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Soft Engineering of Shorelines Based on a Binational Conference Sponsored by the Greater Detroit American Heritage River Initiative and Partners |
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Chapter 10 Bioengineering for Erosion Control and Environmental Improvements, Carson River, Nevada (Hollis Allen, Craig J. Fischenich, and Rebecca Seal, U.S. Army Engineer Research and Development Center, Waterways Experiment Station) Introduction This case study is an excerpt from
a conference proceeding (Piper et al. 2000) and Power Point presentation
prepared by Hollis Allen and Craig Fischenich of the US Army Engineer
Waterways Experiment Station. In January 1997, the Carson River watershed
experienced a 100-year flood event of approximately 23,000 cfs, leaving
many reaches of the Carson River in need of restoration. Landowner property
as well as the native overstory cottonwoods and willows were threatened
by the erosion. A restoration workshop was held to determine the best
means for repairing the damage and conveying the long-term success and
benefits of bioengineering treatments for controlling erosion in an
environmentally compatible manner. The bioengineering workshop/restoration
project was completed November 2-4, 1998 in Carson City, Nevada. The
river restoration project was implemented on a portion of the Carson
River within Dayton Valley, Lyon County, Nevada (Figure 31). With the
involvement of the local coordinated resource management group, landowners,
local, state, and federal agencies worked together to provide technical
assistance, funding, and permitting. The coordinated efforts of these
various groups made this bioengineering workshop/restoration project
a success.
Key features of the site prior to restoration include:
A reconnaissance of the river restoration
site, by resource professionals involved in the bioengineering workshop
and river restoration project, indicated that bioengineering treatments
alone would probably not be effective. This determination was based
on existing soil conditions, lack of existing vegetation, and the potential
for long durations of high streamflows resulting from annual spring
runoff conditions. Streamflows on the Carson River, during the spring
runoff of 1999, peaked at approximately 4,000 cfs. Hard structures that consisted of stream spurs or barbs, rock refusal trenches, rock toe protection, and a peaked stone dike were determined to be the best options. After an analysis of project site and river velocities, five barbs were designed to cover the entire bendway. In addition to the two rock refusal trenches and the rock toe protection, a peaked stone dike was added to the lower third of the bendway where there was a change in landowners and where the main force of the current had eroded the streambank back into a horse corral. This area also had several large willows and cottonwoods that would have to be removed if the bank was sloped back. The peaked stone dike would allow the bank to be built out without sloping. More details on the design and layout of the hard structures can be found in the reference Piper et al. (2000). Bioengineering Treatments Installed
Upon completion of bank sloping and
installation of the hard structures, a number of bioengineering treatments
were installed to demonstrate several techniques that can be used for
streambank stabilization, restoration, and management (Allen and Leech
1997; Hoag and Bentrup 1998). A brush mattress was installed along 36
linear feet of streambank, between the first rock refusal trench and
the first stream barb (Figure 32). This brush mattress was selected
to demonstrate a specific treatment that could be installed to reduce
accelerated erosion to an existing eroding streambank and to establish
plant growth along the streambank.
Willow clumps with a juniper tree revetment
and seeding, and erosion control fabric, were installed along 98 linear
feet of streambank between the second stream barb and the third stream
barb (Figure 33). Willow clumps are live willows that have been transplanted
with the root ball intact. Within this area, a total of 40 willow clumps
were transplanted into two rows behind the juniper tree revetment. This
treatment was selected to establish willow plant growth to reduce erosion,
encourage deposition of suspended sediment, and improve wildlife habitat
associated with the immediate streambank. A juniper tree revetment was
installed at the toe of the streambank, in front of the willow clumps,
to protect the willow clumps and to assist with trapping suspended sediments
and encourage additional deposition of soil during high flow events.
The top portion of the streambank was seeded and covered with an erosion
control blanket. A brush trench was installed along
49 linear feet of the streambank, with rock toe protection, between
the third stream barb and the second rock refusal trench (Figure 34).
The brush trench was installed as another bioengineering treatment to
stabilize the streambank. This treatment requires adequate toe protection
be installed to ensure that the brush trench does not erode during high
flow events. This treatment, once established, provides streambank stability,
filters runoff (from the thick willow root matrix), and provides cover
for wildlife.
