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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 (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 ...
Also narrow. A land or water passage that is confined or restricted by its narrow breadth, often a strait or a water gap. nation A stable community of people formed on the basis of a common geographic territory, language, economy, ethnicity, or psychological make-up as manifested in a common culture. national mapping agency A governmental agency which manages, produces, and publishes ...
This glossary of geography terms is a list of definitions of terms and concepts used in geography and related fields, including Earth science, oceanography, cartography, and human geography, as well as those describing spatial dimension, topographical features, natural resources, and the collection, analysis, and visualization of geographic ...
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 Cross-section of a hillslope depicting the vadose zone, capillary fringe, water table, and phreatic or saturated zone (Source: United States Geological Survey)
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 ...