose zone.gif|thumb|250px|Cross-section of a hillslope depicting the vadose zone, [[capillary fringe]], [[water table]], and [[phreatic]] or saturated zone. ''(Source: [[United States Geological Survey]].)'']]
+[[File:Water table.svg|thumb|350px|Cross section showing the [[water table]] varying with surface topography as well as a [[perched water table]]]]
-The '''vadose zone''', also termed the  unsaturated zone, is the part of Earth between the land surface and the top of the [[phreatic|phreatic zone]] i.e. the position at which the groundwater (the water in the soil's pores) is at atmospheric pressure ("vadose" is from the [[Latin]] for "shallow"). Hence the vadose zone extends from the top of the ground surface to the water table. Water in the vadose zone has a [[Hydraulic head|pressure head]] less than [[atmospheric pressure]], and is retained by a combination of [[adhesion]] (''funiculary groundwater''), and [[capillary action]] (''capillary groundwater''). If the vadose zone envelops [[soil]], the water contained therein is termed [[soil moisture]]. In fine grained soils, capillary action can cause the pores of the soil to be fully saturated above the water table at a pressure less than atmospheric.  The vadose zone does not include the area that is still saturated above the water table, often referred to as the capillary fringe (Freeze & Cherry, 1979).
+The '''vadose zone''', also termed the  '''unsaturated zone''', is the part of Earth between the land surface and the top of the [[phreatic zone]], the position at which the groundwater (the water in the soil's pores) is at atmospheric pressure ("vadose" is from the [[Latin]] word for "shallow"). Hence, the vadose zone extends from the top of the ground surface to the [[water table]].
+Water in the vadose zone has a [[Hydraulic head|pressure head]] less than [[atmospheric pressure]], and is retained by a combination of [[adhesion]] (''funiculary groundwater''), and [[capillary action]] (''capillary groundwater''). If the vadose zone envelops [[soil]], the water contained therein is termed [[soil moisture]]. In fine grained soils, capillary action can cause the pores of the soil to be fully saturated above the water table at a pressure less than atmospheric. The vadose zone does not include the area that is still saturated above the water table, often referred to as the [[capillary fringe]]. <ref name=Freeze>Freeze, R.A. and Cherry, J.A., 1979. Groundwater. Englewood Cliffs, NJ, Printice-Hall Inc., 604 p.</ref>
 Movement of water within the vadose zone is studied within [[soil physics]] and [[hydrology]], particularly [[hydrogeology]], and is of importance to [[agriculture]], [[contaminant]] transport, and [[flood control]]. The [[Richards equation]] is often used to mathematically describe the flow of water, which is based partially on [[Darcy's law]].  [[Groundwater recharge]], which is an important process that refills aquifers, generally occurs through the vadose zone from precipitation.
+==In hydrology==
-'''In Hydrology'''
+[[File:Vadose Zone.jpg|thumb|left|The sharp contact between the vadose zone (brown oxidized [[mudstone]]) and the underlying [[phreatic zone]] (grey unoxidized mudstone) exposed at a construction site.]]
-The unsaturated zone is the portion of the subsurface above the groundwater table. The soil and rock in this zone contains air as well as water in its pores. In some places the unsaturated zone is absent, as is common where there are lakes and marshes, and in some places it is hundreds of meters thick, as is common in arid regions.
+The vadose zone is the undersaturated portion of the subsurface that lies above the groundwater table. The soil and rock in the vadose zone are not fully saturated with water; that is, the pores within them contain air as well as water. The portion of the vadose zone that is inhabited by soil microorganism, fungi and plant roots may sometimes be called the [[soil carbon sponge]].
+In some places, the vadose zone is absent, as is common where there are lakes and marshes, and in some places, it is hundreds of meters thick, as is common in arid regions.<ref name=USGS />
-Unlike the [http://water.usgs.gov/edu/earthgwaquifer.html aquifers] of the saturated zone below, the unsaturated zone is not a source of readily available water for human consumption. But it is of great importance in providing water and nutrients that are vital to the biosphere, and is intensively used for the cultivation of plants, construction of buildings, and disposal of waste.
