Cities in South and Central Texas have undergone rapid urban expansion that threatens our water supply. According to the U.S. Census Bureau, San Antonio was the fastest growing city in the United States between 2016 and 2017. Austin ranked 12th during the same period. As a result, drastic land use changes throughout San Antonio, Austin and the I-35 corridor were observed via the addition of new housing units, transit construction projects and widespread commercial development.
Justin Guerra, a master’s student in geography and co-investigator in this study, was a previous San Antonio resident. He saw the changes to the city once he relocated and used the population expansion as his motivation for the study.
“Once back, I wanted to participate civically,” Guerra explained. “I learned about the city’s proposed bond for the recharge zone. Later, I took the intro to GIS course at UTSA and saw for myself how land use changed (in the region). Water is essential to human existence. This is what motivated me to focus on the aquifer.”
The UTSA researchers analyzed aquifer protective measures and land-use change trends across different portions of the Edwards Aquifer to better understand the degree to which protective measures influenced aquifer urbanization rates. The National Land Cover Database was used to quantify urban development within the contributing and recharge zones of the Edwards Aquifer across Bexar, Travis, Williamson, Comal, and Hays counties for three time periods: 2001–2006, 2006–2011, and 2011–2016.
The cities of Austin and San Antonio first took active steps to protect the aquifer in the 1970s. However, development continued to occur in sensitive areas, partly due to zoning variances. Austin created the Water Quality Protection Lands (WQPL) program which collectively has issued almost $300 million in bonds for land acquisitions and conservation easements as of 2018.
In San Antonio, there was limited progress in aquifer protection throughout the 1980s, and it was not until 1995 that the Aquifer Protection Ordinance was established. This ordinance also led to the creation of the San Antonio Water System (SAWS) sensitive land acquisition program in 1997, which leveraged water supply fees to preserve the quality and quantity of water recharging the aquifer by purchasing sensitive properties and establishing conservation easements. City residents further supported aquifer protection in 2000 by approving Proposition 3, which involved a one-eighth cent addition to the local sales tax to acquire and protect sensitive areas over the aquifer via the Edwards Aquifer Protection Program (EAPP). The sales tax has been reapproved several times and raised approximately $325 million.
Recently, the aquifer sales tax addition was allowed to expire in 2020, and the sales tax funding was shifted to support workforce development and rapid transit projects. Revenue from SAWS will likely fund the EAPP moving forward, albeit at potentially lower levels.
How both cities approached protecting the aquifer resulted in different rates of urbanization atop the area. The study demonstrates that Bexar County exhibited the greatest reduction in the rate of urbanization within the recharge zone, although the percentage of the zone developed remained the highest. Conversely, the pace of recharge zone development in Travis and Williamson counties decreased less rapidly, but the percentage of the zone urbanized was lower. Limited urban development was observed across the aquifer in Comal and Hays counties during the study period.
Overall, the consistent declining rate of urbanization throughout the sensitive Edwards Aquifer recharge zone suggests that the policies protecting the aquifer were largely effective, particularly given the rapid pace of urban growth throughout the region.
Yet there are specific troubling trends. For example, aquifer urbanization in areas such as Round Rock, Cedar Park, and Leander is worrisome since the only major protected area in the region is Lake Georgetown.
“The lack of protective measures implemented across the northern segment of the aquifer is partly due to Austin focusing its policy efforts primarily on the Barton Springs segment,” Debbage said. “While in Bexar County, expanding aquifer protection efforts in the northeast while also managing the westward expansion of development from the Interstate 10 corridor will likely be pivotal to successfully conserving the Edwards Aquifer landscape within the county.”