ISFAPPC01711

• Case Number: 05CW0215
• Stream Name: Horsefly Creek
• Watershed: San Miguel River
• Water Division: 4
• Water District: 60
• County: Montrose
• Instream Flow App - Doc Type: Supplemental Data

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. Appendix B 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 I 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 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
Partv
BLM

BLM

Date
6/7/01
6/7/01

Q
6.36
5.98

250%-40%
15.9 - 2.5
14.9 - 2.4

Summer (3/3)
17.3(1)
13.1

Winter (213)
10.7
10.2

BLM Bureau of Land Management DOW Division ofWildJife
(1) Predicted flow outside oftbe accuracy range of Manning's Equation. ? = Criteria never met in R2CROSS Staging Table.

Biologic Flow Recommendation
The summer flow recommendation, which met 3 of 3 criteria and is within the accuracy range of the R2CROSS
model is 13.1 cfs (See Table 1). The winter flow recommendations which met 2 of 3 criteria and are within the
accuracy range of the R2CROSS model range from 10.7 cfs to 10.2 cfs (See Table 1). Averaging the two
winter flow recommendations within range results in a 10.5 cfs recommendation.

Hydrologic Data

After receiving the cooperating agency's biologic recommendation, the CWCB staff conducted an evaluation of
the stream hydrology to determine if water was physically available for an instream flow appropriation. The
hydro graph below was derived from data collected by the USGS stream gage for Horsefly Creek near Sams, CO
(ID #09173500), which has a drainage area of 28.8 square miles (See Gage Summary in Appendix C). The

dramage area of the Horsefly Creek at the confluence With the San Miguel River IS approximately 110.0 square
miles. The period ofrecord for this gage was 1942-1951, the period ofrecord used by staff in their analysis was
1942-1951, or 10 years of record. Table 2 below displays the stream flow of Horsefly Creek, in terms of a
percentage of exceedence.

Table 2: Estimated Stream Flow on Horsefly Creek
Exceedences Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dee
1% 3.8 7.6 30.6 1282.0 1661.7 354.5 9.8 35.8 18.4 13.9 14.9 2.7
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