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Unconfined aquifers are sometimes also called water table or phreatic aquifers, because their upper boundary is the water table or phreatic surface (see Biscayne Aquifer). Typically (but not always) the shallowest aquifer at a given location is unconfined, meaning it does not have a confining layer (an aquitard or aquiclude) between it and the ...
There are two types of aquifers: confined and unconfined. In confined aquifers, there is an overbearing layer called an aquitard, which contains impermeable materials through which groundwater cannot be extracted. In unconfined aquifers, there is no aquitard, and groundwater can be freely extracted from the surface.
Shallow or unconfined wells are completed in the uppermost saturated aquifer at that location (the upper unconfined aquifer). [citation needed] Deep or confined wells are sunk through an impermeable stratum into an aquifer that is sandwiched between two impermeable strata (aquitards or aquicludes). The majority of deep aquifers are classified ...
The slope of the phreatic surface is assumed to indicate the direction of groundwater movement in an unconfined aquifer. The phreatic zone , below the phreatic surface where rock and soil are saturated with water, is the counterpart of the vadose zone , or unsaturated zone, above.
Aquifers can be unconfined, where the top of the aquifer is defined by the water table, or confined, where the aquifer exists underneath a confining bed. [5] There are three aspects that control the nature of aquifers: stratigraphy, lithology, and geological formations and deposits. The stratigraphy relates the age and geometry of the many ...
Groundwater discharge is the volumetric flow rate of groundwater through an aquifer. Total groundwater discharge, as reported through a specified area, is similarly expressed as: = where Q is the total groundwater discharge ([L 3 ·T −1]; m 3 /s), K is the hydraulic conductivity of the aquifer ([L·T −1]; m/s),
For a confined aquifer or aquitard, storativity is the vertically integrated specific storage value. Specific storage is the volume of water released from one unit volume of the aquifer under one unit decline in head. This is related to both the compressibility of the aquifer and the compressibility of the water itself.
In an unconfined aquifer, the saturated thickness is defined as the vertical distance between the water table surface and the aquifer base. If ∂ h / ∂ z = 0 {\displaystyle \partial h/\partial z=0} , and the aquifer base is at the zero datum, then the unconfined saturated thickness is equal to the head, i.e., b=h .