One of the healthiest watersheds in Fairfax County is set to get just a bit cleaner.
The Fairfax County Board of Supervisors adopted a management plan to address concerns along the Popes Head Creek Watershed, a 12,137 acre stretch of land that runs from Fairfax Station up to the southwest corner of Fairfax City.
"The base problem for the watershed is the excess of runoff due to impervious surfaces," said Paul Shirey, the county's project manager for the watershed.
As development has eaten up the open space in Fairfax County, water from rainstorms has a smaller and smaller amount of uncovered ground to be absorbed into, Shirey said. As rain comes down, the water runs off the hardened, non-porous surfaces, picking up pollutants and speed as it heads downhill and eventually into streams and ground water supplies.
"Increased runoff causes bank erosion problems in streams, which can lead to water quality issues," Shirey said.
The Environmental Protection Agency has found areas in Popes Head Creek with higher levels of several forms of bacteria, including fecal coliform, than are considered safe, he said.
The overall quality of the watershed is "at a tipping point," said Cliff Fairweather, a naturalist with the Audubon Naturalist Society and member of an advisory council for the watershed.
"There are some insects that we study to determine the quality of water that have smaller populations than we'd like to see," he said. "Then again, there's a lot of good fish diversity. We're doing work now to deal with the sources of runoff that can keep the stream at its current level and maybe make it a little better."
MOST OF THE STEPS involved in the management plan involve dealing with the bank erosion that results from increased runoff, which not only opens the creek to the possibility of changing courses but can cause silt and eventually reduce the amount of oxygen received by plants and animals that live in the water, Fairweather said.
"Luckily, most of the area along the watershed has been down zoned to 5-acre zoning because of the Occoquan River," he said. By reducing the amount of houses that can be built in any given area, the amount of impervious surface is reduced.
Most of the damage to the watershed comes from the headwater area, closest to Fairfax City, where much of the area is covered with non-porous material, Bartlett said.
"The water runs off faster and in a greater volume there," he said. "We try to retain the water on site as much as we can, but that's difficult to do."
Some parts of the watershed were designed to channel water away from houses by pipes, which caused localized flooding. Stormwater ponds, large, empty bowls designed to collect and retain water, became popular as a way to slow the runoff and create another location for the water to be naturally absorbed into the ground, Bartlett said.
Developers are currently looking into Low Impact Development (LID) practices to reduce the amount of runoff created by new construction, he said, by incorporating grass covered "green" roof technologies or by adding rain barrels to the bottom of down spouts, to collect water that could later be used to water plants.
To repair bank erosion, homeowners can help by allowing native trees, bushes and other deep-rooted plants to grow near the creek, Bartlett said. Homeowners should be cautioned not to use chemical fertilizers near stream beds, however, as the nutrients could wash into the stream and stimulate algae growth, which could suffocate plants and animals by using up oxygen in the water.
"This creek is a great ecosystem and it does support a lot of life," Fairweather said. "We can see a lot of animals in there, so it's not all doom and gloom. There's plenty of room to make some corrections and help keep it from deteriorating, which is what this plan sets out to do."
The plan adopted by the Board of Supervisors on Jan. 23 is a "work in progress" that allows the county's stormwater department to establish more specific goals and projects to keep the watershed healthy, Bartlett said.
"We've been able to inventory the various tributaries and parts of life in the stream and now that we have that, we'll be able to implement things to maintain the water quality," he said.
Part of the process will be to prioritize which projects are most needed to protect the species used to indicate water quality, Shirey added.
"At this point, the plan is very conceptual level of effort," he said. "All of the projects will have to be designed to implement what the plan mandates."