Low Flow
Results of Lower Aquifer Pressures in the Texas Hill Country
Low water flow in Cypress Creek at Woodcreek Drive, Wimberley, Texas
Tom Jones
The Blanco River in the Wimberley Valley in Hays County, Texas, provides a key link between surface and subsurface groundwater systems. Central Texas aquifers are critical to supporting agriculture and providing drinking water to millions of people. Economic growth and development in the 1800s and early 1900s relied on abundant water supplies provided by naturally pressurized flowing artesian wells. But in our rapidly urbanizing Hill Country, the Blanco River and the vast groundwater system to which it belongs are failing.
In artesian wells, water—pushed by sufficient water flowing underground behind it—rises within the well to a point above the top of the aquifer. If the water also rises above the ground surface, the well is called a “flowing well,” or “flowing artesian well.” This naturally pressurized upward water flow has always supplied fresh drinking water to the increasing population and to irrigate crops. Artesian wells have also contributed to the protection of our drinking water, stored in the aquifers below, from contamination from surface-borne pollutants.
Map of the Blanco River in Wimberley Valley
In fall of 2023, Central Texas’ largest springs, which come from the Edwards Aquifer, are approaching their lowest flow levels on record, according to Robert Mace, executive director of the Meadows Center for Water and the Environment at Texas State University in San Marcos. Today the lack of flowing springs and wells results from increased water removal—withdrawal by public and private wells and insufficient regulation of water use—resulting in decreased water pressure within the aquifer.
Depressurization impacts an aquifer’s skeletal structure by compression and compaction of the confining formations. So during drought conditions, Pleasant Valley Spring near Wimberley becomes the headwaters of the Blanco River even though the headwaters under wet conditions are about 30 miles upstream! Downstream from Wimberley, Blanco River water enters the Edwards Aquifer. This water, now flowing underground, will eventually re-emerge, discharging at both the San Marcos Springs to the south and Barton Springs to the north.
Lower water levels from depressurization increase the risk of soil subsidence, which further reduces groundwater storage capacity. This is especially relevant in aquifer systems with unconsolidated sediments, such as sand and clay. Subsidence is typically greater in clay layers than in sandstones. Our part of Central Texas is rich in clay soils studded with permeable limestone layers. Drought-contracted clays and water-dissolved limestone conspire to make soils in some areas candidates for subsidence.
Flowing artesian well Photo: Dales Water Services
Historically, observations and measurements of water well levels across the United States demonstrate the widespread decline in flowing artesian conditions over the last century. Bubbling springs and gushing artesian wells were more widespread in the 1800s and early 1900s than they are today. Underground aquifers represented centuries of accumulated captured rainfall, much of it having been stored since the last Ice Age, about 10,000 years ago. Within only a few decades, water pressure had plummeted, and wells stopped flowing freely. Long-term groundwater withdrawals from confined aquifers have been implicated as the primary reason that artesian wells stopped flowing in the Los Angeles Basin, southeastern Michigan, the Dakota Aquifer System (where many wells had stopped flowing by 1910), and in northeastern Texas, where many artesian wells were already dry by 1894!
Ground subsidence above depressurized aquifers always makes the news: cracked building foundations, collapsed homes and roadways—sinkholes! And depressurized aquifer systems, with their reversed vertical groundwater flow direction (like backflow in your fresh water supply line!), have likely increased the potential for contamination in the deep aquifers we all rely on.
And prolonged drought only complicates a bad situation. Here in Central Texas, during periods of extreme drought, when other aquifer recharging streams are dry, the Blanco River can normally provide enough water to the Edwards Aquifer to help maintain flow to Austin homes and to iconic Barton Springs, where generations have swum in crystal spring waters and where endangered species of salamanders—and every other living thing—need sufficient flow of high-quality groundwater.
Decreasing flow in the Blanco River will lead to less recharge to the Edwards Aquifer and result in less discharge from Barton Springs and springs in neighboring San Marcos, New Braunfels, and San Antonio. A better understanding of these aquifer systems and how they are influenced by the Blanco River is important for our management of groundwater in the wider I-35 corridor area, a region for six years now undergoing the nation’s fastest population growth.
“This year’s heat and rainfall conditions rival the intensity of the 1950s’ drought,” said Roland Ruiz, manager of the Edwards Aquifer Authority in San Antonio. Back then, these conditions lingered for almost 10 years. “This drought is not nearly as long in duration, at least not yet,” he said. “In terms of temperature, it’s more intense.”
Taken together—our overdrawn aquifers, unregulated water use, artesian depressurization, reduced spring flow, water well backflow’s possible contamination of the aquifers below and our drinking water here above, soil subsidence and built structure failure, insufficient rainfall for aquifer recharge, and prolonged high heat—all these conditions are a perfect storm threatening the livability and ecology of the Central Texas region. A clear and present danger threatens a part of the world we Texans love. It’s finally time we do what’s necessary, private and public, to keep the Hill Country’s iconic waters flowing.
