In a Nutshell: Over the years, the central wetland at Huntley Meadows Park slowly filled with silt and debris. That reduced water depth and wildlife habitat. To restore the wetland to its 1980s condition and to provide long-term habitat for a community of locally rare plants and animals, the Fairfax County Park Authority and the Huntley Meadows Park community decided to take on a massive restoration. There were five primary aspects to the project:
• Create an earthen berm to hold back water
• Build a water control structure to manage water levels
• Expand the wetland into the surrounding forest
• Establish five deeper habitat pools to provide year-round wildlife habitat
• Create numerous brush shelters and logs to provide additional wildlife habitat.
Construction started in April 2013 and was completed in March 2014. Total cost of design, permitting and construction was 3 million dollars. Funds came from park bonds and grants and were managed by Fairfax County Park Authority staff. Park staff and volunteers monitor, manage and maintain the restored wetland.
Expanded Summary: In the 1970s and 80s, Huntley’s central wetland was one of the most productive and diverse non-tidal wetlands in the mid-Atlantic area. Specifically, it was a hemi (also called emergent) marsh. Hemi-marshes are shallow wetlands, usually less than three feet, and consist of approximately 50% open water and 50% vegetated water – hence the term “hemi”. Beavers created Huntley’s hemi-marsh by building their dam in a low, Potomac River floodplain that had been a forested wetland and old river oxbow. The habitat they created attracted many locally, even regionally, rare wildlife species, including American Bittern, Least Bittern, Yellow-crowned Night Heron, King Rail, Pied-billed Grebe, Common Moorhen and a long list of reptiles and amphibians.
Starting in the late 1980s, three events combined to slowly reduce the wetlands’ habitat and wildlife diversity:
• Deposits of silt and debris
• Colonization and spread of aggressive plant species
• Constantly changing beaver activity.
Large amounts of silt arrived from surrounding suburban neighborhoods because of concrete ditches carrying storm water and poorly regulated construction projects. Cattails and rice-cut grass were two of the primary aggressive plant species. They grew on the deposited silt and took over areas that had been open water. Lastly, the beavers moved. Beavers are nomadic, and their habitats are cyclical by nature. Their dams may raise water levels high enough to drown out most plant life, and beavers sometimes abandon their dams, allowing their wetlands to drain and dry.
To ensure that Huntley Meadows Park had a functioning, healthy, diverse wetland, management became necessary. The Park Authority started exploring the idea of actively managing the wetlands in 1992. There was extensive research by three separate environmental engineering firms and extensive monitoring by park staff and volunteers. There were 20 public meetings, and the input from those meetings was central to the restoration planning process. More than 50 public programs were held to discuss the project with park visitors. Those meetings revealed that biodiversity, resource protection and environmental education were priorities for the Huntley community. A wetland restoration would fulfill those priorities.
How it Works
Fluctuating Water Levels
The best way to manage a hemi-marsh for long-term biodiversity is to manage the water levels. Water levels determine a wetland’s plant communities, which then create diverse habitat and attract specific communities of wildlife. Hemi-marshes need fluctuating water levels to maintain their unique plant communities -- higher water levels in late fall through early spring, lower water from mid-spring thru early fall. Droughts and floods are also important. Water levels must drop in the summer to expose mud to sunlight and oxygen, to consolidate new silt, and to allow new plants to sprout. Water levels must rise in the winter. That prevents plants from taking over and floods the surrounding wood edges to create deep, ice-free pools for aquatic life. The Huntley wetlands restoration is centered around fluctuating water levels.
Water Control System - Earthen Berm
The first part of the water control system is a low, earthen berm with a vinyl sheet piling center. The berm is just a few feet high, 600 feet long, gradually sloped and vegetated with native plants. It is straight, and therefore visible. However, it is earthen and vegetated, so it should eventually blend into the wetland relatively well. We ask that visitors not walk across it so that plants and soils can stabilize.
Water Control System – Slide Gates and Side Flow Outlet
The second part of the water control system is a concrete box with plastic pipes and metal slide gates that allow park staff to manipulate the wetland’s water levels. The box and pipes are underwater (and under a new observation platform) so they are hidden from view during all but severe droughts. A natural surface side flow outlet leads out of the pipes, allowing the structure to vent water back into Barnyard Run behind and below the earthen berm.
Five habitat pools about three feet below grade provide deeper water habitat. These provide aquatic refuge during summer droughts and winter freezes. They also provide diving habitat for wildlife such as Pied-billed Grebes, Hooded Mergansers and otters as well as fish and crayfish.
Brush Shelters and Loafing Logs
Numerous wildlife brush shelters and large loafing/sunning logs in the wetland provide large, coarse, woody debris habitat for birds, reptiles, amphibians, crayfish, dragonflies, fish and aquatic mammals.
Expanded Wetland Footprint
Park staff seasonally expands the central pool of the wetland to twice its size from 23.2 acres to 46.2 acres. The system also makes it possible to seasonally expand the wetland footprint into the surrounding woodland, creating valuable flooded forest habitat.