Groundwater - Wikiparency

# Groundwater **Groundwater** is the [[Water|water]] that fills the pores and fractures of soil and rock in the saturated zone below the water table. Most of it began as rain or snowmelt that soaked into the ground; it moves slowly downhill toward rivers, lakes, springs and wells, driven by differences in [[Hydraulic_head|hydraulic head]] and resisted by the rock's permeability.[^theis-water] Groundwater is about 30% of the world's fresh water and the largest store of usable fresh water.[^usgs-where] It feeds the steady normal flow of rivers between storms, and in the [[Hydrology|hydrology]] of Minnesota's cities it is the main drinking-water supply.[^usgs1973] <div class="microsim-player"> <iframe src="https://wikitube-3d-microsims.netlify.app/Groundwater.html" width="100%" height="620" frameborder="0" loading="lazy" sandbox="allow-scripts allow-same-origin" allow="accelerometer; gyroscope" title="Groundwater — p5.js microsim"></iframe> </div> *Microsim (THY-096): change the aquifer's conductivity from gravel to clay and the recharge rate; water parcels trace the flow to the stream and the travel time changes from years to thousands of years. ILLUSTRATIVE: one-dimensional Dupuit aquifer.* Videos: [16:9](https://wikitube-3d-microsims.netlify.app/media/Groundwater_16x9.mp4) · [9:16](https://wikitube-3d-microsims.netlify.app/media/Groundwater_9x16.mp4) ## Definition Below the land surface lies the unsaturated zone, where pores contain air and water films; beneath it lies the saturated zone, where water completely fills the pores. The boundary is the water table. Groundwater is the water in the saturated zone; soil moisture is the water in the unsaturated zone.[^theis-water] ## Role in the water cycle Groundwater is the slow reservoir of the land: it receives water from infiltration and releases it to streams, lakes and springs, sustaining their flow between rains. The steady normal flow of river water comes mainly from groundwater.[^theis-water] ### Groundwater recharge Most groundwater originates from rain or snowmelt that infiltrates and moves down to the saturated zone; other sources include seepage from lakes, rivers and wetlands, irrigation and septic systems. Recharge areas, where water soaks in rather than running off, include wetlands and flat vegetated land.[^theis-water] ### Location in aquifers An earth material that can supply water to a well at a useful rate — with high permeability and medium to high porosity, such as sand, gravel, uncemented sandstone or fractured rock — is an [[Aquifer|aquifer]]; one with low hydraulic conductivity, such as clay or shale, is an aquitard.[^theis-water] ## Characteristics Groundwater flows through connected pores, so its movement depends on porosity (how much water the material holds) and permeability (how easily water passes). The water table is not flat but follows the land surface in a subdued way, especially in humid climates, and this "topography" drives flow from uplands to valleys.[^theis-water] The flow obeys Darcy's law: the discharge is proportional to the hydraulic gradient and to the medium's permeability.[^zeidouni] ### Availability Groundwater moves slowly: through sand it may travel metres to tens of metres a year, while through aquitards and deep underground it can take many thousands of years to move short distances.[^theis-water] ## Uses by humans Groundwater supplies drinking water, industry and irrigation; about 90% of the aquifers used for water supply are unconfined.[^theis-water] ## Challenges Heavy pumping, pollution and changing recharge threaten groundwater supplies. ### Overdraft Pumping lowers the water table around a well in a cone of depression; when many wells pump for a long time, the regional water table can fall, a condition called groundwater mining. Pumping around Chicago lowered the water level in the region's confined aquifer by up to 250 m (800 ft), and many suppliers switched to Lake Michigan water.[^theis-water] ### Pollution Because groundwater moves slowly and stays underground a long time, pollution that reaches it is particularly persistent.[^theis-water] ## Groundwater governance Because many users draw on the same aquifer, groundwater is managed through well permits, pumping limits and monitoring of water levels. ## By country Groundwater dependence varies widely; heavy use has depleted aquifers in the U.S. High Plains (Ogallala Aquifer) and Desert Southwest, Mexico, the Middle East, India and China.[^theis-water] ## Minnesota *This section is specific to Wikitube.* The Twin Cities draw on two principal bedrock aquifer systems. A 1973 U.S. Geological Survey outlook found that the Prairie du Chien–Jordan aquifer supplied about 75% of the metropolitan area's groundwater, and that with the deeper Mount Simon–Hinckley it provided about 90% of the groundwater used in 1970.[^usgs1973] ## See also - [[Aquifer]] - [[Hydraulic_head]] - [[Porous_medium]] - [[Water_cycle]] ## 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 [^usgs-where]: U.S. Geological Survey, Water Science School. "Where is Earth's Water?" (table after Shiklomanov, in Gleick, ed., *Water in Crisis*, 1993). https://www.usgs.gov/water-science-school/science/where-earths-water [^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 [^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 ### 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.*   **Microsim — three.js (Wikitube framework):** *Groundwater* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/thury/Groundwater.html" data-title="Groundwater"></div> *Built from `MICROSIM_GUIDE/specs/variants/Groundwater.json`; part of the [[WT!Thury_Hydrodynamics_Compendium|Thury Hydrodynamics Compendium]] set.*  ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Groundwater) : [Wikitube](https://en.wikitube.io/wiki/Groundwater) · pinned revision [1368842319](https://en.wikipedia.org/w/index.php?oldid=1368842319) · 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-096 (p5.js) · parent [[Hydrology]].*