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Watershed Protection begins testing to change Waller hydrology

Monday, September 18, 2017 by Jessi Devenyns

After two years of toying with the possibility of emulating the natural hydrology of Austin’s pre-urbanized watersheds through man-made controls, the Watershed Protection Department is finally putting its theories to the test at Reilly Elementary School.

Reilly Elementary sits at the head of the Waller Creek Watershed, a fully urbanized headwaters zone. Due to its location and the impervious cover that was largely developed before water quality control regulations were in place, the zone experiences problems that include erosion and water ponding. In an effort to both study the effects of implementing water storage controls at the headwaters of a fully urbanized watershed and remedy some of the issues experienced in the zone, the Watershed Protection Department hopes to break ground on its field project in December.

The project is based on the findings that the Watershed Protection Department has gathered through modeling exercises examining the changes that water storage controls have on Austin hydrology patterns. During the course of this study, scientists discovered that in areas with impervious cover, capturing water resulted in a favorable reduction in the peak water flows during a storm.

The proposed storage controls also help alleviate the stress of erosion. Ana Gonzales, a senior environmental scientist for the department, explained to the Environmental Commission at its Sept. 6 meeting that these controls allow for a potential reduction of up to 25 percent of impervious cover.

Eventually, the Watershed Protection Department wants to offer these controls citywide to all 167,000 single-family city parcels.

Mateo Scoggins, also a senior environmental scientist for the Watershed Protection Department, explained the initial field application of this project. “What we’re doing in Waller is retro-fitting existing cover. A lot of this is about learning, but this is different from what we would have in CodeNEXT,” he said.

Gonzales further explained the approach saying that they will use cisterns and rain gardens to collect an expected 95 percent of the stormwater. The cisterns, she said, are able to capture rain events that are 1.3 inches or less, which historically encompasses 95 percent of Austin-area storms.

Commissioner Wendy Gordon asked, “Is there some point at which you kind of swing the pendulum too far?”

Scoggins said no. “The idea that we’re going to remove all the water from the watershed is still far out,” he said.

Gonzales said that for water storage controls to have any widespread effect on the watershed, maintenance and participation would be crucial. She noted, “A lot of this is an education process so it becomes a part of what people know what to do. But, this idea of the 167k homes is still far-fetched.”

Despite the general approval for the idea, Commissioner Alesha Istvan cautioned staff to think about reasons why people would not want to participate. She emphasized that the reasons may be broader than economic restrictions.

Gonzales said that the department is interested in equitable outreach and implementation. “We’re thinking hard about it. We don’t have all the answers, but we’re working on it,” she said.

For Scoggins, one of the important educational efforts is making the distinction between this initiative and the separate Waller Creek Tunnel Project that is taking place at the bottom of the watershed. Scoggins told the Austin Monitor that the Watershed Protection Department wasn’t married to the idea of conducting its initial field test in the Waller Creek Watershed. But, due to historical monitoring and its classification as a fully urbanized headwater, Waller Creek was the best candidate for implementation of water storage controls. He did mention that if the controls prove wildly successful, they would change the inflows into the Waller Creek Tunnel for the better.

As a closing thought, Commissioner Pam Thompson brought up the inevitable elephant in the room. “Are you guys changing some of those models because of the climate and the changes that we’ve had?” she asked.

Surprisingly, Gonzales said, “For these exercises that I showed you results of, we did not measure the projections of changes in rainfall.”

However, Scoggins did advise that “the more storage you have, the better you’re going to be in a climate change scenario.”

Photo courtesy of Austin Independent School District.

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