Rehabilitating the Lake Royal dam will be a team effort.
Supervisor Sharon Bulova (D-Braddock), along with staff members and environmental experts, organized a community meeting Thursday, Sept. 29 to consider different methods of repairing the dam along the southern edge of Lake Royal in Burke. The dam, also known as Pohick Creek Dam Site 4, reached completion in July 1977. According to the Natural Resources Conservation Service (NRCS), a division of the United States Department of Agriculture, the Lake Royal dam is showing its age.
Gannett Fleming, Inc. conducted a study of the dam in 1998, said Don Lacquement of the Fairfax County Department of Public Works and Environmental Services (DPWES), presenting a "Dam 101" to the 50 community members gathered at Bonnie Brae Elementary School Thursday evening.
The study concluded an erosion failure might occur in the auxiliary spillway, for storms that exceed 18.5 inches in 24 hours, he said. According to the NRCS, a dam like the one at Lake Royal must be able to handle a probable maximum precipitation storm (PMP) of 27.5 inches of rainfall in six hours.
The Lake Royal dam has a principal spillway, a pipe that pierces the dam and drains excess water away from the site altogether through other pipes underground, said Lacquement. In case the volume of water is too great for the principal spillway, water would flow into the auxiliary (or emergency) spillway, a grassy ditch on the bank of the lake, instead of eroding and breaching the dam.
"[The auxiliary spillway] is a relief valve, if you will, for really big events," said Lacquement.
But that relief valve is the main problem with the Lake Royal dam. The principal spillway, which was built to last 100 years, is structurally safe. However, said Mathew Lyons of NRCS, the soil is not strong enough. If a massive storm were to hit, the water would soak into the ground, churn the soil, causing the dam to breach.
A PMP is statistically unlikely to occur in any given year, according to the NRCS. However, if the dam were to fail, water would flood the surrounding neighborhoods and nearby Guinea Road with very little warning.
"Virginia puts a really high value on the loss of life and external property damage that would occur if things were to fail," said Sheesley.
"It's not whether the dam is high enough, but the durability of the spillway material," said Lyons.
Diana Sheesley of the Department of Conservation Resources played a video of a dam failing in the White Oak Reservoir in Madison County, 63 miles away from Lake Royal. In the video, the water tore through what was the auxiliary spillway and eroded the surrounding land to the point that it looked like a muddy, small-scale Niagara Falls.
"Everyone has a stake in the project, but it all comes to public safety, that’s the bottom line," said Wade Biddix of NCRS. "Something has to be done."
THE DIVISION of Dam Safety and Floodplain Management must certify every dam in Virginia as safe, in accordance with the federal Small Watershed Rehabilitation Legislation enacted in 2000. Currently, the Lake Royal dam operates under a conditional certificate issued by the state to the Fairfax County Board of Supervisors. Once it is rehabilitated, it will be certified as safe, according to NRCS.
"Congress was wise to realize the importance of these dams to the safety of the country," said Biddix.
The Northern Virginia Conservation District, created by the federal government in the 1930s, will provide 65 percent of the federal cost-share for rehabilitation, as well as technical assistance and upgrades for 50 to 100 years, said Florence Naeve, chief of staff in the Office of the Braddock Supervisor.
Plans for dam repairs are still in the early planning stages, but three options now exist to strengthen the auxiliary spillway, said Carl Bouchard of DPWES. These include "armoring" the spillway or laying down material to prevent erosion, changing the cutoff walls, or a combination of these, he said.
Changing the cutoff walls is a technique used at Lake Braddock, but it is not always feasible for various reasons, said Bouchard.
In any case, said Bulova, more research must be conducted to determine the best method of repairing the dam. For this reason, Bulova’s office will create task forces of staff members, community members, and county officials to work on the rehabilitation project.
Tony Vellucci, vice president of the Kings Park Civic Association, Inc., is trying to do just that: get community members involved in a task force.
"Sharon [Bulova] mentioned having one or two people, I push for two or three people," said Vellucci. It is important for community members to be on the task force, he said.
"We are concerned about disruption on the lake, what there is going to be in terms of truck and materials and stuff on Pomeroy, Richardson, on the adjoining streets," said Vellucci. "We’d like to find a solution that creates the least disruption to the community."
Other citizens had concerns about parking. Clint Hall, a resident of Starboard Court since the dam was built, wondered where the construction vehicles would park. "That’s the only real entrance to the dam," said Hall. The number of residents’ cars in the court has multiplied, he said, making it difficult for traffic to go in and out. Bulova suggested clearing the area around current decanting basins to park equipment.
Decommissioning, or draining, the lake is an option but not a likely one, said Bulova. The lake is a part of the community, and the goal is to make sure it lasts, she said.
"People have gone there in quite bad moods, and come back rejuvenated," said Doreen Peiffer, a resident who attended the meeting with her family.
"We'll have a task force in the future so that we can make sure to further engage communities as plans come together," said Bulova.