Stream: San Miguel River Executive Summary

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

parameters used in R2CROSS (average depth, percent wetted perimeter and average velocity)
were also used to calculate and predict the biologic instream flow recommendations.
For this segment of stream, several data sets were collected with the results shown in Table 1
below. Table 1 shows who collected the data (Party), the measured discharge at the time of the
surveys (Q), the accuracy range of the predicted flows based on Manning's Equation (240% and
40% of Q), the method used, 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
Q
Method
250 % -40%
Summer 313
Winter 2/3
BLM & CDOW
450, 325, 175, 100
PHABSIM/
RHABSIM
1125-40
500 (bluehead)
325 ( flannelmouth)*
- --
BLM & CDOW
450, 325, 175, 100
Standard R2X
1125-40
650
115
* The PHABSHWRHABSIM analysis was used to only quantify the suitable versus unsuitable
hydraulic habitat attributes of bluehead and flannel mouth sucker adults as a function of
discharge. Amounts shown reflect the discharge which produced the maximum amount of
useable habitat based on the measured mesohabitat types.
The CDOW and BLM evaluated all of the data collected to date and determined that best flow
recommendation would come from using the results from a combination of methods. PHABSIM
is a widely accepted method for quantifying the suitable versus unsuitable hydraulic habitat
attributes of selected species and life stages as a function of discharge. R2CROSS is best suited
for identifying flows with specific hydraulic criteria across riffle type habitats. The State of
Colorado has used 112CROSS extensively in the past to appropriate instream flow water rights.
CDOW and BLM were concerned that the standard R2CROSS method may not be appropriate
for this reach of the San Miguel River due to its major width (over 75' wide in most places), type
of fish species present (warm/cool water species) and its big river channel hydraulics and
characteristics.
Accordingly, BLM and CDOW staff compared results from their PHABSIM/RHABSIM data
analysis with their R2CROSS analysis. Using the results from the PHABSIM/RHABSIM data
analysis, the maximum amount of usable habitat for bluehead suckers was produced at a flow of
500 cfs, and for flannelmouth suckers at a flow of 325 cfs. The R2CROSS analysis indicated
that a spring/summer flow of approximately 650 cfs was necessary to meet all three of the
critical hydraulic criteria at this site and a fall /winter flow of 115 cfs would meet 2 of 3 of the
hydraulic criteria.
CDOW and BLM are recommending that a flow of 325 cfs, for the time period of April 15
through June 14, is the minimum amount necessary to preserve the natural environment to a
reasonable degree, for this reach of the San Miguel River. This is based on the assumption that
325 cfs would preserve 90% of the weighted useable area available to the bluehead sucker and
100% of the weighted useable area available to the flannelmouth sucker. BLM and CDOW staff
also believes a flow that maintains adequate bluehead and flannelmouth sucker habitat should
also maintain adequate roundtail chub habitat. The spring/summer flow of 325 cfs was reduced
to 170 cfs for the June 15 through July 31 time period because of water availability concerns.