The Edwards Aquifer: The Past, Present, and Future of a Vital Water Resource
CONTAINS OPEN ACCESS

The Edwards aquifer system is one of the great karstic aquifer systems of the world. It supplies water for more than 2 million people and for agricultural, municipal, industrial, and recreational uses. The Edwards (Balcones Fault Zone) Aquifer in the San Antonio, Texas, area was the first to be designated a sole source aquifer by the Environmental Protection Agency in 1975. The Edwards Aquifer also hosts unique groundwater, cave, and spring ecosystems. This 27-chapter memoir reviews the current state of knowledge, current and emerging challenges to wise use of the aquifer system, and some of the technologies that must be adopted to address these challenges.
The Washita Prairie segment of the Edwards (Balcones Fault Zone) Aquifer Available to Purchase
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Published:September 10, 2019
ABSTRACT
The Washita Prairie segment of the Edwards (Balcones Fault Zone) Aquifer is a shallow unconfined aquifer that supports several historical springs, perennial streamflow to Lake Waco, and water for rural households and livestock. Secondary porosity in the aquifer is from neotectonic fractures and epikarst in the Georgetown and Edwards Formations. The fractures produce an “effective” porosity of ~1%. Thin soils allow rapid recharge, as indicated by water-level responses in wells within 24 h of rainfall events. Discharge is generally along second-order streams; topography is the dominant influence on groundwater flow direction. The interbedded clays in the Georgetown Formation create a preferred horizontal to vertical anisotropy. The fractured nature of the aquifer produces local heterogeneity, but regionally, the aquifer acts as a diffuse rather than conduit flow system. Weathering results in a layered flow system with greater effective porosity and permeability in an upper zone compared to the deeper zone. Washita Prairie springs are perennial, with discharges generally <0.05 m3/s. The groundwater is calcium bicarbonate facies with total dissolved solids (TDS) <500 mg/L in most springs and shallow-zone wells. Water quality in deeper wells is more variable, as these encounter the deeper flow system with slower circulation and higher TDS. The shallow water table and rapid recharge through fractures allow surface activities to impact water quality, and nitrate levels appear to be elevated above average background values in places. The Washita Prairie segment of the Edwards (Balcones Fault Zone) Aquifer may be able to supply over 50,000,000 m3 of sustainable water on an annual basis with continued study and proper management.
- anisotropy
- aquifers
- Balcones fault zone
- bicarbonate ion
- Comanchean
- concentration
- Cretaceous
- discharge
- Edwards Aquifer
- Edwards Formation
- epikarst
- fractures
- Georgetown Formation
- ground water
- hydrology
- isotope ratios
- isotopes
- layered materials
- Lower Cretaceous
- Mesozoic
- nitrate ion
- permeability
- preferential flow
- rainfall
- recharge
- reservoir properties
- rivers and streams
- rural environment
- S-34/S-32
- seasonal variations
- segmentation
- shallow aquifers
- springs
- stable isotopes
- sulfur
- sustainable development
- Texas
- unconfined aquifers
- United States
- water management
- water quality
- water supply
- water wells
- weathering
- Lake Waco
- Washita Prairie Segment