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Project Design: Buck
Engineering
Primary Contractor: Ownbey
Bulldozing
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GREASY CREEK
(June - July 2004)
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Project
Background
The Greasy Creek
project site is located less than half
a mile
upstream from the confluence of Greasy Creek and Brasstown Creek on
the properties of Joe Baumgartner and Judith Alvarado, and Jason and
Cathy Chambers. The restored reach is 1,472 linear feet long.
Nearly half of the
stream’s length in this reach was originally bordered on both sides
with exotic bamboo (Phyllostachys spp.). The stand of bamboo
covered approximately two acres and was 40-50 feet high. The plants
grow from branched rhizomes within the upper 18-36” of topsoil and
are not complex enough to hold the stream banks in place. Erosion
within the bamboo reach was moderate to severe and the stream was
unstable. In addition, very little light penetrated to the streambed
and aquatic habitat was severely degraded (no woody debris or root
masses).
Natural channel design principles were
applied to restore the channel’s dimension, pattern and profile to a
natural, stable form. The design for the middle portion (bamboo
reach) was to stabilize the existing unstable channel by changing
the dimension, pattern and profile. Root wads, cross vanes, and
constructed riffles were all used to stabilize the new channel and
improve aquatic habitat. Transplanted vegetation, live stakes and
brush layers were used to provide bank stability. Due to an adequate
riparian buffer and constrictions between the two roads on the lower
section, no pattern adjustment was made, but areas of existing
erosion were stabilized using root wads and brush layers.
Restoration was completed at Greasy Creek in summer 2004.
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Before
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After
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A 30ft-wide riparian buffer was established on the site. The
bamboo was removed from an area at least 15 feet from the top of
bank along the entire project reach. It was isolated using a thick
rubber barrier installed in the ground three feet deep and at an
angle to force new bamboo shoots to the surface before reaching the
riparian buffer area. These shoots will be cut and/or killed with
mowing and herbicide treatments by the landowners as part of the
Coalition’s agreement for project maintenance.
In fall 2004,
prior to planting of the riparian buffer, a series of storms passed
through the area, including the remnants of Hurricane Ivan. Two
sections of the newly constructed channel failed and had to be
repaired by HRWC using contingency funds. There have been no
problems since, most likely because of the establishment and
protection of good woody buffer vegetation.
2008 Status
The 3-year old
Greasy Creek restoration project is very stable, with no notable
bank erosion. Between 2005 and 2007, most structures showed little
or no change. The restored stream reach currently shows
characteristics of both a C4 and an E4 channel. The streambed slope
is 0.015 feet/foot, with a sinuosity of 1.24. Between 2005 and
2007, the streambed material consistently became coarser, with a
current median particle size representing coarse gravel.
The restored
reach has several riffle/run segments and a few deep pools. The
pools are located in the expected planform locations beneath cross
vanes and in meander bends. Riffles generally dominate the straight
reaches, but a few riffles do appear to be migrating into meander
bends. As a result of a very tight meander bend (created to save
one large remnant hardwood tree), there is an instance of very high
shear stress within the reach. However, due to well-vegetated banks
and good floodplain access, bank erosion is essentially
non-existent.
New woody
plantings contribute high diversity and density; however, mowing of
the buffer is suppressing understory development. As early
successional species colonize both wetland and drier terraces,
Greasy Creek ranks among the highest herbaceous diversity of the
monitored projects.
Downstream Total
Suspended Solids samples were all slightly lower than those
collected upstream, with an average reduction of 7% over the
monitoring period. These results suggest that restoration has
resulted in lower erosion rates, and that the reach is effectively
depositing its sediment load. This was a major goal of the
restoration effort.
Although Greasy
Creek is too small to assign a bioclassification, the number of EPT
taxa remained nearly constant, while the EPT abundance decreased
slightly each year, between 2005 and 2007.
3-Year Study
Recommendations
Recommended actions
at Greasy Creek include:
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Yearly removal of two
exotic invasives (bamboo and privet)
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Continue
to monitor in
subsequent years, with particular attention given to the vicinity of
Structure B and two 90-degree meander bends
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