The focus of the model is to simulate the interaction between freshwater, saline water and the brackish-water transition zone
Scientists have a better understanding of how water flows throughout the San Antonio segment of the Edwards aquifer because of a new U.S. Geological Survey (USGS) groundwater flow model, developed in cooperation with San Antonio Water System.
The Edwards aquifer is one of the most prolific aquifers in the world and it provides more than 50% of the drinking water consumed in the San Antonio and Austin areas. The aquifer supplies water to south-central Texas for residential, recreational, industrial and agricultural uses. Several endangered and threatened species are also sustained by groundwater discharged at Comal, San Marcos and Barton Springs.
“Understanding how groundwater moves is critical in order for decision makers to protect this finite resource,” said Darren Thompson, director of water resources at San Antonio Water System. “You can’t manage what you don’t measure.”
The focus of the new USGS model is to simulate the interaction between freshwater, saline (salt) water and where the two mix, called the brackish-water transition zone. Model results indicate that effects on fresh water during a severe drought, such as the drought-of-record during 1950-56, would be minor.
This model improves on a previous USGS model that did not include analysis of the transition or saline zones. While this new model is capable of making predictions of spring flow, salinity concentrations and water levels in nearby wells, the reliability of these predictions are also measured through use of a tool known as uncertainty analysis, which few groundwater modeling studies currently provide. The model, coupled with uncertainty analysis, improves understanding of the potential effects of severe drought on the movement of water within and between the different water-quality zones.
“While the model shows little potential for movement of brackish water into freshwater, the research suggests there is a need for an improved understanding of some parts of the Edwards aquifer flow system,” said USGS scientist Linzy Brakefield. “Better knowledge of how the aquifer is recharged and the relationship between recharge, pumping and springflow is needed. With the new developments from this study there is potential to develop more accurate models in the future.”