Edwards Aquifer

The Edwards Aquifer is one of the most prolific artesian aquifers in the world. Located on the eastern edge of Edwards Plateau in the U.S. state of Texas, it discharges about 900,000 acre feet (1.1 km³) of water a year and directly serves about two million people.^[1] The Edwards Aquifer is also home to several unique and endangered species.

Geography

The aquifer's recharge zone,^[2] where surface water enters the aquifer, follows the Balcones Fault line, from Brackettville (roughly along U.S. Highway 90), through San Antonio, and north to Austin along but a few miles west of Interstate 35. On certain stretches of highway in Austin, signs indicate that the driver is entering or leaving the recharge zone, as the zone's easternmost sits beneath heavy urban and suburban development.

Its contributing zone, where shed water is transported near the surface to the recharge zone, extends about 40 miles (64 km) north of the recharge zone at the west end, and tapers to end at a point in the east. The artesian zone,^[3] where water springs from wells naturally due to the higher elevation of the recharge zone, extends 10•20 miles (16•32 km) south on the west end to only a few miles south on the east end. Across the eastern half of the aquifer, the recharge and artesian zones occupy common area.

Economy

The plentiful water provided by rivers fed from the Edwards Aquifer^[4] is the primary reason Spanish missionaries were able to establish so many missions, like the Alamo Mission in San Antonio. Later, immigrants found the Texas Hill Country welcoming because of the food, energy, and water provided by these rivers. Without this supply in the arid plateau, early colonization would have been far more difficult. Cities^[3] like San Antonio, New Braunfels, and San Marcos have been able to support large populations without the need to develop surface water resources. Farmers and ranchers south of the aquifer benefit greatly or entirely from the irrigation possible from these rivers.

Ecology

The Edwards Aquifer is home to several unique species, including the widemouth blindcat,^[5] the Texas blind salamander,^[6] the robber baron cave harvestman^[7] the helotes mold beetle ^[7] and the robber baron cave spider.^[8] These species actually live in the caves, and are either completely without eyes or their eyes are so underdeveloped that they are essentially eyeless. The springs fed from the aquifer are also home to many unique species, such as the Fountain Darter,^[9] San Marcos Gambusia (which might already be extinct), the San Marcos salamander,^[9] and the Barton Springs Salamander.^[10] Texas Wild Rice^[11] is also found only in the upper San Marcos River.

Recharge Zone

The Aquifer has a recharge zone^[2] of 1,250 square miles. Most of the water (75%-80%) that is in the Aquifer originated from some of the creeks and rivers flowing in the area. Two creeks that flow into the Aquifer are the Cibolo and Helotes Creeks.

See also

Notes

1. ^ Eckhardt, G. (2010). "Numeric Data for Charts and Graphs". The Edwards Aquifer Website. http://www.edwardsaquifer.net/data.html.
2. ^ ^{a b} "Edwards Aquifer Recharge Zone". Texas Commission on Environmental Quality. http://www.tceq.state.tx.us/gis/metadata/edw_tsms_met.html. Retrieved 12 May 2010. Texas Commission on Environmental Quality
3. ^ ^{a b} "The Edwards Aquifer". San Antonio Water System. http://www.saws.org/education/h2o_university/virtual_classroom/edwards.shtml. Retrieved 12 May 2010. San Antonio Water System
4. ^ Mitchell, Sarah Scott; Schmiedeskamp, Carl (2004). The Edwards Aquifer: Hidden Heart of Texas Map. Save Our Springs Alliance. ISBN 978-1586112387.
5. ^ Longley, Glenn: Widemouth Blindcat from the Handbook of Texas Online. Retrieved 12 May 2010. Texas State Historical Association
6. ^ "Texas Blind Salamander". Texas Parks and Wildlife Department. http://www.tpwd.state.tx.us/huntwild/wild/species/endang/animals/reptiles_amphibians/blindsal.phtml. Retrieved 12 May 2010. Texas Parks and Wildlife Department
7. ^ ^{a b} "Texas Endangered Invertebrate Species". Mike Quinn, Texas Entomology. http://www.texasento.net/TXendsp.htm. Retrieved 12 May 2010. Mike Quinn, Texas Entomology
8. ^ "Nine Bexar County Endangered Invertebrate Species". Mike Quinn, Texas Entomology. http://www.texasento.net/bexares.htm. Retrieved 12 May 2010. Mike Quinn, Texas Entomology
9. ^ ^{a b} "Endangered Species of the Edwards Aquifer". Edwards Aquifer. http://www.edwardsaquifer.net/species.html. Retrieved 12 May 2010. Edwards Aquifer
10. ^ "Barton Springs Salamander". City of Austin, Texas. http://www.ci.austin.tx.us/salamander/. Retrieved 12 May 2010. City of Austin, Texas
11. ^ "Texas Wild Rice". Texas Parks and Wildlife Department. http://www.tpwd.state.tx.us/huntwild/wild/species/twildric/. Retrieved 12 May 2010. Texas Parks and Wildlife Department

External links

• Edwards Aquifer Authority
• Handbook of Texas Online, s.v. "EDWARDS UNDERGROUND WATER DISTRICT,"
• Edwards Aquifer Home Page, Gregg Eckhardt
• Endangered Species of the Edwards Aquifer
• Save Our Springs Alliance - Edwards Aquifer Protection Plan
• Greater Edwards Aquifer Alliance

Categories: Aquifers in the United States | Geology of Texas | San Marcos, Texas