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Accotink Creek is the longest stream in Fairfax County,
stretching about 32 miles from the City of Fairfax to the Gunston
Cove. It begins with small feeder creeks and flows through Annandale
and North Springfield and then passes through Lake Accotink.
Like many streams in Fairfax County, Accotink Creek has
serious erosion. Development in the watershed has replaced
absorbent soil and vegetation with impervious (nonporous) surface
such as roofs, roads, and parking lots.
 Below
the dam of Lake Accotink is where the Virginia Department of
Forestry (VDOF) and the Northern Virginia Soil and Water Conservation
District (NVSWCD) demonstrated several stream bank stabilization
techniques to 40 participants at the end of an intensive three-day
workshop.
Jim McGlone is the assistant manager at Lake Accotink Park
through which a stretch of Accotink Creek flows. He offered
the site for the workshop because he is concerned about the
ecosystem of the stream as well as the Potomac River
into which the stream empties. He is particularly interested
in maintaining the stream for its fish habitat. The park stocks
the stream for trout fishing every spring and fall.
VDOF’s Judy Okay and NVSWCD’s
Asad Rouhi showed the group several bioengineering techniques
to protect the banks and improve habitat including biodegradable
logs and erosion control matting, shrubs and live stakes, and
cedar revetments. In addition, the group learned about structural
practices including a-jacks and rock cross vanes. (Click
here for definitions.)
The group donned its hip waders and jumped right in. Mike Blake
of the John Marshall Soil and Water Conservation District in
Fauquier County was impressed with what he saw and heard. “
We don’t do much with stream stabilization in Fauquier,
so these techniques are new to me.”
Joining the workshop team was the Fairfax County Department
of Public Works and Environmental Services, which operated
the heavy equipment needed to lift the larger rocks in the cross
vane.
An increasing number of local and county governments, homeowner
associations, and watershed groups are seeking the services
of the state forestry department and the conservation district
for hands-on stream stabilization training.
To learn more, contact Judy Okay at 703-324-1480 or via
e-mail. Contact Asad Rouhi at 703-324-1427 or via
e-mail .
- A-Jacks
- A-jacks are three two-foot long porous cement stakes
that fit together just like toy jacks. They are placed in
a row along a trench at the toe of a stream so that each a-jack
is interconnected with its neighbor. They add structural stability
to the lower bank.
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- Biolog
- Biologs are tightly bound cylinders of coconut (coir) fiber
held together by coir fiber netting. Generally, they come
in lengths of 10-20 feet and diameters of 10-12 inches. They
are installed at the toe of a bank. The material is tough,
flexible, and absorbent. Once installed, the biolog becomes
saturated with water, and vegetation can be planted directly
in it. By the time the log degrades in seven or eight years,
a root network of plants will have been established through
and behind it.
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- Tree Revetment
- A tree revetment consists of a row of trees that have been
cut, moved into place, and anchored against the lower part
of an eroding stream bank. Tree revetments protect the
banks until other vegetation can grow. Cedar trees commonly
are used for revetments.
-
 Live
Stake/Fascine- Live stakes are branches cut from live but dormant trees
and shrubs such as river birch, alder, red twig dogwood,
or willow. They are stuck into the banks through biodegradable
erosion control matting. The stakes will root and grow, holding
soil in place and providing wildlife habitat. Fascines are
tightly bound bundles of live stakes. Typically, fascines
are placed in a shallow trench along the stream bank parallel
to the stream.
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- Rock Cross Vane
- A rock cross vane is a rock structure which extends upstream
from both sides of the bank. Its purpose is to concentrate
the flow in the middle of the stream, thus narrowing the
flow path. As a result, it removes stress from the banks and
prevents erosion. A rock cross vane increases the flow depth
upstream from the structure, which improves fish habitat.
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