ISFAPPC01496

• Case Number: 02CW0276
• Stream Name: Royer Gulch
• Watershed: San Miguel River
• Water Division: 4
• Water District: 60
• County: San Miguel
• Instream Flow App - Doc Type: Supplemental Data

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Biologic Flow Recommendations
The CD OW recommended a 1.3 cfs summer and winter flow for the segment based on the
October st\ 1996, data collection efforts.

Staff reviewed the data collected by the CDOW. The summer flow recommendation for the
proposed reach, which meets 3 of 3 criteria but is outsid(: the accuracy range of the R2CROSS
model is 2.7 cfs. The winter flow recommendation for the proposed reach, which meets 2 of 3
criteria and is within the accuracy range of the R2CROSS model is 1.3 cfs (See Table 1). It is our
belief 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. In these cases, CWCB staff relies upon the
biological expertise of the cooperating agencies to develop a biologic instream flow
recommendation.

The CD OW has indicated that this is a high priority stream segment to them. However, because
the summer recommendation falls outside the accuracy range of the R2CROSS model, staff
believes that more data needs to be collected to accurately predict the summer flow
recommendation. Staff has consulted with the recommending agency and believes that it would
be appropriate for the Board to file on a year-round flow of 1.3 cfs, if water was available (See
Table 1).

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. There are no currently operated or historically operated
streamflow gages for this reach. The closest gage CWCB staff found was the gage located on the
San Miguel River 5.0 miles west of Royer Gulch drainage. The hydro graph below was derived
from data collected by the USGS stream gage for the San Miguel River near Telluride, CO (ill
#09171200), which has a drainage area of 42.S square miles. The drainage area of Royer Gulch
is approximately 1.0 square miles. Staff used a basin apportionment method to estimate stream
flows for Royer Gulch (See Gage Summary in Appendix C). The period of record for this gage
was 1959 to 1965, the period of record used by staff in their analysis was 1959 - 1965, or six
years of record. Table 2 below displays the estimated flow of Royer Gulch above the San
Miguel River, in terms of a percentage of exceedence.

Table 2:

Estimated Royer Gulch Stream Flow
Exceedences
1%
5%
10%
20%
50%
80%
90%
95%
99%

Januarv Februarv March ADril Mav June Julv AU<lust Seotember October November December
0.43 0.48 1.20 2.48 9.61 11.13 9.90 4.88 2.20 1.15 0.79 0.55
0.40 0.45 0.73 2.14 8.29 9.86 8.51 2.87 1.73 0.94 0.69 0.48
0.38 0.45 0.56 1.85 5.67 8.55 6.38 2.24 1.54 0.90 0.67 0.45
0.38 0.43 0.48 1.45 4.39 7.36 4.78 1.81 1.33 0.78 0.62 0.43
0.36 0.36 0.38 0.83 2.83 5.51 2.30 1.21 0.88 0.64 0.52 0.40
0.33 0.33 0.33 0.52 1.66 3.14 1.31 0.93 0.64 0.55 0.48 0.38
0.31 0.33 0.33 0.38 1.04 2.76 1.06 0.78 0.62 0.52 0.45 0.38
0.31 0.33 0.33 0.38 0.86 2.38 0.96 0.69 0.59 0.52 0.45 0.31
0.31 0.33 0.29 0.38 0.69 1.91 0.78 0.64 0.57 0.50 0.43 0.31