Editing Water table (section)

== Formation ==
The water table may vary due to seasonal changes such as [[Precipitation (meteorology)|precipitation]] and [[evapotranspiration]]. In undeveloped regions with permeable soils that receive sufficient amounts of precipitation, the water table typically slopes toward rivers that act to drain the groundwater away and release the pressure in the aquifer. [[Spring (hydrology)|Spring]]s, [[river]]s, [[lake]]s and [[oasis|oases]] occur when the water table reaches the surface. Groundwater entering rivers and lakes accounts for the base-flow water levels in water bodies.<ref>{{Cite web|url=https://pubs.usgs.gov/circ/circ1139/pdf/part1bb.pdf|title=Ground Water and Surface Water A Single Resource - U.S. Geological Survey Circular 1139|last1=Winter|first1=Thomas C|last2=Harvey|first2=Judson W|date=1998|access-date=25 August 2018}}</ref>

=== Surface topography ===
Within an aquifer, the water table is rarely horizontal, but reflects the surface relief due to the capillary effect ([[capillary fringe]]) in [[soil]]s, [[sediment]]s and other [[porous media]]. In the aquifer, groundwater flows from points of higher pressure to points of lower pressure, and the direction of groundwater flow typically has both a horizontal and a vertical component. The slope of the water table is known as the “hydraulic gradient”, which depends on the rate at which water is added to and removed from the aquifer and the permeability of the material. The water table does not always mimic the topography due to variations in the underlying geological structure (e.g.,&nbsp;folded, faulted, fractured bedrock).

=== Perched water tables ===
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. If a perched aquifer's flow intersects the surface, at a valley wall, for example, the water is discharged as a [[spring (hydrosphere)|spring]].