Karst Aquifers: Edwards Balcones Fault Zone Aquifer Active
The Edwards aquifer is the most transmissive of all the aquifers in Texas and Oklahoma, with large discharges from springs and from flowing and pumped wells. This aquifer demonstrates karst features such as springs and in-stream sinkholes, as well as endangered species.
The Edwards aquifer is the most transmissive of all the aquifers in Texas and Oklahoma. Large discharges from springs and from flowing and pumped wells attest to the highly permeable nature of the aquifer. The area underlain by the Edwards aquifer is a combination of agricultural and ranch land and areas of dense population, including the cities of Austin in Travis County and San Antonio in Bexar County. It has been designated a sole source aquifer by the U.S. Environmental Protection Agency and is the primary source of water for San Antonio, America's eighth largest city. The aquifer is separated into three parts by a groundwater divide and the Colorado River.
Following deposition of Cretaceous rocks, tectonic movement caused the relative uplift of the Edwards Plateau and subsidence of the Gulf of Mexico, and a number of en echelon, northeastward-trending faults formed along the Balcones Fault Zone. The Edwards aquifer is generally coincident with the fault zone. The downdip boundary of the aquifer is largely fault controlled. As a result of the faulting, the chemical quality of the water in the Edwards aquifer can change abruptly in a very short distance across a zone often referred to as the "saline-water line."
As streams cross the Balcones Fault Zone, water percolates downward along the faults where permeability might be greatly enhanced by partial dissolution of limestone. Secondary sources of recharge are direct infiltration of precipitation that falls on aquifer outcrop areas, internal flow of groundwater from the Trinity aquifer where the Edwards and the Trinity aquifers are juxtaposed, and upward leakage from the underlying Trinity aquifer where an upward vertical head gradient exists. Direct recharge to the aquifer can be quite rapid through sinkholes. Water levels in wells completed in the Edwards aquifer rise immediately and springflows increase quickly after major recharge events, thus attesting to a dynamic flow system and the rapid movement of large volumes of water.
Springs
In-Stream Sinkholes
Featured Studies and Datasets
Aquifer-scale studies and the datasets they produce are a key component to understanding how karst aquifers behave, and the quality of water within them.
- Barton Springs Aquifer Groundwater Quality — Annual summertime sampling of about a dozen groundwater wells, during non-stormflow conditions, for a variety of constituents.
- Barton Springs Characterization — A 2-year water-quality study of the 4th largest spring in Texas, which produced an interpretive report.
- National Water-Quality Assessment, South-Central Texas — A program to describe the status and trends in water quality of a large, representative part of the Nation's surface-water and groundwater resources.
Additional Information
The following websites are additional sources of information about this aquifer:
- The Edwards Aquifer Website (by Gregg Eckhardt)
- Edwards Aquifer Authority
- Barton Springs Edwards Aquifer Conservation District
- San Marcos Salamander Photos - U.S. Fish and Wildlife Service National Digital Library
- Barton Springs Salamander Photos - U.S. Fish and Wildlife Service National Digital Library
Below are other science projects associated with karst aquifers.
Karst Aquifers
Karst Aquifers: Valley and Ridge, Piedmont, and Blue Ridge Aquifers
Below are publications associated with this karst aquifer.
Anthropogenic contaminants as tracers in an urbanizing karst aquifer
Statistical analyses of hydrologic system components and simulation of Edwards aquifer water-level response to rainfall using transfer-function models, San Antonio region, Texas
Diffuse-flow conceptualization and simulation of the Edwards aquifer, San Antonio region, Texas
Recent (2003-05) water quality of Barton Springs, Austin, Texas, with emphasis on factors affecting variability
Conceptualization and simulation of the Edwards aquifer, San Antonio region, Texas
Quality of sediment discharging from the Barton Springs system, Austin, Texas, 2000-2002
Water quality in south-central Texas, Texas, 1996–98
Monitoring of Selected Water-Quality Constituents Near the Freshwater/Saline-Water Interface of the Edwards Aquifer, July 1996-December 1997
- Overview
The Edwards aquifer is the most transmissive of all the aquifers in Texas and Oklahoma, with large discharges from springs and from flowing and pumped wells. This aquifer demonstrates karst features such as springs and in-stream sinkholes, as well as endangered species.
