Groundwater table

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Terms & Synonyms

Groundwater table

Official WHO Definition

Other Definitions

The groundwater table is the the upper limit of the saturated soil body.

Contents

Interpretations and Explanations

Description

Fluctuation of the water table
Fluctuation of the water table

At the groundwater table the water pressure is equal to atmospheric pressure.
Below the groundwater table, the water is under hydrostatic pressure, which is greater than the atmospheric pressure, and it increases with depth just like in a pool.
Above the groundwater table capillary suction prevails and the water pressure is less than atmospheric.

Compared to water in a pool, the groundwater table corresponds to the water surface in the pool. Unlike the soil, a pool does not have capillaries above the water surface and there is no water hanging above it.

In a soil, the zone above the water table is called unsaturated (or vadose) zone. Depending on the moisture content of the unsaturated zone, there is more or less air in it.
Below the groundwater table no air present, unless entrapped or dissolved in the water.

Detection

The level of groundwater table (or groundwater level) can be detected by perforating a hole into the soil until water starts entering it. Then wait until the hole is no longer filling up. The level of the water surface in the hole now equals the level of the groundwater table.
         However, if the perforation, by chance, goes through an impermeable (impervious) soil layer (the aquiclude) below which water occurs under artesian pressure, the driller of the hole may be in for a surprise (because the water suddenly rises up in the hole), and anyway he/she has not detected the water table, as there is none. The underlying aquifer is confined (See "Aquifer types").

Influences

When the water table is too high, there may be a problem of waterlogging. In addition, in semi-arid zones, it may lead too soil salinity.
Waterlogging may call for measures like watertable control, land drainage and salinity control.

References

table WHO-Lexicon page (translations and examples)

See also

Internal links:

External Resources

On line the following references and links may be used:

  • a website on waterlogging and salinity : [1]
  • articles on waterlogging and salinity : [2]
  • questions and answers on waterlogging and salinity : [3]
  • subsurface drainage by pipes and ditches : [4] , and a paper on drain spacing : [5] (PDF)
  • subsurface drainage by wells : [6] , and a paper on well spacing : [7] (PDF)

Attachments

 WTFluctuations.gif

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