Austin’s cave frontier gets slowly uncovered

Austin is home to a complex of underground aquifers that we know are filled by a system of underground caves. However, if we know that to be the case, why we don’t see caves everywhere?

“Basically, because all of them were filled, historically, on ranch land,” Nico Hauwert, Balcones Canyonland Preserve program manager, explained to the Environmental Commission at its May 16 meeting. As a result, the underground frontier that used to be readily apparent slowly disappeared. “If you wanted to make your land marketable, it wasn’t great to have caves everywhere,” he said. Caves were also plugged to use as surface water ponds and trash dumps and to prevent livestock from falling in.

As a result, by 1990, 20 percent of Austin’s 163 documented caves were filled in or destroyed, leaving environmentally sensitive species and certain neighborhoods in peril.

“A couple of caves had a couple of species in the area, and that was the only place you found them,” explained Hauwert. Furthermore, he added that closing off caves can lead to localized flooding. In both Shady Hollow in Southwest Austin and Tarrytown, filled-in caves have been the source of hyperlocalized floods.

Chuck Lesniak, the city’s environmental officer, noted that the city now requires developers to be more vigilant when constructing around caves than in the past. “Typically if there is a cave opening … we (leave a buffer of) up to 300 feet.” This, he explained, helps protect not only the cave but also its surrounding catchment basin.

These regulations, however, are in great part thanks to 38 years of research and restoration by Hauwert, who said that even after almost four decades, the mystery that is Austin’s cave system is only partially solved.

Since 1979, Hauwert has been working to uncover the underground maze that is the cavern network. “I have mapped about 10 percent of the recharge areas (for the Edwards Aquifer),” Hauwert said. What he has discovered has changed assumptions about our underground water system. According to Hauwert, in 1989 scientists hypothesized it took five years for water to flow from Onion Creek into Barton Springs. In reality, it takes two or three days during the wet season and up to three weeks in high summer.

This then led Hauwert to investigate how long it took the Blanco River to flow into our aquifer. It turns out that it is fast enough that this Hill Country waterway is what largely sustains us during drought periods.

Although much has been discovered thanks to cave-trained volunteers who have worked with Hauwert, he explained that restoration can be difficult because it is almost impossible to know what the system was like before caves were plugged. Plus, according to him, finding the caves can be a “subtle” art.

Due to increasing interest in caves though, in 2012 the Watershed Protection Department hired a team of eight men and women cavers to increase access to recharge and educational resource caves. As a result, several educational caves have been restored and complement the roster of 62 federally permitted caves, including one at Bowie High School. These caves are available to the public for exploration. In 2017, 3,243 individuals toured the newly created educational caves, which reduced traffic pressures on Austin’s federally permitted caves and kept visitors within cave traffic permit requirements.

Hauwert confirmed that even though there is a long way to go, the city has come far in its protection efforts. When asked what the most effective approach to cave restoration is, Hauwert explained that it was simple. “The best thing is to preserve land,” he said. “It works pretty good.”

This story has been changed since publication to reflect the fact that Austin does not get its drinking water from aquifers, as was originally reported..

Photo by Yinan Chen (www.goodfreephotos.com) [Public Domain], via Wikimedia Commons.

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