Case Study - Huntley Meadows Wetland Restoration

Huntley Meadows Wetland Restoration Fairfax County, Virginia LAR7500 Precedent Study Yangqianqian Hu

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Huntley Meadows Wetland Restoration

THE HUNTLEY MEADOWS PARK WETLAND RESTORATION

Project Team: Wetland Studies and Solutions, Inc.* Client: Fairfax County Park Authority Location: Fairfax, VA Completion: 2014

*Wetland Studies and Solutions, Inc. is the leading natural and cultural resources consultant in the Mid-Atlantic region. Our engineers, scientists, regulatory specialists, permit compliance specialists, arborists, archeologists, architectural historians, ecosystem & restoration specialists, surveyors, and geographic information specialists assist both the public and private sectors with the permitting process and create innovative solutions to water quality issues.

Huntley Meadows Wetland Restoration 3 Image credit: https://www.fairfaxcounty.gov/parks/huntley-meadows/wetland-restoration

THE HUNTLEY MEADOWS PARK WETLAND RESTORATION

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.

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Huntley Meadows Wetland Restoration

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.

Huntley Meadows Wetland Restoration 5 Image credit: https://www.fairfaxcounty.gov/parks/huntley-meadows/wetland-restoration

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Huntley Meadows Wetland Restoration

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Huntley Meadows Wetland Restoration

HUNTLEY MEADOWS WETLAND

1971 and 1984 aerial views of Huntley Meadows

1994 and 2004 aerial views of Huntley Meadows Flooded forested wetland

Hemi-marsh

Lake marsh

Dry marsh/wet meadow

The park was established in 1975 and covers approximately 1,500 acres. The central wetland area is one of the largest non-tidal wetlands of its kind in Northern Virginia. Since the late 70s, the central wetland has transitioned from a flooded forested wetland, into a hemi-marsh* and then to a lake marsh due to beaver damming activities.

*A hemi-marsh is a type of wetland that typically found in areas where water levels are too deep to support extensive woody vegetation. Hemi-marshes are characterized by a mix of emergent vegetation and submersed plant life associated with shallow open water environments.

Huntley Meadows Wetland Restoration

However, as a result of recent consecutive droughts, siltation from upstream development north of the park, beaver activities, herbivorous feeding habits of Canada geese, and natural succession, the wetland has deteriorated to a dry marsh/wet meadow with uniform shallow water levels. These conditions promoted the development of large stands of invasive species such as broad-leaved cattail (Typha latifolia L.) within the park, reducing habitat, and thus wildlife diversity.

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The project’s goal is to increase biodiversity and ecological function (e.g. water quality) within Huntley Meadows Park by restoring the central wetland area to a hemi-marsh system, with presumed higher levels of biodiversity and ecological function. The hemi-marsh will contain roughly 50 percent open water and 50 percent vegetated wetland in the winter, will dry out in the summer, will have more woody shrubs than currently present, and will have fewer non-desirable herbaceous plants, such as cattails. The restored wetland system will provide annual forage and a diversity of habitat quality for target plant and animal species that were once observed at the wetland and will prevent the dominance of invasive plant species.

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Huntley Meadows Wetland Restoration

Flooded forested wetland

Hemi-marsh

Lake marsh

Dry marsh/wet meadow

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.

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.

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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.

Huntley Meadows Wetland Restoration

Habitat Pools 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.

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Huntley Meadows Wetland Restoration

Huntley Meadows Wetland Restoration

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Huntley Meadows Wetland Restoration

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Huntley Meadows Wetland Restoration

WATER CONTROL STRUCTURE

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.

Huntley Meadows Wetland Restoration

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Huntley Meadows Wetland Restoration

PRE-CONSTRUCTION VEGETATION MAP

POST-CONSTRUCTION VEGETATION MAP

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BRUSH SHELTERS AND LOAFING LOGS

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HABITAT ENHANCEMENT

Five years down the line, the wetland is showing noteworthy improvements, including more biodiversity and healthy ecological function. The restoration increased the size and depth of the wetland. Berms were installed, and management now can hold back or release wetland waters. Since the project’s completion, Huntley Meadows staff have been actively managing the wetland.

Huntley Meadows Wetland Restoration

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Summary map of Huntley Meadows Park wetland restoration plan (Wetland Studies and Solutions Inc., 2013).

Conclusion This design deals with a wetland system and the embedded plant/ animal systems in the wetland. The wetland was undergoing a natural succession to a dry marsh/wet meadow due to the upstream siltation development, droughts and animal feeding. Prior to restoration, the wetland area was dominated by large, monotypic stands of invasive species as a result of uniform shallow water levels, which greatly reduced the diversity of wildlife habitat and degraded the ecological function. The design still allow succession to occur but it slows the succession and tries to manage the rate of succession in the wetland.

The project’s goal is to increase biodiversity and ecological function (e.g. water quality) within Huntley Meadows Park by restoring the central wetland area to a hemi-marsh system, with presumed higher levels of biodiversity and ecological function. The key aesthetic goals of this project is to maintain the central wetland as part of the recreational system of the park.

The key ecological concepts that inform the design is the fluctuating water level created by a set of structures and enhancing habitat for non-human agencies by using habitat pools and diverse plant species.

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. By managing the water level, this design prevents water levels that are too high or too low, which might lead to different plant communities and then alter the whole landscape.

The projects also introduce more diverse plant communities to the site, including reduce the area that was occupied by invasive species and grow floating aquatic plants to increase the metabolic processes of the wetland systems.

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This project is situated in the middle of an urban park, which works as a patch to provide habitat within the landscape matrix.