Approximately 80 properties in Round Rock West are set to be moved off the 100-year flood plain—or the area that has a one percent chance to flood any given year—in several years after local officials signed off on a deal to build a dam in Round Rock’s most flood-prone area.
An interlocal agreement between the city of Round Rock and the Upper Brushy Creek Water Control and Improvement District, or WCID, to develop design plans for Dam 101 took effect in January. The deal between the two entities effectively starts the next stage of constructing flooding-prevention infrastructure in the district’s most flood-vulnerable neighborhoods.
The dam, to be located between O’Connor Drive and the Round Rock West neighborhood, has been identified as a need for the area as far back as 1983, according to WCID General Manager Alysha Girard.
“[Round Rock West] is the most significant damage center in our district,” Girard said. “The goal … is to get every structure that is between there and [I-35] out of the 1 percent flood plain.”
Girard expects Dam 101 to cost at least $25 million, and that is not considering the cost of acquiring easements and engineering fees. The dam itself, to be constructed as an earthen feature with a concrete spillway, will be more than a mile long and up to 40 feet tall at some points.
The interlocal agreement, approved by Round Rock City Council and the WCID board of directors in December, follows a similar agreement signed between the two parties in 2014. In that agreement, the WCID agreed to pay the city of Round Rock $2 million for the design of Dam 101 and two other flood-prevention features.
Girard said that once the design work hit the 30 percent completion mark, it became apparent the WCID should take the reins on the design and construction of Dam 101.
“[The agreement] shifts the responsibility and lead of the project back to the [WCID],” Girard said.
The WCID will now finish design on Dam 101, work to acquire necessary land that surrounds the dam and waterway, and file the proper permits. Girard told Community Impact Newspaper that the earliest construction will begin on the dam is summer 2021.
A second, smaller dam dubbed Dam 102 is also wrapped into the proceeding plans, though no funding has been allocated for that infrastructure, either. In all, the WCID and the city of Round Rock aim to remove every household in Round Rock West off the 100-year floodplain with the addition of these two features.
Development pressure in the Austin extraterritorial jurisdiction, or ETJ, west of Round Rock may affect stream flow before the dam is even built, however, according to Girard.
In December, Apple announced the upcoming construction of a $1 billion campus in Northwest Austin. The new campus will be developed just south of a WCID dam along Lake Creek.
Without regional planning, Girard says potential development adds unplanned capacity to waterways, and the WCID has no authority on what can be developed further upstream in Austin’s ETJ.
“A lot of this flood water Round Rock is dealing with is coming from Austin’ jurisdiction,” Girard said.
For now, the WCID will work on finishing the design for Dam 101 and pivot into securing additional funding for the project. As it currently stands, the city of Round Rock and WCID have not dedicated funds for the construction of Dam 101 beyond the $2 million earmarked in the interlocal agreements.