Brush layering and seeding, with an erosion control blanket, was the final bioengineering treatment installed along a total of 196 linear feet of the streambank. This treatment was installed along with the peaked stone dike structure located between the second rock refusal trench and the fifth stream barb. The brush layering was selected to assist with stabilizing the streambank, provide shade to the river, and provide food for the fishery. This treatment was installed on the inside slope of the peaked stone dike. Topsoil was placed on the inside slope of the peaked stone dike to provide good soil contact with the willow brush layer. The willow brush layer was placed on this inside slope of the dike with the tops of the willows projecting out over the water and covering the top of the peaked stone dike. Upon completion, a willow brush layer fill material was placed over the stems of the willow brush layering and a 3:1 slope was created to tie back into the top of the existing slope. This fill material was then seeded and covered with erosion control fabric. Regulatory Considerations The consortium of agencies participating in this project included the US Army Corps of Engineers Regulatory Office out of Reno, Nevada (part of the Sacramento District Office of the US Army Corps of Engineers). They were working under a Section 404 Permit of the Clean Water Act that the Corps was overseeing. Project Costs The total project costs for this bioengineering streambank stabilization and restoration project was $61,000 ($101/lineal foot). Cash expenses for this project were $44,762 ($75/lineal foot). Cash expenses were construction and materials costs. In-kind expenses contributed to this project were $16,184 ($27/lineal foot). In-kind expenses were plant materials, labor, and equipment. In-kind expenses made up 26.5% of the total costs of this project. The neighboring landowners and local river management group provided the in-kind services. Funding and Implementation Partners The following is a list of the local, state, and
federal agencies who sponsored and collaborated together to make this
a successful project: Carson Truckee Water Conservancy District; Post Project Monitoring Vegetative monitoring along 9 fixed transects was
used to help evaluate the success of the bioengineering treatments installed.
From the data collected, there was an average of 74% cover on all treatments,
with the highest first year vegetative cover established on the erosion
control blankets, vertical willow bundles above the juniper tree revetment,
and the willow brush trench treatment. The highest number of re-sprouts
of willows occurred on the vertical willow bundles above the juniper
tree revetment, followed by the willow brush trench, and the willow
brush layering above the peaked stone dike located between the second
rock refusal trench and the fourth stream barb. Figure 35 shows all
5 barbs and bioengineering treatments looking upstream.
The willow clump bioengineering treatment presently
has 14 out of 40 (35%) of the willow clumps regenerating, while the
other 26 (64%) willow clumps are buried by the large amounts of deposited
sediment within the treatment area. Six vegetative line intercept cross-section composition
transects have been established and will be part of the long term monitoring
program for this bioengineering project. No data comparison is available
at this time. Topographical surveys of the site done before construction
and 9 months following construction have revealed that 430 cubic yards
of sediment were deposited between the first stream barb and the fifth
stream barb along the bendway. A total of 6 fixed cross-sections have been established to monitor the change in channel morphology. The 6 cross-sections are located in conjunction with each of the bioengineering treatments installed. The present cross-sectional information illustrates the successful movement of the low flow channel (thalwag) away from the bendway. This suggests that the stream barbs have deflected the higher stream flow velocities away from the bendway causing the low flow channel (thalwag) to migrate to the ends of the stream barbs as designed. This in turn can also be linked to the amount of deposition that has occurred between the stream barbs as a result of the calm water areas developed between the stream barbs, which have allowed the river to deposit sediment within these areas by design. Benefits of Project The benefits accrued by this project are manifest
both in the achievement of changes in the physical characteristics of
the river and in the successful collaboration of the multiple stakeholders
that actively supported the effort. The series of barbs and the peaked
stone dike successfully moved the thalwag away from the cutbank and
induced sediment deposition where it was needed. The bioengineering
treatments in between the barbs are gradually covering areas with vegetation
that have the potential to improve fishery and wildlife habitat in the
stream. The treatments will serve as good examples of stream stabilization
techniques for future projects. The US Army Corps of Engineers recognizes the relevance of bioengineering practices for a number of important reasons. Bioengineering is a "greener approach" to erosion control that is being explored by many agencies, including environmental and non-government organizations, for enhancing new projects. It is also useful for preserving cultural resources without hard armor that may be less aesthetically pleasing or present barriers to access. Also, bioengineering methods are often more cost-effective than traditional approaches. Advise for Overcoming Obstacles When Using Soft Engineering
Practices When addressing social obstacles for the use of
bioengineering, it is useful to look at what has been successfully done
elsewhere, such as in Germany, Austria, and in various parts of the
United States. It is important to emphasize that bioengineering, when
properly designed and employed, can provide good habitat features, improve
water quality, and help to control erosion. The Carson River Case Study
is a good example of employing both "hard" and "soft" methodologies
to safely achieve erosion protection goals, while also enhancing the
environmental quality of the same area. Additional information about the successes and failures of bioengineering in this country will be available through the US Army Corps of Engineers web site in the future.
References Allen, H.H. and J.R. Leech. 1997. Bioengineering for Streambank Erosion Control. Technical Report EL-97-8, US Army Engineer Waterways Experiment Station, Vicksburg, Mississippi. Hoag, J.C. And G. Bentrup. 1998. The Practical Streambank Bioengineering Guide - User's Guide for Natural Streambank Stabilization Techniques in the Arid and Semi-arid Great Basin and Intermountain West. Interagency Riparian/Wetland Plant Development Project, USDA-Natural Resources Conservation Service, Plant Materials Center, Aberdeen, Idaho. Piper, K.L., J.C. Hoag, H. Allen, G. Durham, and C. Fischenich. 2000. Bioengineering as a Tool for Restoring Ecological Integrity to the Carson River. Conference 31, International Erosion Control Association, Palm Springs, California. Note: Technical input was also provided by: Web Sites http://www.ieca.org
Contact Persons Craig J. Fischenich Hollis H. Allen US Army Engineer Research and Development Center |
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Last updated:
July 9, 2008
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