The Edwards aquifer is the most transmissive of all the aquifers in Texas and Oklahoma. Large discharges from springs and from flowing and pumped wells attest to the highly permeable nature of the aquifer. The area underlain by the Edwards aquifer is a combination of agricultural and ranch land and areas of dense population, including the cities of Austin in Travis County and San Antonio in Bexar County. It has been designated a sole source aquifer by the U.S. Environmental Protection Agency and is the primary source of water for San Antonio, America's eighth largest city. The aquifer is separated into three parts by a groundwater divide and the Colorado River.
Following deposition of Cretaceous rocks, tectonic movement caused the relative uplift of the Edwards Plateau and subsidence of the Gulf of Mexico, and a number of en echelon, northeastward-trending faults formed along the Balcones Fault Zone. The Edwards aquifer is generally coincident with the fault zone. The downdip boundary of the aquifer is largely fault controlled. As a result of the faulting, the chemical quality of the water in the Edwards aquifer can change abruptly in a very short distance across a zone often referred to as the "saline-water line."
As streams cross the Balcones Fault Zone, water percolates downward along the faults where permeability might be greatly enhanced by partial dissolution of limestone. Secondary sources of recharge are direct infiltration of precipitation that falls on aquifer outcrop areas, internal flow of groundwater from the Trinity aquifer where the Edwards and the Trinity aquifers are juxtaposed, and upward leakage from the underlying Trinity aquifer where an upward vertical head gradient exists. Direct recharge to the aquifer can be quite rapid through sinkholes. Water levels in wells completed in the Edwards aquifer rise immediately and springflows increase quickly after major recharge events, thus attesting to a dynamic flow system and the rapid movement of large volumes of water.
Springs
In-Stream Sinkholes
Featured Studies and Datasets
Aquifer-scale studies and the datasets they produce are a key component to understanding how karst aquifers behave, and the quality of water within them.
- Barton Springs Aquifer Groundwater Quality — Annual summertime sampling of about a dozen groundwater wells, during non-stormflow conditions, for a variety of constituents.
- Barton Springs Characterization — A 2-year water-quality study of the 4th largest spring in Texas, which produced an interpretive report.
- National Water-Quality Assessment, South-Central Texas — A program to describe the status and trends in water quality of a large, representative part of the Nation's surface-water and groundwater resources.
Additional Information
The following websites are additional sources of information about this aquifer:
- The Edwards Aquifer Website (by Gregg Eckhardt)
- Edwards Aquifer Authority
- Barton Springs Edwards Aquifer Conservation District
- San Marcos Salamander Photos - U.S. Fish and Wildlife Service National Digital Library
- Barton Springs Salamander Photos - U.S. Fish and Wildlife Service National Digital Library
- Science
Below are other science projects associated with karst aquifers.
Karst Aquifers
Karst terrain is created from the dissolution of soluble rocks, principally limestone and dolomite. Karst areas are characterized by distinctive landforms (like springs, caves, sinkholes) and a unique hydrogeology that results in aquifers that are highly productive but extremely vulnerable to contamination.Filter Total Items: 13Karst Aquifers: Valley and Ridge, Piedmont, and Blue Ridge Aquifers
The carbonate aquifers of the Appalachian Valley and Ridge Province, formed during Appalachian mountain building, have highly variable karst aquifer characteristics. The Valley and Ridge, Piedmont, and Blue Ridge Aquifers demonstrate karst features such as caves, sinkholes, sinking streams, and conduits. - Publications
Below are publications associated with this karst aquifer.
