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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 ...
The part above the water table is the vadose zone (also called unsaturated zone). The phreatic zone size, color, and depth may fluctuate with changes of season, and during wet and dry periods. [ 1 ] [ 2 ] Depending on the characteristics of soil particles, their packing and porosity, the boundary of a saturated zone can be stable or instable ...
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 ...
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.
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]
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 .
The area is underlain by the C aquifer and Redwall-Muav aquifer. The C aquifer is a water-table aquifer, with a depth of up to 1500 feet to the water table and is dry in the west, except for perched water-bearing zones. It is underlain by the Redwall-Muav, confined and up to 3200 feet below the land surface.