The water table is the surface where the water pressure head is equal to the atmospheric pressure (where gauge pressure = 0). It may be conveniently visualized as the 'surface' of the subsurface materials that are saturated with groundwater in a given vicinity. However, saturated conditions may extend above the water table as surface tension holds water in some pores below atmospheric pressure. Individual points on the water table are typically measured as the elevation that the water rises to in a well screened in the shallow groundwater.
The groundwater may be from infiltrating precipitation or from groundwater flowing into the aquifer. In areas with sufficient precipitation, water infiltrates through pore spaces in the soil, passing through the unsaturated zone. At increasing depths water fills in more of the pore spaces in the soils, until the zone of saturation is reached. In permeable or porous materials, such as sands and well fractured bedrock, the water table forms a relatively horizontal plane. Below the water table, in the phreatic zone, permeable units that yield groundwater are called aquifers. The ability of the aquifer to store groundwater is dependent on the primary and secondary porosity and permeability of the rock or soil. In less permeable soils, such as tight bedrock formations and historic lakebed deposits, the water table may be more difficult to define.
The water table should not be confused with the water level in a deeper well. If a deeper aquifer has a lower permeable unit that confines the upward flow, then the water level in a well screened in this aquifer may rise to a level that is greater or less than the elevation of the actual water table. The elevation of the water in this deeper well is dependent upon the pressure in the deeper aquifer and is referred to as the potentiometric surface, not the water table.
Other articles related to "water table, water, table":
... Aquifer drawdown or overdrafting and the pumping of fossil water may be a contributing factor to sea-level rise ...
... The water balances are calculated for each reservoir separately as shown in the article Hydrology (agriculture) ... The excess water leaving one reservoir is converted into incoming water for the next reservoir ... The depth of the water table, calculated from the water balances, is assumed to be the same for the whole area ...
... The drainage system designed to evacuate salty water also lowers the water table ... The highest permissible level of the water table (or the shallowest permissible depth) depends on the irrigation and agricultural practices and kind of crops ... In many cases a seasonal average water table depth of 0.6 to 0.8 m is deep enough ...
... A water table is a masonry architectural feature that consists of a projecting course that deflects water running down the face of a building away from lower courses or the foundation ... A water table may be found near the base of a wall or at a transition between materials, such as from stone to brick ... WATER TABLE A projection of lower masonry on the outside of the wall slightly above the ground ...
... bricks thick with English bond below the water table five bricks high and Flemish bond above the water table ... The transition from the water table to the walls contains a row of beveled bricks ... On the east wall is a communion table centered between the windows and tablets of obligatory scripts from left to right, the Lord’s Prayer, the Ten ...
Famous quotes containing the words table and/or water:
“For the elemental creatures go
About my table to and fro,
That hurry from unmeasured mind
To rant and rage in flood and wind....
—William Butler Yeats (18651939)
“He said he couldnt make the boy believe
He could find water with a hazel prong
Which showed how much good school had ever done him.”
—Robert Frost (18741963)