Stream: Cochetopa Creek ‎(Upper Segement)‎ Executive Summary

• Description: Stream: Cochetopa Creek ‎(Upper Segement)‎ Executive Summary
• State: CO
• Water Division: 4
• Title: Stream: Cochetopa Creek ‎(Upper Segement)‎ Executive Summary
• Water Supply Pro - Doc Type: Report/Study

Biological Data
This segment of Cochetopa Creek is a moderate to high gradient stream, with moderate substrate
size, punctuated by occasional boulders. The lower portion of the proposed reach is confined by
a narrow canyon, but the upper portion of the reach meanders through a broader valley,
supporting extensive wetland communities on the valley floor. The riparian community is in
good condition and is composed primarily of willow communities in the upper part of the reach
and spruce- willow communities in the lower part of the reach. The upper part of the reach
provides good pools and overhanging banks for overwintering, while the lower part of the reach
confined to a canyon is comprised mainly of riffle and run habitat. Fishery surveys indicate that
the creek supports a self - sustaining population of brown, brook, and rainbow trout. The survey
revealed a variety of age classes and individual specimens up to 12 inches in length.
Field Survey Data
BLM staff used the R2Cross methodology to quantify the amount of water required to preserve
the natural environment to a reasonable degree. The R2Cross method requires that stream
discharge and channel profile data be collected in a riffle stream habitat type. Riffles are most
easily visualized, as the stream habitat types that would dry up first should streamflow cease.
This type of hydraulic data collection consists of setting up a transect, surveying the stream
channel geometry, and measuring the stream discharge.
Biological Flow Recommendation
The CWCB staff relied upon the biological expertise of the cooperating agencies to interpret
output from the R2Cross data collected to develop the initial, biologic instream flow
recommendation. This initial recommendation is designed to address the unique biologic
requirements of each stream without regard to water availability. Three instream flow hydraulic
parameters, average depth, percent wetted perimeter, and average velocity are used to develop
biologic instream flow recommendations. The CROW has determined that maintaining these
three hydraulic parameters at adequate levels across riffle habitat types, aquatic habitat in pools
and runs will also be maintained for most life stages of fish and aquatic invertebrates (Nehring
1979; Espegren 1996).
For this segment of stream, four data sets were collected with the results shown in Table 1
below. Table 1 shows who collected the data (Party), the date the data was collected (Date), the
measured discharge at the time of the survey (Q), the accuracy range of the predicted flows
based on Manning's Equation (240% and 40% of Q), the summer flow recommendation based
on meeting 3 of 3 hydraulic criteria and the winter flow recommendation based upon 2 of 3
hydraulic criteria. It is believed that recommendations that fall outside of the accuracy range of
the model, over 250% of the measured discharge or under 40% of the measured discharge may
not give an accurate estimate of the necessary instream flow required.
Table 1: Data
Party
Date
Q
2501%► -40%
Summer 3/3
Winter 2/3
BLM
10/07/2005
19.14
47.9-7.7
9.66
Out of Range
BLM
9/26/2006
15.81
39.5-6.3
11.27
Out of Range
BLM
10/07/2008
11.48
28.7-4.6
10.11
6.36
-3-