Aquifer - Wikiparency

# Aquifer An **aquifer** is an underground layer of permeable rock or sediment — sand, gravel, uncemented sandstone or fractured rock — that holds [[Groundwater|groundwater]] and yields it to wells at a useful rate.[^theis-water] Pumping a well draws down the water level around it in a cone of depression that keeps widening as long as pumping continues; the Cooper–Jacob form of the Theis solution, s = Q/(4πT)·ln(2.25Tt/(r²S)), describes it in terms of the aquifer's transmissivity T and storativity S.[^zeidouni] Whether an aquifer is confined by a layer of clay above it or open to the surface decides how it is recharged and how quickly it can be depleted. <div class="microsim-player"> <iframe src="https://wikitube-3d-microsims.netlify.app/Aquifer.html" width="100%" height="620" frameborder="0" loading="lazy" sandbox="allow-scripts allow-same-origin" allow="accelerometer; gyroscope" title="Aquifer — p5.js microsim"></iframe> </div> *Microsim (THY-097): pump a well and watch the cone of depression spread from an hour to a year; change the pumping rate and the transmissivity. ILLUSTRATIVE: one well in an infinite uniform confined aquifer.* Videos: [16:9](https://wikitube-3d-microsims.netlify.app/media/Aquifer_16x9.mp4) · [9:16](https://wikitube-3d-microsims.netlify.app/media/Aquifer_9x16.mp4) ## Etymology The word combines the Latin *aqua*, water, and *ferre*, to bear or carry: a layer that carries water. ## Properties An aquifer's usefulness depends on its porosity, how much water it holds, and its permeability or hydraulic conductivity, how easily water moves through it. Transmissivity, the conductivity times the saturated thickness, sets how much water the aquifer can deliver to a well; storativity sets how much water it releases per unit fall in head.[^theis-water][^zeidouni] ### Groundwater recharge Unconfined aquifers are recharged from the surface directly above them. A confined aquifer, bounded by aquitards, is recharged mainly where it intersects the land surface, which may be a long way from its wells.[^theis-water] ## Classification Aquifers are classified by saturation, by the materials around them, by whether they are confined, and by the structure of their pores. ### Aquifers versus aquitards An aquitard is a layer with low hydraulic conductivity — clay, shale, or unfractured igneous and metamorphic rock — that slows groundwater but may leak slowly.[^theis-water] ### Confined versus unconfined An unconfined aquifer has no aquitard above it and is open to the atmosphere and surface waters through connected pores; wells in it are water-table wells. A confined aquifer lies between aquitards; because it is usually inclined away from its recharge area, its water is under more than atmospheric pressure, and in an artesian well the water rises above the local water table — sometimes to flow at the surface. Confined aquifers tend to be depleted by pumping more quickly than unconfined ones because their recharge areas are small.[^theis-water] ### Porous, karst, or fractured Water moves between grains in porous aquifers, through dissolved channels in karst limestone, and along cracks in fractured rock; karst and fractured aquifers can carry water and pollutants very quickly. ## Human use of groundwater Pumping creates a localized drop in the water table around a well, the cone of depression. The cone deepens by the same amount for each tenfold increase in pumping time, and many wells pumping for decades can lower a whole region's water level — groundwater mining, which forces deeper, more expensive wells.[^theis-water][^zeidouni] ## By country or continent Major aquifers under heavy use include the High Plains (Ogallala) Aquifer in the United States and aquifers in the Desert Southwest, Mexico, the Middle East, India and China.[^theis-water] ### United States Around Chicago, pumping from a confined aquifer lowered the water level by up to 250 m (800 ft), and many public suppliers switched to Lake Michigan water.[^theis-water] In the Twin Cities, the Prairie du Chien–Jordan aquifer supplied about 75% of the metropolitan area's groundwater in 1970.[^usgs1973] ## See also - [[Groundwater]] - [[Hydraulic_head]] - [[Porous_medium]] - [[Hydrology]] ## References [^theis-water]: Theis, Tom; Tomkin, Jonathan, eds. (2015). *Sustainability: A Comprehensive Foundation*, ch. 7, module "Water Cycle and Fresh Water Supply." https://open.umn.edu/opentextbooks/textbooks/sustainability-a-comprehensive-foundation [^zeidouni]: Zeidouni, Mehdi (2025). *Petroleum Reservoir Dynamics*, ch. 2 (Darcy equation), §3.3 (radial flow), ch. 8 (transient radial flow and drawdown). LSU Scholarly Repository. https://open.umn.edu/opentextbooks/textbooks/petroleum-reservoir-dynamics [^usgs1973]: Norvitch, R. F.; Ross, T. G.; Brietkrietz, Alex (1973). *Water resources outlook for the Minneapolis–Saint Paul Metropolitan Area, Minnesota*. U.S. Geological Survey Open-File Report 73-203. https://doi.org/10.3133/ofr73203 ### Portal Books - Theis, Tom; Tomkin, Jonathan, eds. (2015). *Sustainability: A Comprehensive Foundation* — [OTL record](https://open.umn.edu/opentextbooks/textbooks/sustainability-a-comprehensive-foundation); on the [[PORTAL_Energy]] shelf. - Zeidouni, Mehdi (2025). *Petroleum Reservoir Dynamics* — [OTL record](https://open.umn.edu/opentextbooks/textbooks/petroleum-reservoir-dynamics); on the [[PORTAL_Energy]] shelf. ## External links - [Upper Midwest Water Science Center](https://www.usgs.gov/centers/upper-midwest-water-science-center), U.S. Geological Survey  *Linked from the [[WT!Thury_Hydrodynamics_Compendium|Thury Hydrodynamics Compendium]], sections 19, Hydrology and 35, Flow through the ground.*   *Connected to the Apex Spine:* Aquifer → [[Hydropower|Hydropower]] — [[WT!Thury_Hydrodynamics_Compendium|Compendium]] section 15, *Hydropower*.   **Microsim — three.js (Wikitube framework):** *Aquifer* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/thury/Aquifer.html" data-title="Aquifer"></div> *Built from `MICROSIM_GUIDE/specs/variants/Aquifer.json`; part of the [[WT!Thury_Hydrodynamics_Compendium|Thury Hydrodynamics Compendium]] set.*  ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Aquifer) : [Wikitube](https://en.wikitube.io/wiki/Aquifer) · pinned revision [1371329698](https://en.wikipedia.org/w/index.php?oldid=1371329698) · 2026-09-10 ## Previous hub tags Hubs: `Life_Physics`, `Systems`. Portals: [[PORTAL_Thury_Hydrodynamics_Apex_Spine]], [[PORTAL_Stock_and_flow]]. --- *Thury station wave · 2026-09-10 · drafted · microsim THY-097 (p5.js) · parent [[Hydrology]].*