PROJC02275 ‎(2)‎

• Contract/PO #: C150166
• Contractor Name: East Fork Mutual Irrigation Company
• Contract Type: Loan
• Water District: 50
• County: Grand
• Loan Projects - Doc Type: Feasibility Study

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Geotechnical 1 Environmental Engineering • Materials Testing
May 16, 2003
East Fork Mutual Ditch Company
c% Kent Whitmer
Box 38
Hot Sulphur Springs, CO 80451
Job Number: 03-5547
Subject: Additional Slope Protection
Recommendations, East Fork Troublesome Ditch -
Elk Fork Ranch, Grand County, Colorado.
~ Gentlemen:
As requested, NWCC, Inc. (Northwest Colorado Consultants, Inc.) has prepared this report to outline
alternative methods for protecting the slopes that will be disturbed during the stabilization/remediation of
the slope failure that occurred beneath a section of the East Fork Troublesome Ditch. It should be noted
that our firm previously prepared a report that outlined our observations of the subject slide and provided
recommendations for stabilizing the slide. The report was prepared under this job number and dated May
7, 2003.
It is our understanding that the ditch owners have elected to construct a pipeline in the present ditch
alignment, approximately 1000 feet in length, and then remove all of the failed materials and existing fill
materials from the area of the slope failure to form a more stable slope configuration. However, it does not
appear that it will be feasible to armor the completed cut slopes with boulders, as recommended in our
original report. Therefore, we have provided alternative methods for protecting the slopes after the
construction has been completed.
There are a large number of erosion control products that should work satisfactorily if they are properly
installed and maintained after the slopes have been seeded. Based on the assumed final slope configuration
of approximately 1 (Horizontal) : 1 (Vertical) to 1 '/~ (Horizontal) : 1 (Vertical), the soil conditions and
r climate at the site, we recommend that at a minimum an erosion control blanket that is reinforced on both
sides with a heary duty, extruded plastic mesh be used to cover the disturbed slopes. These erosion
blankets can be either be filled with Aspen wood fibers, such as the Curlex III blankets produced by
Excelsior, which have a limited functional longevity of 18 to 24 months, or they can be filled with a
synthetic fibers, such as CONTECH's TRM C35 blankets, which are permanent reinforcement mats. Due
to the amount of disturbance that occurs in this area as a result of the elk and deer running up and down, as
well as across the slopes, the client should be aware that these types of mats may not hold up to the
disturbance and damage caused by the wildlife and a considerable amount of maintenance will probably be
required to keep the mats in place. It is imperative that the mats be properly nailed/secured to the stable
natural soils to reduce the movement and increase the effectiveness of the mats. If a relatively
maintenance-free product is required, then the client should consider some other type of reinforced/armored
r [phone] • Fax [phone] • nwccl(a~mindspring.com
2580 Copper Ridge Drive • P.O. Box 775226 • Steamboat Springs, CO 80477