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Project Design: ARCADIS G&M
Primary Contractor: Ownbey
Bulldozing
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WARNE
(February - April 2001)
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Project
Background
The site is located
along a 4,500-foot reach of Brasstown Creek and flows through eight
properties in the community of Warne, NC. The project is the most
upstream of all projects along Brasstown Creek and is only about one
mile from the NC-GA state line. It is also one of the oldest projects,
having been constructed early in 2001.
Due to past farming
practices in the community, including livestock access to the creek and
inadequate riparian vegetation along its banks, this section of
Brasstown Creek exhibited severely eroding stream banks prior to
restoration. Soil loss through erosion for this reach of the creek was
estimated to be at least 1,300 tons per year. The goals for restoration
work were to improve water quality and aquatic habitat by reducing bank
erosion and sedimentation, improve stream stability and riparian and
floodplain functionality.
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Before |
After |
This project resulted
in a partnership with eight landowners along the creek. Restoration
consisted of installing root wads and constructing rock vanes, j-hook
vanes, and cross vanes. Livestock exclusion fencing was installed and
a 50-foot riparian buffer was reestablished using native trees and
shrubs.
2008 Status
Approximately 2,200-linear foot reach of this project was monitored in
2005, 2006 and 2007. This portion of the Warne stream restoration
project is stable, with a few areas of concern. Thirteen structures
provide bank protection and grade control within the monitored reach.
Several single arm rock vanes have experienced some deterioration,
typified by boulder movement and localized bank erosion; however, the
three cross vanes continue to successfully hold grade after nearly seven
years. The restored stream reach is currently classified as a C4
channel. The streambed slope is 0.003 feet/foot, with a sinuosity of
1.30. Between 2005 and 2007, the streambed material became slightly
finer.
The
restored reach contains several riffles and pools. Riffles are
typically associated with the cross vanes and j-hook vanes, while pools
are present in the expected locations at meander bends. Between 2005
and 2007, the pools generally became deeper and moved toward the outside
of the meander bends. Riffles remained in the same planform locations
while generally showing slight aggradation. Some stream bank erosion is
occurring sporadically throughout the channel, typically in areas with
structural failures and poor vegetative growth.
Few
areas were disturbed by construction, so remnant trees are common and
planted vegetation is localized. Vegetation is generally thick and the
banks are stable. Understory vegetation is dominated by blackberry and
dewberry (Rubus spp.), privet (Ligustrum sinense), river
cane (Arundinaria gigantea) and early successional species.
Based on water temperature data collected during the monitoring period,
the riparian buffer appears to be moderating peak temperatures.
Even
with a large sediment load coming into the reach from unrestored
portions of the watershed in Georgia, at Warne, four out of six sampling
events resulted in decreases in Total Suspended Solids between the
upstream and downstream ends of the project. An average decrease in TSS
of 16% was recorded over the monitoring period.
In 2007, the
macroinvertebrate assessment yielded a bioclassification of Good, the
same as in 2006. Between 2005 and 2007, EPT taxa richness and abundance
both saw a net increase. Macroinvertebrate bioclassifications are
comparable at Brasstown Creek sites further downstream of the Warne
project
3-Year Study
Recommendations
In
addition to continuing to monitor this reach in subsequent years,
recommended actions include:
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Remove
privet and replace with native plantings to increase habitat quality
and prevent spread of exotics to nearby landowners
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Encourage
vegetation growth on bare banks and at the areas of localized stream
bank erosion, typically near the rock structures
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Closely
monitor those areas with high near-bank shear stress; specifically
at three locations between stations 13+50 and 14+40, 17+49 and
18+15, and 1+24 and 6+20
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Evaluate
the potential implications of a beaver dam at Structure G
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