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Project Design: Buck
Engineering
Primary Contractor: Bell
Creek Farms
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CARRINGER/MITCHELL
(February - March 2004)
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Project
Background
The Carringer/Mitchell project site is along Little Brasstown Creek on
the properties of Jim and Janice Carringer and Dr. Brian Mitchell and
Dr. Nancy Troxler. It is situated upstream of the
Campbell project and downstream of the
Sheppard project in
the Little Brasstown Creek watershed; however, there is nearly a
mile-long reach immediately upstream for which restoration has been
designed, but not constructed.
The Carringer-Mitchell reach of Little Brasstown Creek has a drainage
area of 8.6 square miles and drains mostly pastureland and forest; there
is little impervious area. The reach was channelized historically and,
prior to construction, cattle had full access from the left bank of the
stream at this location. Approximately two-thirds of the right bank had
an excellent wooded riparian buffer as the stream is basically situated
at the base of the ridge. The left bank had severe to moderate erosion
and the riparian buffer was inadequate along approximately two-thirds of
the length. Bank sloughing was undermining the existing, inadequate
fence along the left bank and large pieces of land were being lost with
each significant rain event.
HRWC was somewhat limited in what could be accomplished at the
Carringer/Mitchell site for two reasons: (a) one adjacent landowner was
not willing to sign an easement and (b) Mr. Carringer did not want to
change the stream’s pattern because of the amount of pastureland he
would effectively lose. Therefore, the project was largely a stream bank
restoration project, although a few in-stream structures were installed
along the Carringer farm to improve the bed profile and provide bank
protection. Transplants, live stakes and brush layers were used to
provide bank stability. In the lower one-third of the project reach
along the Mitchell property, a combination of live stakes, fascines and
brush layers were used to stabilize the existing right bank of the
channel. Construction during the winter months of 2004 was critical to
the success of these bioengineering techniques.
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Before
Notice the
vertical bank and obvious erosion.
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After
Bank
was sloped and stream energy
directed to the center of the channel. |
Native tree species were planted along the Carringer farm and a portion
of the Mitchell property that did not have an adequate buffer. A new,
4-strand barbed wire fence was constructed according to NRCS standards
along the Carringer property to protect the newly planted buffer;
alternative watering for livestock is available on the pasture.
2008 Status
The entire 2042-foot restored reach was monitored in 2005,
2006 and 2007. The Carringer/Mitchell project is moderately stable,
with localized areas of bank erosion where repair work should be
considered. The restored reach contains eleven in-stream structures.
The majority of the structures are single arm rock vanes, which are
primarily serving as boulder toe protection for the banks, rather than
influencing the path of the water. Between 2005 and 2007, some
structures showed deterioration. Structures D, H, I, and K noticeably
deteriorated; structure K developed a serious piping problem. The
restored stream is currently classified as an E4 channel. The streambed
slope is 0.003 feet/foot, with an extremely low sinuosity of 1.01. The
median particle size is currently coarse gravel, which represents
significant coarsening since 2006.
The restored reach has two constructed riffles and other
stable riffles. Deep pools dominate the upper half of the restored
reach, while riffles and runs are generally predominant in the lower
half of the reach. The few pools that did exist in the lower half of
the reach became shallower or disappeared between 2005 and 2007. The
stream pattern was not changed as part of the restoration activities, so
the stream remains extremely straight. Localized areas of bank erosion
do exist, but are generally minor and not attributable to structure
failure.
Vegetation is well developed on the restored terrace, with
some problem areas at the fenced edge of the buffer and on the banks.
The buffer is fenced on the left bank. On the downstream right terrace,
a park-like planted area is mowed by landowners and some mowing damage
to planted trees has resulted. Air and water temperatures are being
moderated by the riparian buffer at Carringer/Mitchell.
Storm event samples
collected downstream of the restored site were lower in Total Suspended
Solids (TSS) than samples collected upstream by an average of 39%. None
of the eight sampling events showed an increase in TSS throughout the
project reach. Although the Carringer/Mitchell project is effectively
removing sediment from the system, levels of TSS on the upper end of the
project indicate a need for restoration in the W. Carringer/Tanney
reach.
The macroinvertebrate assessment yielded a bioclassification
of Good for all three years of monitoring. Between 2005 and 2007, the
number of EPT taxa and EPT abundance both decreased.
3-Year Study
Recommendations
In
addition to continuing to monitor this reach in subsequent years,
recommended actions include:
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Perform
emergency repair to
stop piping and bank erosion at left arm of Structure K
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Remove
exotic
invasives to prevent future problems
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Install
guards on trees in mowed area on Mitchell property to prevent further
damage
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