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A perched water table (or perched aquifer) is an aquifer that occurs above the regional water table. This occurs when there is an impermeable layer of rock or sediment or relatively impermeable layer above the main water table/aquifer but below the land surface.
The capillary rise of water in a small-diameter tube involves the same physical process. The water table is the level to which water will rise in a large-diameter pipe (e.g., a well) that goes down into the aquifer and is open to the atmosphere.
Cross section showing the water table varying with surface topography as well as a perched water table The phreatic zone , saturated zone , or zone of saturation , is the part of an aquifer , below the water table , in which relatively all pores and fractures are saturated with water.
Cross section showing the water table varying with surface topography as well as a perched water table The vadose zone (from the Latin word for "shallow"), also termed the unsaturated zone , is the part of Earth between the land surface and the top of the phreatic zone , the position at which the groundwater (the water in the soil's pores) is ...
In geotechnical engineering, watertable control is the practice of controlling the height of the water table by drainage.Its main applications are in agricultural land (to improve the crop yield using agricultural drainage systems) and in cities to manage the extensive underground infrastructure that includes the foundations of large buildings, underground transit systems, and extensive ...
Cross section showing the water table varying with surface topography as well as a perched water table Cross-section of a hillslope depicting the vadose zone, capillary fringe, water table, and phreatic or saturated zone (Source: United States Geological Survey)
They mostly consist of unconsolidated sand enclosed by layers of limestone, sandstone or clay and the water is commonly extracted for urban use. The aquifers are replenished by streams and from precipitation and can vary in volume considerably as the water table fluctuates. Being shallow, they are susceptible to contamination by fuel spills ...
The water infiltrates into the ground recharging the local groundwater, because the water table is below the bottom of the stream channel. This is the opposite of a more common gaining stream (or effluent stream ) which increases in water volume farther downstream as it gains water from the local aquifer .