FLOOD02750

• Document ID: 125
• County: Routt
• Stream Name: Elk River
• Basin: Yampa/White
• Water Division: 6
• Title: Streambank Stabilization Limited Watershed
• Date: 11/1/1999
• Prepared For: CWCB
• Prepared By: ICON Engineering, Inc.
• Watershed Pro - Doc Type: Educational/Technical/Reference Information

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5.1

5.2

SECTION 5
ALTERNATIVE ANALYSIS

GENERAL

This section describes alternative measures considered for stabilization efforts along the lower
0.9 miles of the Elk River. The alternatives considered were based on results of both the
geomorphic and hydraulic analyses. While many other measures are available for both bed and
bank stabilization, the measures described in this section were chosen to meet the goals of
providing a more stable channel that has some potential of enhancing habitat diversity along the
corridor.

In general, the stream is characterized as a sinuous point bar channel along this reach. It is
recommended that no major plan form modifications take place. Minor adjustments to the
existing channel features may take place in an effort to modify sinuosity along the channel for
enhancement of relative morphologic stability.

CONCEPTUAL AL TERNA TIVE ANALYSIS

Alternative analysis for this study concentrated on the areas where stability of the channel
appears to be threatening both public and private structures. This limited improvements to
Reaches 2 and 3, upstream of U.S. 40.

5.2.1 Constraints

Several existing constraints affected the selection of the protection measures considered. These
included the proximity of existing lateral and vertical controls, the hydraulic parameters within
the reach, the existing channel geometry, the local site conditions, and the severitY of the
stability problems with respect to existing structures.

The 100-year discharge was used for design purposes, since it resulted in one of the highest
channel velocities through the reaches where protection was being considered. The 500-year
discharge resulted in slightly higher velocities, but the 100-year frequency was considered a
more reasonable level of protection. Velocities were a major consideration in selection of
appropriate stabilization measures. At Section 5, a velocity distribution across the channel
section indicated that velocities would exceed 12 fps (see Appendix G and refer to Table 3.3).
This range of velocities appears to be excessive for the performance of many bioengineering
applications (Biedenharn, et.al., 1997). Therefore, alternatives focused on more structural
measures with the potential for vegetative enhancement.

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