County to Shore Up Frail Dams
Thursday, February 14, 2008
This spring, Fairfax County and the federal Natural Resources Conservation Service will embark on a pricey effort to shore up three lake dams that have been determined by state engineers to be at a high risk of failing.
Work will begin in April on a $3 million project to shore up the spillway around Royal Lake, and plans are in the works for reconstruction at Woodglen Lake and Lake Barton.
The dams are three of six in the Pohick Creek watershed that were built in the 1970s and 1980s to aid storm-water management by the federal government; they were designed during a time when the county was undergoing rapid development. Paths and trails were added later, and they have become 30- to 40-acre oases for joggers and dog walkers.
The packed-earth dams must be upgraded, however, because they do not meet soil-erosion standards. A heavy rainfall or hurricane could erode the spillway and flood nearby homes and businesses.
"These were created in the 1970s and 1980s as flood control for growing communities as the area was being developed," Supervisor Sharon S. Bulova (D-Braddock) said. "Thirty years later, the federal government is telling us that if the dams were to be built today, the soils in the spillway are not sufficient to hold back a high velocity of water should there be a big storm or hurricane."
The state has granted the county conditional use permits for the dams that require the upgrades.
Officials say that the risk is minimal. A 2001 study by a private engineering firm, however, showed that the overflow spillway of the Woodglen dam could wash away during an extremely heavy rain of 25 to 33 inches over a 24-hour period, and that the dam could be breached. Such an event would jeopardize 157 nearby homes, two major roadways, a railway line, 14 industrial sites, six commercial sites and local utilities, said Dipmani Kumar, project manager for the county.
Work on the Royal Lake project is slated to cost $3 million, about 65 percent from federal funds and the rest from Fairfax.
Neighbors have been concerned about the construction in the neighborhood as well as the loss of 2.5 acres of trees.
The trees have to be cut down to redirect the flow path from the spillway from a row of townhouses that sits in its path, the result of a decades-old planning mix-up, Bulova said.
After federal budget cuts in dam rehabilitation money nationwide, the Natural Resources Conservation Service is reevaluating its budget to try to come up with the funds to cover staff costs for planning and design at Woodglen Lake and Lake Barton, said Wade Biddix, assistant state conservationist for water resources.