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Encyclopedia > Water table
Cross section showing the water table varying with surface topography as well as a perched water table

The water table or phreatic surface is the surface where the water pressure is equal to atmospheric pressure. Image File history File links This is a lossless scalable vector image. ... Image File history File links WaterTable. ... Image File history File links WaterTable. ... Diurnal (daily) rhythm of air pressure in northern Germany (black curve is air pressure) Atmospheric pressure is the pressure at any point in the Earths atmosphere. ...


A sustainable amount of water within a unit of sediment or rock, below the water table, in the phreatic zone is called an aquifer. The ability of the aquifer to store groundwater is dependent on the primary and secondary porosity and permeability. This article does not cite any references or sources. ... An aquifer is an underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, silt, or clay) from which groundwater can be usefully extracted using a water well. ... An aquifer is an underground layer of water-bearing permeable rock or unconsolidated materials (gravel, sand, silt, or clay) from which groundwater can be usefully extracted using a water well. ... Missing main definition------ someone add if you know it please. ... Porosity is a measure of the void spaces in a material, and is measured as a fraction, between 0–1, or as a percentage between 0–100%. The term porosity is used in multiple fields including manufacturing, earth sciences and construction. ... Permeability has several meanings: In electromagnetism, permeability is the degree of magnetisation of a material in response to a magnetic field. ...

Contents

Form

The form of a water table may change and vary due to seasonal changes, topography and structural geology. In undeveloped regions, or areas with high amounts of precipitation, the water table roughly follows the contour of the overlying land surface, and rises and falls with increases or decreases in infiltration. Springs and oases occur when the water table reaches the surface. Springs commonly form on hillsides, where the earth's slanting surface may "intersect" with the water table. Other, unseen springs are found under rivers and lakes, and account for the base-flow water levels in water bodies. For discussion of land surfaces themselves, see Terrain. ... Structural geology is the study of the three dimensional distribution of rock bodies and their planar or folded surfaces, and their internal fabrics. ... See: espionage, urban exploration, entryism, heating, ventilation, and air conditioning. ... For the English rock band, see Oasis (band). ... For the Second World War frigate class, see River class frigate The Murray River in Australia A waterfall on the Ova da Fedoz, Switzerland A river is a large natural waterway. ... Lake Clearwater, Ontario, Canada A lake is a large body of water, usually fresh water, surrounded by land. ...


Surface topography

Within an aquifer, the water table is rarely horizontal, but reflects the surface relief due to the capillary effect in soils, sediments and other porous media. In hilly regions, the variation in gradient give rise to rivers, springs or oases when the water table intersects the surface. It should be noted that the water table does not always mimic the topography due to variations in the underlying geologic structure (i.e. - folded, faulted, fractured bedrock). Loess field in Germany Surface-water-gley developed in glacial till, Northern Ireland Technically, soil forms the pedosphere: the interface between the lithosphere (rocky part of the planet) and the biosphere, atmosphere, and hydrosphere. ... This article or section cites very few or no references or sources. ... In geology, the porosity of a rock or sediment is the proportion of the non-solid volume to the total volume of material, and is defined by the ratio: where Vp is the non-solid volume (pores and liquid) and Vm is the total volume of material, including the solid... For other uses, see River (disambiguation). ... A natural spring on Mackinac Island in Michigan. ... For the English rock band, see Oasis (band). ...


Perched water tables

A perched water table (or perched aquifer) is an aquifer that occurs above the regional water table, in the vadose zone. This occurs when there is an impermeable layer of rock or sediment (aquiclude) or relatively impermeable layer aquitard above the main aquifer but below the surface. If a perched aquifer's flow intersects the Earth's surface, at a valley wall for example, the water is discharged as a spring. The vadose zone, also termed the unsaturated zone, is the portion of Earth between the land surface and the water table, and is thus not considered groundwater (vadose is Latin for shallow). It comprises the unsaturated portion of the soil, regolith or bedrock, as well as the saturated capillary fringe... An aquifer is an underground layer of water-bearing permeable rock, or unconsolidated materials (gravel, sand, silt, or clay) from which groundwater can be usefully extracted using a water well. ... It has been suggested that this article or section be merged with Aquifer. ... A natural spring on Mackinac Island in Michigan. ...


Fluctuations

Seasonal fluctuations in the water table. During the dry season, river beds may dry up.

Image File history File links WTFluctuations. ... Image File history File links WTFluctuations. ...

Seasonal fluctuations

In some regions (Great Britain for example), winter precipitation is often higher than summer precipitation and so the groundwater storage is not recharged in summer. Consequently, the water table is lower in the summer period yearly. This disparity between the level of the winter and summer water table is known as the zone of intermittent saturation, wherein the water table will fluctuate in response to climatic conditions. Winter is one of the four seasons of temperate zones. ... For other uses, see Summer (disambiguation). ...


Long term fluctuations

Fossil water is groundwater that has remained in an aquifer for millennia, and occurs mainly in deserts. Fossil water is non-renewable by present day rainfall due to its depth below the surface, and any extraction ('mining') causes a permanent change in the water table in such regions. Fossil water is groundwater having remained in an aquifer for thousands or more years. ... This article is about arid terrain. ... Chuquicamata, the second largest open pit copper mine in the world, Chile. ...


See also


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