The auxiliary spillways at two more Braddock District lakes need a makeover or else an unlikely 100-year storm could be disastrous for nearby residents.
"That’s not going to happen anytime soon, but we know the issue has to be dealt with," said Supervisor Sharon Bulova (D-Braddock).
Lake Barton, located in Burke Centre, and Woodglen Lake, a Fairfax lake located behind Bonnie Brae Elementary, are two of five county lakes with dams that were built for flood protection in the late 1970s. The state built the dams under the Watershed Protection and Flood Prevention Act of 1954, known simply as PL-566. The act authorized the Secretary of Agriculture to help localities provide flood protection to the sub-basins of identified watersheds within major state river systems, according to the USDA’s National Resources Conservation Service (NRCS) in Virginia. The other three PL-566 damns in the county are Royal Lake, also in the Braddock District; Lake Mercer, just south of Sound Run District Park in Springfield; and Huntsman Lake, located just across the Fairfax County Parkway from South Run District Park.
Bulova toured Woodglen and Lake Barton with officials from NRCS and the county’s department of public works and environmental services Wednesday, March 28. Community members also showed up to get a glimpse of the improvements that will likely begin construction before the end of the decade.
"There are 150 of these dams in the state," said Wade Biddix, assistant state water resources conservationist with NRCS. "Some of them need to be brought up to current design and safety standards."
Both Woodglen and Lake Barton’s auxiliary spillways suffer from permeable, or weak, soils. Last summer, Bulova hosted town meetings for residents near Royal Lake in the Kings Park West community because its spillway also has porous soils. There are no homes in the spillway paths at Lake Barton and Woodglen, as there are at Royal Lake. This removes a lot of the urgency officials felt was necessary for the Royal Lake project.
The dams at the lakes are in good shape, said Biddix. Things have changed in the watershed since they were built, though, and the state dam safety agency is saying the soils won’t withstand a lot of water flowing through, said Biddix. Officials analyze whether the spillway could handle a 100-year storm, which Joseph Seybert, an engineer with NRCS in West Virginia, said has an annual likelihood of about 1 percent.
"We have to look at what’s the best for public safety," said Biddix.
A nearby resident of Lake Barton, Terry Kurtz, asked officials about the surrounding trees during the tour of that lake. She said she hopes the forest at the base of the spillway isn’t impacted by the project.
"As long as we don’t take out our woods," said Kurtz.
Biddix said the state requires the removal of any trees within 25 feet of the slopes of the embankment, which would mean taking out some trees there. At Woodglen, a few trees also look like they would have to be removed, he said, but it would not be many.
AT ROYAL LAKE, engineers and conservationists decided to harden the soil with articulated concrete blocks. The blocks act as reinforcements that coexist with the soil. Gravel is first placed deep into the existing soil, then it is topped with the blocks, more soil and finally sod on the top.
The grass on top is there so the improvements don’t impact the appearance of the spillway, said Seybert, who is assisting the state with these projects. Biddix said the concrete blocks are also likely fixes for both Barton and Woodglen, because virtually the same deficiencies exist at all three lakes: weak soils in the spillways.
Construction at Royal Lake is scheduled to begin sometime in the fall and should take about four months. The process is just beginning for Barton and Woodglen.
"If we could get a draft plan by June, we would have ideas of what some of the best alternative [fixes] would be," said Biddix.
The plan would need to be finalized by September, said Biddix, in order to get the funding in place under the next budget cycle, which is fiscal year 2008. As soon as a plan is engineered, Bulova said she will host a community meeting with all of the details. The public meeting — a required step in the process — would need to happen no later than July in order to remain on schedule for FY '08 funding, said Biddix. NRCS would provide 65 percent and the county provides the other 35 percent.
NRCS also provides funding for desilting or dredging, only if the lake’s storage capacity is less than 50 years, which has not been determined yet. The lakes were built with a 100-year storage capacity, so roughly 30 years of sediment has accumulated, minus some minimal dredging the county used to provide semiregularly more than 15 years ago, said Bulova.
Woodglen has been dredged twice, but not since a "limited dredge" in 1992, said Dipmani Kumar, the Fairfax County project manager in charge of the lake rehabilitations. The storage capacity at Royal Lake was not low enough for federally funded desilting, said Bulova.
Officials have also not determined which lake is a priority. The projects, which are expected to cost about $2 million each, would not happen simultaneously, said Kumar.