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Huntley Meadows Park Wetland Restoration – Project Summary

In a Nutshell: The central wetland at Huntley Meadows Park has been slowly but steadily filling in with silt and debris, which reduces water depth and wildlife habitat. To restore the wetland to its 1980s condition, and provide long-term habitat for a community of locally rare plants and animals, the Fairfax County Park Authority and the Huntley Meadows Park community have decided to engage in wetland restoration. The 5 primary aspects of the project are: 1) an earthen berm to hold back water, 2) a water control structure to manage water levels, 3) expanding the wetland into the surrounding forest, 4) five deeper habitat pools to provide year-round wildlife habitat, 5) numerous brush shelters and logs to provide additional wildlife habitat. Construction started in April 2013 and was completed by March 2014. Total cost of design, permitting and construction was 3 million dollars. This was funded by park bonds and grants, and managed by Fairfax County Park Authority staff. Park staff and volunteers are now responsible for monitoring, management and maintenance of the restored wetland.

Aerial Wetland View

Expanded Summary: In the 1970s and 80s, Huntley’s central wetland was known for its regional significance as 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 3 feet) and consist of approximately 50% open water and 50% vegetated water –hence the term “hemi”. This particular hemi-marsh was created by beavers building their dam in a low, floodplain area that had been a forested wetland and old river oxbow for many years. 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.

Three factors have combined since the late ‘80s to slowly reduce the wetlands’ habitat and wildlife diversity: 1) deposition of silt and debris, 2) colonization and spread of aggressive plant species, 3) constantly changing beaver activity. Large amounts of silt have come from the surrounding suburban neighborhoods, as a result of concrete ditches carrying storm water, and from poorly regulated construction projects. Cattails and rice-cut grass are two of the primary aggressive plant species that have grown on all that deposited silt, and taken over areas that used to be open water. Lastly, beavers are nomadic and their habitats are cyclical by nature – they may raise water levels high enough to drown out most plant life, and they may also abandon their dams, allowing their wetlands to drain and dry out.

In order to ensure that Huntley Meadows Park has a functioning, healthy, diverse wetland that can support locally rare plants and animals on a consistent and long-term basis, management has become necessary to counteract the 3 factors listed above. This concept has been explored by Fairfax County Park Authority since 1992. Extensive research has been performed by three separate environmental engineering firms, as well as extensive monitoring done by park staff and volunteers. 20 public meetings have been held and the input from these meetings has been integral and central to the planning process. An additional 50+ public programs have been held to discuss the project with park visitors. The final result is that biodiversity, resource protection and environmental education are priorities for the Huntley community, and wetland restoration supports and realizes this list of 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 manage the wetland’s plant communities, which creates diverse habitat and attracts a unique community of wildlife species. Hemi-marshes need fluctuating water levels to maintain their unique plant communities; higher water levels in late fall thru early spring, lower water from mid spring thru early fall. Droughts and floods are equally important in maintaining a healthy hemi-marsh. Water levels must drop in the summer to expose mud to sunlight and oxygen, consolidate new silt, and allow new plants to sprout. Then they should rise in the winter to stop plants from taking over, flood the surrounding wood-edges and create deep, ice-free pools for aquatic life. This project and its management plan are centered around fluctuating water levels, and the habitat needs of hemi-marsh plants and wildlife.

Water Control System - Earthen Berm
The first part of our 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 therefor clear and visible. However, it will be earthen and vegetated, so it should eventually blend in to the wetland relatively well. We ask that visitors NOT walk across it, so that plants and soils can stabilize – thank you!

Water Control System – Slide Gates and Side Flow Outlet
The second part of our 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 will be 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.

Habitat Pools
Five habitat pools have been excavated approx. 3 feet below grade to provide deeper water habitat. This provides aquatic refuge during summer droughts and winter freezes, and 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 have been installed throughout the wetland to provide large, coarse, woody debris habitat for birds, reptiles, amphibians, crayfish, dragonflies, fish and aquatic mammals.

Expanded Wetland Footprint
This project will give park staff the ability to seasonally expand the central pool of the wetland to twice its current size; from 23.2 acres to 46.2 acres. It will also make it possible to seasonally expand the footprint of the wetland into the surrounding woodland, creating valuable flooded forest habitat.

Our Stories and Perspectives Blog:   Wetland Restoration Project Starts to Sing!

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