Editing Barton Springs (section)

==Geology==
Barton Springs is the main discharge point for the Barton Springs segment of the [[Edwards Aquifer]] of Texas, a well known [[karst topography|karst]] aquifer. Geologically, the aquifer is composed of [[limestone]] from the [[Cretaceous period]], about 100 million years old.  [[Fractures]], [[fissures]], [[Channel (geography)|conduits]], and [[cave]]s have developed in this limestone.  Both physical forces, such as [[Fault (geology)|faulting]], and chemical forces, such as dissolution of limestone by infiltrating water, have enlarged these voids.  This results in a karst aquifer made up of limestone with large void spaces. Water then enters the aquifer and fills the voids.<ref>{{cite web |url= http://www.edwardsaquifer.net/barton.html |title= Edwards Aquifer and Barton Springs |author= Eckhardt, Gregg |year= 2009 |publisher= Edwards Aquifer |access-date= Sep 12, 2011}}</ref>

All water discharging from Barton Springs originates as rainfall.  Some of this rain falls directly onto the area of land where the aquifer limestone rock is exposed, which is known as the recharge zone.  Other rainfall enters into creeks that cross the recharge zone, and infiltrates the limestone bedrock. After water enters the aquifer, it flows along the gradients created by differences in hydraulic pressure into the area of lowest hydraulic pressure.  This lowest point of hydraulic pressure is Barton Springs.

===Main spring===
Main Barton Spring/Parthenia is the most famous, yet least visible of the four springs because it is completely submerged by pool water.  Located near the diving board in [[Barton Springs Pool]], the spring's flow is not always visible at the surface.

The main spring discharges an average flow of about {{convert|31|e6USgal|m3}} per day.  The lowest discharge ever recorded was {{convert|9|e6USgal|m3}} per day during the [[1950s Texas drought|drought of the 1950s]], and the highest discharge ever recorded was {{convert|85|e6USgal|m3}} per day during December 1991<ref>{{cite web | url=https://waterdata.usgs.gov/monitoring-location/08155500/#parameterCode=00060&startDT=1991-12-01&endDT=1992-03-31 | title=Barton SPGS at Austin, TX }}</ref> and September 2016<ref>{{cite web | url=https://waterdata.usgs.gov/monitoring-location/08155500/#parameterCode=00060&startDT=2016-07-01&endDT=2016-10-30 | title=Barton SPGS at Austin, TX }}</ref> flooding.  By comparison, a typical domestic in-ground swimming pool holds about {{convert|20,000|USgal|m3}}, and the City of Austin, a city of about 1 million residents, uses about {{convert|120|e6USgal|m3}} per day for its public water supply system.<ref>{{cite web |title=Austin Water Use at Record Low |url=http://www.hillcountryalliance.org/austin-water-use-at-record-low/ |website=Hill Country Alliance |access-date=11 July 2020}}</ref>