Difficult Run Tributary and Basins at the Government Center
A stream restoration and pond dredging project located near the Fairfax County Government Center building.
Yilia G. Vega-Claudio, Ian Vinson, Kenneth Trinh (Capital Facilities)
Scope of Work
The Difficult Run Tributary and Basins at Government Center project will consist of approximately 1,600 linear feet of stream restoration using Natural Channel Design (NCD) standards and dredging of two amenity ponds to improve stream health and water quality adjacent to the Fairfax County Government Center. The work includes the following: grading, excavation, fill, stream alignment, in-stream and log structure, and riparian corridor enhancement, native species landscaping, and trail rehabilitation.
Project Location
Goals & Objectives
Stream restorations are part of the County's efforts to satisfy state and federal clean water standards, colloquially known as an MS4 permit (Municipal Separate Storm Sewer System). These requirements are federally mandated under the Clean Water Act of 1972 and are designed to protect the Chesapeake Bay and local waters. Upon project completion, the County is required to protect and maintain the improvements to remain in compliance with MS4 requirements.
Goals and objectives of this project include minimizing soil erosion of existing stream banks, increasing biological uplift through channel realignment and installation of native plants, and improving water quality. The increase of water quality volume in the amenity ponds will enhance water quality storage.
Proposed Alignment
The project is all within Fairfax County Board of Supervisors' property and surrounded by adjacent pedestrian trails. The goal for relocating the stream is to mimic the conditions of a stable stream channel while keeping in mind the existing constraints of the site. The degree to which the channel can be moved is limited by the adjacent pedestrian trails, the quality of the forest and adjacent wetlands, and the necessary form and alignment of the stream bed and banks for a stable stream channel. In the process of the realignment, tree removal will be minimized based on a judicious assessment of need and the plant's overall health.
Tree Removal & Preservation
An extensive study to survey and inventory all existing trees over 12 inches in diameter at breast height was conducted on the project site. The inventory identified the tree species, health condition, and location of the trees within the proposed project area. Healthy trees will be closely monitored and evaluated throughout the design. Fairfax County intends to preserve as many healthy native trees on site as possible.
Trees that are noted to be removed are based on where either the proposed alignment or the temporary construction access road will be placed.
Functional Uplift
With NCD principles, the goal of the project is to restore the stream to a proper size and meander pattern so that it can support the stream's natural functions. Functions are the physical, chemical, and biological processes that occur in ecosystems. A corridor along the stream comprised of native trees and shrubs aids in stream function and provides many ecological benefits. In addition, a healthy plant layer aids in controlling and limiting the presence of non-native invasive plants and improves the likelihood of returning the stream corridor to its original condition and enticing animals to the area (aquatic and terrestrial).
Existing Conditions Map Tour
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Undercut bank looking downstream
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Looking downstream at the existing pond outlet channel
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Looking upstream at eroding outside bend
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Looking upstream at downed tree
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Looking downstream at pedestrian bridge with woody debris in channel
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Looking upstream at incised channel downstream of Monument Drive outfalls
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Looking upstream at incised channel
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Looking downstream at actively eroding bank
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Looking downstream at incised channel
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Looking upstream at incised channel
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Looking downstream at west pond in need of dredging
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Looking north at east pond in need of dredging
Limits of Disturbance, Proposed Improvements, and Trail Closures
Portions of the trails located behind the Fairfax County Government Center Building will be inaccessible to the public during construction. Staff will work with the contractor to phase the opening of the trails. Construction is anticipated to begin around August 2023 and last till about December 2024.
Pond Dredging and Fish Relocation
As part of the project, county staff will relocate fish from the two ponds at the Government Center, dredge and improve the ponds, and then restock the ponds with fish, to provide recreational and habitat improvements. During the time of construction, existing fish will be relocated to the Herrity Fountain Pond, which is located just upstream of the construction limits, at 12099 Government Center Parkway, Fairfax, VA.
Staff will work closely with the contractor to ensure that the sequencing of construction and the relocation of the fish are done safely; however, not all fish are guaranteed to be located safely.
Proposed Habitat & Vegetation Zones
Stream Channel
Streams provide many benefits to humans. Among them are drinking water, crop and garden irrigation supply, and water for industrial use. People often use streams for recreational activities such as swimming, fishing, and boating. These waterways also provide an aesthetic enhancement that many people enjoy on public and private property. Streams also provide important habitat for local plants and animals.
Streams provide an important ecosystem for many plants and animals, including fish, birds, salamanders, snails, frogs, and mammals. Different plants and animals have evolved to thrive in streams. Plants often have strong root systems that act as anchors, and long, flexible stems that can move with the current. These root systems support the plant and help anchor soil to control sediment erosion in the channel bed and on the neighboring banks. Aquatic fly larvae (think mayflies and caddis flies) nibble on leaves that have fallen into the water. Later, the flies become fish food. Mussels burrow into sediment on the stream’s floor to stay in place as they filter the water for food action that also helps keep water clean and clear. Many fish have streamlined shapes that help them stay in position in the water column and keep them from being washed away by strong currents. These fish provide a food source for stream corridor mammals and birds.
If streams are not badly eroded, during large precipitation events stream flow will rise to escape the channel and access the floodplain. Floodplains in good condition allow the water to spread out and slow down, decreasing channel erosion force. When water spreads out and slows channel erosion force decreases. Water in the floodplain also supports the plants and animals that live nearby. This water infiltrates the soil and recharges groundwater levels that help keep drinking water aquifers supplied. Adequate groundwater level also supports a healthy native vegetation corridor around the stream. Often, this is referred to as a riparian corridor.
Floodplain (Riparian) Forest
During heavy rainfall, areas adjacent to a stream may become periodically flooded. These zones are referred to as floodplain, or riparian, forests. A diverse array of vegetation can be found within this zone. Overstory and understory trees commonly found are species of oak, maple, birch, hazelnut, hollies, and spicebush. Sunny clearings within this zone are home to numerous wildflowers and grass species which provide food and shelter to songbirds and pollinators. Oftentimes snags, or standing dead trees, can be found within the riparian area, providing habitat for woodpeckers and other cavity-nesting birds.
Wetland
Except during a drought, nearly permanently flooded stream restoration zones consist of numerous grass species, as well as perennials and groundcovers. Wetland areas provide essential habitat to a wide variety of birds, insects, and sensitive amphibian species, including frogs and salamanders.
Upland Forest
Situated away from the effects of floodwater, these well-drained sites are typically characterized by more drought-tolerant plant species. Vegetation commonly found within the upland forest include tree and shrub species of oak, hickory, beech, hazelnut and dogwood, as well as many species of grasses, wildflowers, and ferns. These forests are typically drier and less densely vegetated than other plant zones associated with stream restoration, making them great areas for passive pedestrian recreation. Pedestrians can enjoy meandering walking trails with infinite possibilities for environmental interaction, including seasonal changes in plant aesthetics and wildlife observation.
Before and After: Piney Run at Lake Werowance Stream Restoration
For further information about stream restoration projects, and how they are developed prior to construction and after construction, see the photos of recently completed Piney Run at Lake Werowance Stream Restoration project, in Great Falls, VA.
Channel realignment and reconnection of channel to the floodplain.
Stabilized channel with a newly constructed pedestrian bridge.
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Contact Us
Please contact Kenneth Trinh at Kenneth.Trinh@fairfaxcounty.gov for more information.
Department of Public Works and Environmental Services