Perched Water

perched water

[′pərcht ′wȯd·ər]
(hydrology)
Groundwater that is unconfined and separated from an underlying main body of groundwater by an unsaturated zone. Also known as perched groundwater.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Perched Water

 

free underground waters that lie the closest to the earth’s surface and have incomplete propagation. Such waters form as a result of the infiltration of atmospheric and surface waters held back by impenetrable or slightly penetrable interfingering layers and lenses or as a result of the condensation of water vapor in rock. They are characterized by seasonal existence. In dry periods they frequently disappear, reappearing in periods of rain or intensive snow melting. They are subject to sharp fluctuations depending on hydrometeorological conditions (the quantity of atmospheric precipitation, the humidity, temperature, and others). Waters that appear at times in swampy formations as a result of excessive feeding of the swamp are also called perched waters. Frequently such waters arise as a result of leaks from water pipes, sewers, swimming pools, and other water-carrying structures, as a result of which the area can become swampy and foundations and basements can flood. In areas where permanetly frozen strata occur, perched water is part of waters above the permafrost. Perched water is usually fresh and weakly mineralized, but it is often polluted by organic substances and has a high content of iron and silicic acid. As a rule, perched water is not a good source for water supplies. However, in cases of necessity measures are taken to artificially preserve it: ponds are built; water is diverted from rivers, guaranteeing a constant supply to the wells being used; vegetation is planted to hold snow runoff; and water-pressure dams are built. In desert regions atmospheric water is drawn off by means of ditches on areas of clayey land (takyry) into nearby sand plots, where a perched-water lens is created, thus forming a certain reserve of fresh water.

REFERENCE

Lebedev, A. F. Pochvennye i gruntovye vody, 4th ed. Moscow, 1936.

A. M. OVCHINNIKOV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The role of hydraulic conductivity in zone B is found critical in the buildup of higher water table zones leading to the land degradation in response to perched water table zones development.
It does not take much rain falling on a building to leak through a cladding and end up with some perched water. We need to put this perched water into perspective.
Among the topics are estimating near-surface shear-wave velocity and quality factor by inverting high-frequency Rayleigh waves, analyzing the velocity dispersion and attenuation behavior of multi-frequency sonic logs, determining electric permittivity and conductivity directly from surface-reflection data from air-launched ground penetrating radar, high-resolution seismic imaging of near-surface fault structures within the Upper Rhine Graben in Germany, and detecting perched water bodies using surface-seismic time-lapse travel-time tomography.
In the experimental Lewis-1 watershed, we installed a weather station, 400 soil-moisture sensors, a perched water monitoring infrastructure and a stream-flow monitoring network.
These little springs are coming from a strange geological feature known as a perched water table, where an impervious layer of rock forms a saucer underground that eventually overflows.
Runoff usually occurs either when the infiltration rate is less than the rainfall intensity (classical Hortonian runoff), or when the soil saturates due to either the true ground water table or a perched water table rising to the surface.
Next to two field-center wells (7, 19) and three ditch-adjacent wells (5, 8, 17), we also installed shallow piezometers to investigate the possibility of perched water tables.
Water perches in the lower zone of soil resulting in a "perched water table" that can cause plant roots to drown and rot.
However, at some time during the process a perched water table was disturbed in the highest gravel and cobble formation, causing water to freely flow through the drilled hole down to the rig site at the south end of the site.
He noted that when the perched water table was snagged and flooding occurred on the south end of the project one of the first options considered was to hammer in a steel casing to isolate the gravel layer at the top end of the bore.
In other cores, the abrupt transition to marl records a localized perched water table during the Chippewa Low.