The water table, or phreatic surface, is the level at which the ground water pressure is equal to atmospheric pressure. It may be conveniently visualized as the 'surface' of the ground water in a given vicinity. Groundwater is Water located beneath the Ground surface in Soil pore spaces and in the Fractures of lithologic formations As water infiltrates through pore spaces in the soil, it first passes through the zone of aeration, where the soil is unsaturated. At increasing depths water fills in more spaces, until the zone of saturation is reached. This relatively horizontal plane atop this zone constitutes the 'water table'.

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

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 phreatic zone (from Ancient Greek phrear phreat- "a well" or Zone of saturation, is the area in an Aquifer, below the Water An aquifer is an underground layer of Water -bearing Permeable rock or unconsolidated materials ( Gravel, Sand, Silt, or Clay The ability of the aquifer to store groundwater is dependent on the primary and secondary porosity and permeability. An aquifer is an underground layer of Water -bearing Permeable rock or unconsolidated materials ( Gravel, Sand, Silt, or Clay Groundwater is Water located beneath the Ground surface in Soil pore spaces and in the Fractures of lithologic formations 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% Permeability in the Earth sciences (commonly symbolized as κ, or k) is a measure of the ability of a material (typically a rock or unconsolidated

Form

The form of a water table may change and vary due to seasonal changes, topography and structural geology. Topography ( topo-, "place" and graphia, "writing" is the study of Earth 's Surface features or those of Planets Structural geology is the study of the three dimensional distribution of rock bodies and their planar or folded surfaces and their internal fabrics 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. Infiltration is the process by which water on the ground surface enters the Soil. Springs and oases occur when the water table reaches the surface. In Geography, an oasis (plural oases) or Cienega ( Southwestern United States) is an isolated area of vegetation in a Desert, typically 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. "Riverine" redirects here For the use of that term in Maritime geography, see there A lake (from Latin lacus) is a Terrain feature (or Physical feature) a body of Liquid on the surface of a world that is localized to the

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. Soil, often typeset as SOiL, is a four piece rock band from Chicago Illinois United States founded by Shaun Glass Tom Schofield Tim King and Adam Zadel Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of A porous medium or a porous Material is a Solid (often called frame or matrix permeated by an interconnected network of pores (voids filled with a When water reaches the zone of saturation the movement of the water is no longer vertical, it is horizontal in the direction of the slope of the water table. The slope of the water table stand for the hydraulic gradient, which then depends on the rate at which water is added to the system and the permeability of the material. In hilly regions, the variation in gradient give rise to rivers, springs or oases when the water table intersects the surface. "Riverine" redirects here For the use of that term in Maritime geography, see there A spring is a point where Groundwater flows out of the ground and is thus where the Aquifer surface meets the ground surface In Geography, an oasis (plural oases) or Cienega ( Southwestern United States) is an isolated area of vegetation in a Desert, typically 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)

Perched water tables

A perched water table (or perched aquifer) is an aquifer that occurs above the regional water table, in the vadose zone. The vadose zone, also termed the unsaturated zone, is the portion of Earth between the land surface and the phreatic zone or zone of saturation ("vadose" 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. An aquifer is an underground layer of Water -bearing Permeable rock or unconsolidated materials ( Gravel, Sand, Silt, or Clay An aquifer is an underground layer of Water -bearing Permeable rock or unconsolidated materials ( Gravel, Sand, Silt, or Clay If a perched aquifer's flow intersects the Earth's dry surface, at a valley wall for example, the water is discharged as a spring. A spring is a point where Groundwater flows out of the ground and is thus where the Aquifer surface meets the ground surface

Fluctuations

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

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. See also Kingdom of Great Britain Great Britain (Breatainn Mhòr Prydain Fawr Breten Veur Graet Breetain is the larger of the two main islands Winter is one of the four Seasons of Temperate zones Calculated astronomically, it begins on the Solstice and ends on the Equinox In Meteorology, precipitation (also known as one class of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric Summer is one of the four Temperate Seasons Summer marks the warmest time of year with the longest days 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.

Long term fluctuations

Fossil water is groundwater that has remained in an aquifer for millennia, and occurs mainly in deserts. Fossil water or paleowater is Groundwater that has remained in an Aquifer for millennia A desert is a Landscape or region that receives very little precipitation. Fossil water is non-renewable by present day rainfall due to its depth below the surface, and any extraction (such as mining) causes a permanent change in the water table in such regions. Mining is the extraction of valuable Minerals or other geological materials from the earth usually (but not always from an Ore body

See also

• Groundwater
• Aquifer
• Hydrogeology
• Watertable control
• Origin of water on Earth
• Salinity
• Salinity in Australia