New insights into the Edwards Aquifer—Brackish-water simulation, drought, and the role of uncertainty analysis

Fact Sheet 2016-3002
Prepared in cooperation with the San Antonio Water System
By:  and 



The Edwards aquifer is an important water resource in south-central Texas, providing water for residents, businesses, and ecosystems. The aquifer is a highly complex karst system characterized by areas of rapid groundwater flow, faulted and fractured Cretaceous-age rocks, and multiple water-quality zones. Karst aquifer systems include soluble rocks such as limestone and dolomite that can convey tremendous amounts of water through dissolution-enhanced faults and fractures. Recent sustained droughts (2011–15) have heightened concerns about the possible effects of drought on this vital water resource.

The Edwards aquifer consists of three water-quality zones. The freshwater zone of the Edwards aquifer is bounded to the south by a zone of brackish water (transition zone) where the aquifer transitions from fresh to saline water. The saline zone is downdip from the transition zone. There is concern that a recurrence of extreme drought, such as the 7-year drought from 1950 through 1956, could cause the transition zone to move toward (encroach upon) the freshwater zone, causing production wells near the transition zone to pump saltier water. There is also concern of drought effects on spring flows from Comal and San Marcos Springs. These concerns were evaluated through the development of a new numerical model of the Edwards aquifer.

Suggested Citation

Foster, L.K., and White, J.T., 2016, New insights into the Edwards aquifer—Brackish-water simulation, drought, and the role of uncertainty analysis: U.S. Geological Survey Fact Sheet 2016–3002, 6 p.,

ISSN: 2327-6932 (online)

Study Area

Publication type Report
Publication Subtype USGS Numbered Series
Title New insights into the Edwards Aquifer—Brackish-water simulation, drought, and the role of uncertainty analysis
Series title Fact Sheet
Series number 2016-3002
DOI 10.3133/fs20163002
Year Published 2016
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Texas Water Science Center
Description 6 p.
Country United States
State Texas
Other Geospatial Edwards Aquifer
Online Only (Y/N) Y
Additional Online Files (Y/N) N
Google Analytic Metrics Metrics page
Additional publication details