Stream: South Fork Slater Creek ‎(Lower Segement)‎ Executive Summary

• Description: Stream: South Fork Slater Creek ‎(Lower Segement)‎ Executive Summary
• State: CO
• Water Division: 6
• Title: Stream: South Fork Slater Creek ‎(Lower Segement)‎ Executive Summary
• Water Supply Pro - Doc Type: Report/Study

Biological Data
In July and September of 2009 TU and CDOW collected stream cross sectional data, natural
environment data, and other data needed to quantify instream flow needs. Previous survey data
collected by CDOW indicated the stream supports healthy populations of Colorado River
cutthroat trout, brook trout and molted sculpin.
Field Survey Data
TU and CDOW 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 now 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)
CDOW /TU
7/8/2009
9.59
24.0-3.8
38.8*
6.5
CDOW/TU
9/17/2009
1.71
4.3-0.7
14.2*
4.0
* Values are outside of the range of the R2Cross model.
The R2Cross data from the two cross sections indicate that the fishery of this segment of SF
Slater Creek can be protected with summer flows between 14.2 and 38.8 cfs and winter flow of
5.25 cfs. However, the summer flow recommendations were greater than 2.5 times the field
measured discharge and therefore, were considered outside of the modeling accuracy of
R2Cross. The recommenders used the sum of the summertime instream flow recommendation
from West Prong Slater Creek above Decker Ditch (4.9 cfs) together with the summertime
-3-