Stream: Alpine Gultch Executive Summary

• Description: Stream: Alpine Gultch Executive Summary
• State: CO
• Water Division: 4
• Title: Stream: Alpine Gultch Executive Summary
• Water Supply Pro - Doc Type: Report/Study

Biological Data
Alpine Gulch is a high gradient stream with step -pool geomorphology and large substrate size.
The aquatic environment in Alpine Gulch is limited by heavy metals (aluminum) deposited into
the creek from natural sources and from historic mining activity. However, the creek is capable
of supporting brook trout and brown trout, as evidenced by BLM fishery surveys. It is unclear
whether the fish are reproducing in Alpine Gulch, or whether the fish reproduce in Henson Creek
and then utilize Alpine Gulch for cover and forage purposes. Mayfly have been consistently
observed within the creek, and this is likely the trout food source.
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 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. 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
250 % -40%
Summer 3/3
Winter 2/3
BLM
10/09/2009
2.38
6.0-1.0
4.98
1.10
BLM
10/09/2009
2.54
6.3-1.0
Out of Range
1.06
The summer flow recommendation, which meets 3 of 3 criteria and is within the accuracy range
of the R2CROSS model, is 5.0 cfs. The winter flow recommendation, which meets 2 of 3
criteria and is within the accuracy range of the R2CROSS model is 1.0 cfs.
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