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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 ( aquiclude ) or relatively impermeable layer ( aquitard ) above the main water table/aquifer but below the land surface.
The definition of the water table is the surface where the pressure head is equal to atmospheric pressure (where gauge pressure = 0). Unsaturated conditions occur above the water table where the pressure head is negative (absolute pressure can never be negative, but gauge pressure can) and the water that incompletely fills the pores of the ...
Cross section showing the water table varying with surface topography as well as a perched water table The vadose zone , 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 at atmospheric pressure ("vadose" is ...
When trapped water in an aquifer is surrounded by layers of impermeable rock or clay, which apply positive pressure to the water, it is known as an artesian aquifer. [1] If a well were to be sunk into an artesian aquifer, water in the well-pipe would rise to a height corresponding to the point where hydrostatic equilibrium is reached. [1]
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.
The low water infiltration rate and hydraulic conductivity may lead to a perched water table form on top of the claypan layer. Water in the perched water table evaporates instead of uptake by plants, especially in the dry season. In the wet season with high precipitation, water can penetrate throughout the soil.
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Groundwater recharge also encompasses water moving away from the water table farther into the saturated zone. [1] Recharge occurs both naturally (through the water cycle ) and through anthropogenic processes (i.e., "artificial groundwater recharge"), where rainwater and/or reclaimed water is routed to the subsurface.