Part of the trail at Brushy Creek Lake Park will close, likely in late fall for about one year during construction to modernize the park’s dam and provide trail improvements.In September 2010, Tropical Storm Hermine brought widespread flooding to Williamson County, dropping nearly 11 inches of rain in 24 hours in areas including Cedar Park.[/caption]

In September 2010, Tropical Storm Hermine brought widespread flooding to Williamson County, dropping nearly 11 inches of rain in 24 hours in areas including Cedar Park.

The flooding caused more than 2 feet of water to flow over the auxiliary spillway at Dam No. 7 in Brushy Creek Lake Park in Cedar Park, which was built in 1964. According to the Texas Floodplain Management Association, the flood damaged 687 homes in Williamson County. Of those 687, about 150 had major damage from flooding the homes with about 24 to 48 inches of water. The TFMA report shows 32 houses were destroyed after more than 48 inches of water flooded those homes. To help prevent similar flooding, the Texas Commission on Environmental Quality and the Upper Brushy Creek Water Control and Improvement District, or WCID, began discussing a need for updated flood protection infrastructure. TCEQ regulates all dams operated by the state, including Dam No. 7. "The [dams] were built in the 1950s. Everything was rural. There were no houses downstream, so they were designed as low-hazard dams," WCID Manager Ruth Haberman said. "They are [well] maintained and in good shape, but houses get built downstream and ... we are held to a higher standard. WCID is then required by the [TCEQ] to modernize them in some way and make [the dams] safe for those folks [who live] downstream." Most dams throughout Williamson County have been modernized to meet TCEQ's regulations, and Dam No. 7 is one of the last of the WCID's waiting to be upgraded. The dam, currently in the design phase, awaits approval from TCEQ and the city of Austin, and construction is expected to begin in November or December. Construction could last for about one year, Haberman said. The WCID includes 23 flood-control structures in the watershed of the Brazos River Basin in Williamson County and comprises dams in Austin, Cedar Park, Hutto, Leander and Round Rock. The WCID's projects, including the dam modernization, are funded through property taxes.

Temporary trail closing

During construction approximately 4,000 to 4,300 feet of the 7-mile trail at Brushy Creek Lake Park will close, Cedar Park Parks Director Randy Bell said. The trail is frequented by nearby residents, Haberman said, and to offset any inconvenience of the closing, an alternative trail route opened in late November. The alternate route runs along Brushy Creek Road and into Champion Park, which Bell said is regularly used. "Anytime you close the regional trail, people are so attached to it and it is such a part of their life that it is a disruption," Bell said. "Knowing from experience of trying to do work on it in previous years is the reason we built the alternate route. That will allow continuity for trails when the project starts." Bell said there should not be any other noticeable changes for park users during construction and the canoe launch area on the lake will remain open. During dam construction, Williamson County plans to make minor repairs to the trail, Haberman said. Miguel Villarreal, a Cedar Park resident and an engineer with Travis County, said although the renovations are an inconvenience, they are necessary to meet state requirements, and park users will see a long-term benefit upon completion. Craig Potts, a frequent runner of the trail, said he has lived across the street from the park for about 3 1/2 years and runs the trail four to six times per week. Potts attended a public outreach meeting March 24 to receive information about the trail's closing. "I think it's a necessary thing because that really was a bad situation when we had the flood a few years ago," Potts said. "I think all of us runners realize that they needed to do something. We can live with the alternate [route] until they get it fixed. I think it's going to be really nice when they get it done." The WCID hosted two public open house meetings to inform the public about the renovations.

Dam plans

After Tropical Storm Hermine, the WCID received a grant from the Texas Water Development Board to conduct a comprehensive watershed study, which included identifying problem areas and possible flood protection solutions, Haberman said. The WCID plans to send the data from the study to the Federal Emergency Management Agency, which will review the information and create updated floodplain maps for Williamson County, Haberman said. The current floodplain map models were created in the 1970s and 1980s, she said, and do not reflect the changed environment. The maps also dictate flood insurance rates for residents who live nearby. "It's old data, and this watershed has changed so tremendously," she said. "Williamson County has been one of the most rapidly growing counties for quite a while. All of the development that has happened since those models is not [reflected] on those maps, and so those maps aren't accurate. FEMA and the residents are not fully aware of where the risks are or aren't." Although the new maps have not been released, she said they do not add many new residents to the floodplain areas. The WCID plans to send the maps to FEMA in September, she said. "There is very little negative impact to the residents," she said. "It is just going to be more accurate, more detailed, and it will provide greater benefit not only to the residents but to the communities and cities as they regulate new development." Because of the dam's infrastructure and location, engineers were unable to add any height to the dam to mitigate flooding during the design stage. Austin-based engineering firm Freese and Nichols Inc., which is designing the dam, is creating a design similar to the dam at Lake Brazos in Waco, Texas. Construction crews will excavate the area where the existing spillway is located to make way for the new dam. The spillway is located near a portion of the trail at Brushy Lake Creek Park and is not located near any water, Haberman said. No water would flow through the new dam until a flood with more water than storm Hermine occurs, she said. The labyrinth weir design changes the spillway configuration by increasing the surface area of the dam's spillway. The uniqueness of each floodplain, environment and community makes it difficult to have a standard process for modernizing dams, said Dustin Mortensen, an engineer with Freese and Nichols. "We came up with a more innovative solution than the [Upper Brushy Creek WCID] has used in the past," Mortensen said. "[In the past] they have raised the top of the dam with a concrete wall, but due to the location here in the park and then also just other constraints with the site, this [design] made the most sense." Freese and Nichols hired engineers at the Utah Water Research Laboratory to assist with the design. To build a scale model, a river was diverted into the lab to mimic the probable maximum flood estimation, or the flooding threshold of Dam No. 7, Haberman said. The design was sent to TCEQ and other regulatory agencies for review and once approved, construction can begin on the dam, which must remain functioning during renovation. Warren Samuelson, manager of dam safety at TCEQ, said TCEQ will monitor the construction process and conduct a final inspection upon completion. TCEQ is hosting a dam safety workshop scheduled for June 25 at the J.J. Pickle Research Campus, 10100 Burnet Road, Bldg. 137, in Austin. The workshop, hosted from 8 a.m.-2 p.m., will provide information for professional engineers and interested residents about dam safety and emergency action plans. "[The WCID] has made every effort to address issues for the protection of the people as well as addressing the trails and issues associated with recreational aspects of that particular area," Samuelson said. "They are making an effort to address the community as well as dam safety. They have done a lot of work to ensure the public is taken care of."