Lake Travis - Westlake Edition | June 2022

WATER Travis County experts urge conservation amid decreasing groundwater supplies


The Trinity Aquifer is one of the most highly used groundwater resources in Texas, covering 21,308 square miles.

150 FOOT+ drop in southwestern Travis County middle Trinity Aquifer groundwater levels since 1978

consistent depletion of groundwater resources of “nonrenewable” water resources. From 1978-2018, the water level in the middle Trinity dropped by 150-200 feet in the area south- west of Bee Cave, according to the data. As water levels in the middle Trinity decline, wells must be dug increasingly deeper to reach groundwater. “At some point, you can’t lower your pump any- more, and you have to get a drill deeper,” Hunt said. “At some point, you’re going to run out of aquifer.” The reason for such slow recharge is not entirely clear; however, recent research pinpoints two fault lines on either side as potential culprits, Hunt said. The Bee Creek Fault Zone and the Mount Bonnell Fault sandwich the area southwest of Bee Cave, effectively isolating the aquifer. The area between the two faults has seen the most significant decrease in groundwater levels over time, accord- ing to the data. “We’re drawing water out of rocks that are bound by faults; they’re constrained,” Hunt said. “Nothing is sure in science, but we think that these two features are part of the inherent reason why these rocks are not all that productive. They’re not going to rebound with the next 10-inch rain.” After its creation by the Texas Legislature in 2017 and approval from voters in 2019, the district now receives funds for research to find out more about groundwater in the region. Hunt and others are now working with The University of Texas to conduct studies on the area to determine more information about groundwa- ter supplies. “Surface water and groundwater are intercon- nected,” district President Richard Scadden said. “You can’t talk about one in isolation to the other. The general supply of water in our area is stressed, and this summer, it’s going to be really stressed if all the predictions are true, and we’re all going to need to conserve.”


Groundwater supplies in southwestern Travis County continue to deplete as local entities struggle to manage a public resource trapped beneath private properties, according to a presentation given at Bee Cave City Hall on June 1 from Brian Hunt, a geolo- gist, hydrologist and director of the Southwestern Travis County Groundwater Conservation District. Groundwater districts conserve, manage and pro- tect groundwater resources within the boundaries of the district, according to the conservation district’s website. The district extends west from Austin and south of Lake Travis. It is the only entity in Texas with some degree of control over groundwater usage, Hunt said. “Surface water is treated as a state resource. Groundwater, water beneath your property, is a private property right,” Hunt said. “How do you manage a private resource that really is a common pool resource? That’s the challenge for any ground- water district in Texas.” Groundwater in the area is provided by the Trinity Aquifer, a limestone water-transmitting and -storing formation extending narrowly through Central and North Texas. Rain, bodies of water and other factors contribute to the level of water in an aquifer, depending on its location. Aquifers take a certain amount of time to replenish their supply of water following use. The Trinity Aquifer is a complex series of geologic deposits consisting of three parts: the upper, middle and lower Trinity aquifers. The upper Trinity is shallow and at surface level, followed by the subsurface middle Trinity and underlying lower Trinity. Wells in the upper Trinity rely heavily on surface water supplies such as rain and may go dry during a drought, but due to their ability to refill quickly, they are considered “renewable” water supplies. The middle and lower levels of the Trinity Aquifer are slower to replenish, Hunt said. This has led to

2,000+ wells


estimated annual water use in Trinity Aquifer

Tracking THE WELLS

Experts estimated over 2,000 wells to exist in southwestern Travis County. Geologists track water-use data to determine where groundwater supplies are going.

Ground level

• 0-300 ft. below ground level • Provides 1.4% of annual groundwater pumped • 301-700 ft. below ground level • Provides 36.3% of annual groundwater pumped • 750-1,050 ft. below ground level • Provides 62.3% of annual groundwater pumped

Upper Trinity

300 ft.

Middle Trinity

700 ft. LESS PERMEABLE LAYER 1,050 ft.

Lower Trinity


Middle Trinity: 532 wells

Lower Trinity: 1,490 wells

Total 2,083 wells

Upper Trinity: 61 wells


Middle Trinity: 523.48 Mgal

Lower Trinity: 897.32 Mgal

Total 1,441.46 Mgal

Upper Trinity: 20.66 Mgal


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