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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the report are designed for the highest velocities modeled and as such can be implemented at any
point along the study reach,
7. A toe protection detail and typical riprap specification is provided in the report, A potential
source of the riprap is identified, Material and placement costs are estimated for different
scenarios that offer varying levels of protection,

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Limited Watershed Studv:

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I. A flood frequency analysis was performed by CWCB using 20 years of streamflow data at the
Milner gage on the Elk River. Resulting flows at this location indicate that the 100-year flow is
6.190 cfs and the 5~year flow is 4,770 cfs, The peak flow from the 1997 flood event at the Milner
gage was estimated to be 5,370 cfs. or between a 10- to 50-year event.
2, It is estimated that approximately 41 % of the average basin runoff originates from the Park Range,
3, Steamboat Lake controls about 8% of the Elk River drainage basin and is not currently operated as
a flood control reservoir. In order to provide flood control, the operation of the reservoir would
need to be changed, and it is likely that structural changes to the service spillway andlor
emergency spillway would be required, This would negatively impact the recreational and
fisheries mission of the reservoir, Resulting flood protection at the lower extremes of Elk River
would only be marginally improved,
4, Gage information along the Elk River and Willow Creek was used to perform a travel time
analysis for determining a relationship between Steamboat Lake releases during the June 1997
flood event and the Elk River discharge at the Milner gage, Our results indicate that the
approximate travel time between Steamboat Lake and the Milner gage is around 7 hours. Daily
reservoir peak release rate information for Steamboat Lake indicates that between 250 cfs and 280
cfs were released during June I" and June 2", Therefore. it appears that discharge from
Steamboat Lake contributed to about 5% of the total peak flow (5370-cfs) at the Milner gage
during the 1997 flood event. This flow amount is less than the 400 cfs that the USGS determined
had overflowed County Road 42 just upstream of the Milner gage,

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ICON Engineering Inc. wishes to acknowledge the assistance of the project sponsors and the many
interested parties that have provided data and analysis contributing to this report,

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Submitted by:

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ICON Engineering, Inc.

By:

By:

Terri Fead, PE
Project Manger

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Penn Gildersleeve. PE
Principal ]n Charge

By:

Craig Jacobson, EIT
Project Engineer

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