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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 (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 ...
A piece of land surrounded by water along the majority of its border while still being connected to a mainland from which it projects. perceptual region An area of the Earth's surface that is defined by a perception of the people living there or by the general society and may not be based on objective data. perched water table perennial stream
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)
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]
Wetlands help maintain the level of the water table and exert control on the hydraulic head. [5] [6] This provides force for groundwater recharge and discharge to other waters as well. The extent of groundwater recharge by a wetland is dependent upon soil, vegetation, site, perimeter to volume ratio, and water table gradient.