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Project Design: Buck
Engineering
Primary Contractor: Robert Truett
Grading
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SHEPPARD
(January - March 2003)
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Project
Background
The Sheppard reach of Little Brasstown
Creek has a drainage area of 6.25 square miles and is located
immediately below the Mason/Stalcup project reach. Land uses are mainly
agricultural and forested land. The Sheppard reach was severely
degraded by stream bank erosion and channel instability caused by past
channel modifications, cattle access, and inadequate riparian buffers.
Existing vegetation consisted of mainly grasses in open pasture and
cattle had full access to the stream along the majority of the
4,000-foot reach. The goals of the project were to improve water
quality and aquatic habitat, stream stability, and riparian and
floodplain functionality.
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Before
Channel
instability and bank erosion on the Sheppard farm was caused
by historic channelization, a lack of riparian vegetation
and cattle access.
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After
A
completely new channel was constructed
on the other side of
the tree at this location.
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After
The new
channel was designed with a more stable pattern,
based on a
similar stream that is relatively undisturbed.
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Riparian Buffer
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Early in 2003, natural channel design principles were
applied to restore the channel’s dimension, pattern and profile to a
natural, stable form. The design for the upper 2/3 of the reach was to
stabilize the existing unstable E4 channel by changing the dimension,
pattern and profile. Root wads, cross vanes, j-hooks, log 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 a good existing
riparian buffer on the left bank of the lower reach, no pattern
adjustment was made, but areas of existing erosion were stabilized using
root wads and brush layers. Three weeks after construction was
complete, the Sheppard project survived a major flood event (10-year
reoccurrence interval)! Only minor repairs were required.
Native trees and shrubs were planted with the 30-foot
riparian buffer area along both sides of the stream. A new 4-strand
barbed wire fence along the entire project reach protects the buffer
area as livestock graze on the farm.
2008 Status
More than half (2539 feet) of the Sheppard stream restoration project
was monitored in 2005, 2006 and 2007. The monitored reach is moderately
stable with some areas of concern and a few areas where repair work
should be considered. The restored reach contains 21 rock structures
that are holding grade and providing stream bank protection. Most
structures showed little or no change and are functioning as intended.
A few appear to have contributed to localized stream bank erosion;
structures A, B, and K noticeably deteriorated between 2005 and 2007.
The restored stream is currently classified as a C4 channel. The
streambed slope is 0.004 feet/foot, with a sinuosity of 1.47. Between
2005 and 2007, the streambed material has become coarser, with a current
median particle size representing coarse gravel.
The restored reach has mostly stable riffles and pools located in the
expected planform locations. The locations of riffles and pools
generally did not change between 2005 and 2007. Cross-sectional
dimensions remained similar between 2005 and 2007. Stream bank erosion
is occurring mostly along the outside of meander bends with high
near-bank shear stress and failing structures. However, most of the
in-stream structures are functioning to reduce near-bank stress and hold
grade. In two locations where structures are not functioning properly,
stream bank erosion indicates a relatively urgent need for repair to
restore stability and prevent further erosion.
Planted vegetation in the riparian buffer along the new
channel at Sheppard is generally thriving. Air and water temperatures
are both being moderated by the dense buffer. As shown on Figure 3
(page 15) of Section 3, peak water temperatures downstream of the
restored reach were consistently lower than measured upstream
temperatures suggesting that riparian vegetation is having the desired
cooling effect on the stream. There are, however, some bare banks
inside the planted buffer need attention.
Sheppard also had consistently lower Total Suspended Solids
concentrations in downstream water samples. The average reduction there
was 41% and the only one of seven events to show an increase, only went
up by 1%. Like Mason/Stalcup upstream, this project is effectively
managing a fairly heavy sediment load and would benefit from reduction
of TSS from upstream sources.
The benthic macroinvertebrate assessment yielded a
bioclassification of Good during each of the monitoring years. However,
between 2005 and 2007, the number of EPT taxa and EPT abundance slightly
decreased.
3-Year Study
Recommendations
In
addition to continuing to monitor this reach in subsequent years,
recommended actions include:
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Install
live stakes on bare
banks and consider early removal of invasives to prevent later
large-scale problems
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Evaluate
potential implications of a beaverdam at Structure R
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Consider
bank and structure repair in the vicinity of Structure C
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