+Unlike the [[aquifer]]s of the underlying water-saturated [[phreatic zone]], the vadose zone is not a source of readily available water for human consumption. It is of great importance in providing water and nutrients that are vital to the soil carbon sponge and the [[biosphere]].  It is intensively used for the cultivation of plants, construction of buildings, and disposal of waste.<ref name=USGS />
-Hydrologically, the unsaturated zone is often the main factor controlling water movement from the land surface to the aquifer. Thus it strongly affects the rate of aquifer recharge, critical for the use and management of groundwater. It is often regarded as a filter that removes undesirable substances. To some extent this is true, but a more general fact is that flow rates and chemical reactions in the unsaturated zone control whether, where, and how fast contaminants enter groundwater supplies. Understanding of unsaturated-zone processes is therefore crucial in determining the amount and quality of groundwater that is available for human use.<ref>[http://water.usgs.gov/ogw/unsaturated.html US Geological Survey, Office of Groundwater]</ref>
+The vadose zone is often the main factor controlling water movement from the land surface to the aquifer. Thus, it strongly affects the rate of aquifer recharge and is critical for the use and management of groundwater. Flow rates and chemical reactions in the vadose zone also control whether, where, and how fast contaminants enter groundwater supplies. Understanding of vadose-zone processes is therefore crucial in determining the amount and quality of groundwater that is available for human use.<ref name=USGS>[http://water.usgs.gov/ogw/unsaturated.html US Geological Survey, Office of Groundwater]</ref>
-'''Speleology'''
+==In speleology==
+[[File:Mammoth cave canyon.jpg|thumb|An example of a vadose cave passage in [[Mammoth Cave National Park|Mammoth Cave]], Kentucky]]
 In [[speleology]], [[cave]] passages formed in the vadose zone tend to be canyon-like in shape, as the water dissolves [[bedrock]] on the floor of the passage.<ref>[http://www.uppercumberlandcaving.net/glossary.html Caves & Caving: Glossary]</ref>  Passages created in completely water-filled conditions are called [[phreatic]] passages and tend to be circular in cross-section.<ref>[http://www.nps.gov/history/history/online_books/geology/publications/state/nm/1987-117/sec7-1.htm New Mexico: Bureau of Mines & Mining Bulletin 117 (Part I: Discussion of Deposits and Events)]</ref>
-== See also ==
+==See also==
 {{wiktionary|vadose}}
-*[[Aquifer]]
+* {{annotated link|Aquifer}}
+* {{annotated link|Capillary fringe}}
-* [[Epiphreatic zone]]
+* {{annotated link|Epiphreatic zone}}
-*[[Groundwater]]
+* {{annotated link|Groundwater}}
-*[[Water retention curve]]
+* {{annotated link|Infiltration (hydrology)}}
+* {{annotated link|Phreatic zone}}
+* {{annotated link|Water retention curve}}
+==References==
-== References ==
 {{reflist}}
-* {{cite web | url = http://water.usgs.gov/ogw/unsaturated.html | title = US Geological Survey, Unsaturated Zone | publisher = [[USGS]] | accessdate = 2014-05-01}}
-* {{cite web | url = http://toxics.usgs.gov/definitions/unsaturated_zone.html | title = Unsaturated Zone Definitions Page | publisher = [[USGS]] | accessdate = 2006-07-01}}
-* {{cite web | url = http://wwwrcamnl.wr.usgs.gov/uzf/unsatflow.html | title = Unsaturated Zone Flow: Definitions and Details | publisher = [[USGS]] | accessdate = 2006-07-01 |archiveurl = http://web.archive.org/web/20060524210928/http://wwwrcamnl.wr.usgs.gov/uzf/unsatflow.html <!-- Bot retrieved archive --> |archivedate = 2006-05-24}}
-== Further reading ==
+==Further reading==
-*{{cite web | url = http://water.usgs.gov/ogw/unsaturated.html | title = Unsaturated Zone, US Geological Survey | accessdate = 2014-05-01}}
-*{{cite web | url = http://water.usgs.gov/edu/earthgwaquifer.html | title = Aqiofers, US Geological Survey Water Science School| accessdate = 2014-05-01}}
-*{{cite web | url = http://vzj.scijournals.org/ | title = Vadose Zone Journal | accessdate = 2006-07-01}}
+* {{cite web | url = http://water.usgs.gov/ogw/unsaturated.html | title = Unsaturated Zone | work=[[USGS]] | access-date = 2014-05-01}}
+* {{cite web | url = http://water.usgs.gov/edu/earthgwaquifer.html | title = Aquifers | work=USGS | access-date = 2014-05-01}}
+* {{cite web | url = http://toxics.usgs.gov/definitions/unsaturated_zone.html | title = Unsaturated Zone Definitions Page | work = USGS | access-date = 2006-07-01 | archive-date = 2015-09-08 | archive-url = https://web.archive.org/web/20150908234849/http://toxics.usgs.gov/definitions/unsaturated_zone.html | url-status = dead }}
+* {{cite web | url = http://wwwrcamnl.wr.usgs.gov/uzf/unsatflow.html | title = Unsaturated Zone Flow: Definitions and Details | work = USGS | access-date = 2006-07-01 |archive-url = https://web.archive.org/web/20060524210928/http://wwwrcamnl.wr.usgs.gov/uzf/unsatflow.html <!-- Bot retrieved archive --> |archive-date = 2006-05-24}}
 * {{Cite book
   |title=Handbook of Vadose Zone Characterization & Monitoring
@@ Line 48: / Line 57: @@
 }}
+{{Soil science topics}}
+[[Category:Aquifers]]
+[[Category:Hydrology]]
 [[Category:Hydrogeology]]
+[[Category:Soil mechanics]]
 [[Category:Soil physics]]
-[[Category:Cave geology]]