6-07CW096 Supplemental Data

• Case Number: 07CW0096
• Stream Name: Willow Creek
• Watershed: Little Snake
• Water Division: 6
• Water District: 54
• County: Moffat
• Instream Flow App - Doc Type: Supplemental Data

•
Biological Data
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The BLM has conducted field surveys of the fishery resources on this stream and have found a
natural environment that can be preserved. As reported in the letter from BLM to the CWCB
"Willow Creek is a moderate gradient stream with small substrate and a stable channel. Water
quality, cover, and aquatic insects are good for supporting native fish populations." Fish surveys
indicate that the stream supports self - sustaining populations of speckled dace, mottled sculpin,
white sucker, minnow, and creek chub. This diversity of native species is unusual on streams
managed by BLM in northwest Colorado. (See BLM Fish Survey in Appendix).
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. The appendix contains copies of field
data collected for this proposed segment.
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 CDOW 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, two 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.
Table 1: Data
Party
Date
Q
250 % -40%
Summer (3/3)
Winter (2/3)
BLM
09/05/2003
1.2
3.1-0.5
2.9
2.4
BLM
09/05/2003
1.1
2.6-0.4
2.3
2.0
BLM = Bureau of Land Management DOW = Division of Wildlife
(1) Predicted flow outside of the accuracy range of Manning's Equation. ? = Criteria never met in R2CROSS Staging Table.