Filter Total Items: 20Anthropogenic contaminants as tracers in an urbanizing karst aquifer
Karst aquifers are uniquely vulnerable to contamination. In the Barton Springs segment of the karstic Edwards aquifer (Texas, U.S.A.), urban contaminants such as pesticides and volatile organic compounds frequently are detected in spring base flow. To determine whether contaminant concentrations change in response to storms, and if they therefore might act as tracers of focused recharge, samples wAuthorsB. Mahler, N. MasseiStatistical analyses of hydrologic system components and simulation of Edwards aquifer water-level response to rainfall using transfer-function models, San Antonio region, Texas
In 2003 the U.S. Geological Survey, in cooperation with the San Antonio Water System, did a study using historical data to statistically analyze hydrologic system components in the San Antonio region of Texas and to develop transfer-function models to simulate water levels at selected sites (wells) in the Edwards aquifer on the basis of rainfall. Water levels for two wells in the confined zone inAuthorsLisa D. Miller, Andrew J. LongDiffuse-flow conceptualization and simulation of the Edwards aquifer, San Antonio region, Texas
A numerical ground-water-flow model (hereinafter, the conduit-flow Edwards aquifer model) of the karstic Edwards aquifer in south-central Texas was developed for a previous study on the basis of a conceptualization emphasizing conduit development and conduit flow, and included simulating conduits as one-cell-wide, continuously connected features. Uncertainties regarding the degree to which conduitAuthorsR. J. LindgrenRecent (2003-05) water quality of Barton Springs, Austin, Texas, with emphasis on factors affecting variability
From 2003 to 2005, the U.S. Geological Survey, in cooperation with the Texas Commission on Environmental Quality, collected and analyzed water samples from the four springs (orifices) of Barton Springs in Austin, Texas (Upper, Main, Eliza, and Old Mill Springs), with the objective of characterizing water quality. Barton Springs is the major discharge point for the Barton Springs segment of the EdwAuthorsBarbara Mahler, Bradley D. Garner, MaryLynn Musgrove, Amber L. Guilfoyle, Mohan V. RaoConceptualization and simulation of the Edwards aquifer, San Antonio region, Texas
Numerical ground-water flow models for the Edwards aquifer in the San Antonio region of Texas generally have been based on a diffuse-flow conceptualization. That is, although conduits likely are present, the assumption is that flow in the aquifer predominantly is through a network of small fractures and openings sufficiently numerous that the aquifer can be considered a porous-media continuum at tAuthorsK.J. Lindgren, A.R. Dutton, S.D. Hovorka, S.R.H. Worthington, S. PainterQuality of sediment discharging from the Barton Springs system, Austin, Texas, 2000-2002
Four spring outlets of the Barton Springs system provide the only known habitat for the Barton Springs salamander (Eurycea sosorum), a federally listed endangered species. After heavy rainfall, sediment is flushed through the Barton Springs segment of the Edwards aquifer and springflow often becomes turbid (cloudy). Sediment in urban areas often has high concentrations of hydrophobic contaminants,AuthorsBarbara MahlerWater quality in south-central Texas, Texas, 1996–98
This report summarizes major findings about water quality in south-central Texas that emerged from an assessment conducted between 1996 and 1998 by the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program. Water quality is discussed in terms of local and regional issues and compared to conditions found in all 36 NAWQA study areas, called Study Units, assessed to date. FiAuthorsPeter W. Bush, Ann F. Ardis, Lynne Fahlquist, Patricia B. Ging, C. Evan Hornig, Jennifer Lanning-RushMonitoring of Selected Water-Quality Constituents Near the Freshwater/Saline-Water Interface of the Edwards Aquifer, July 1996-December 1997
The Edwards aquifer is the sole source of water for about 1.3 million people in and near San Antonio, Texas, as well as for ranchers and farmers throughout south-central Texas. Because of the demand for this resource, various studies have been conducted to better understand the Edwards aquifer and how the aquifer reacts to environmental changes and human influences. In July 1996, the U.S. GeologicAuthorsJ.R. Cederberg, Patricia B. Ging, Robert T. Ourso