BOARD02049

• Board Meeting Date: 1/27/2004
• Description: ISF Section - Instream Flow Appropriations - Little Cochetopa Creek
• Board Meetings - Doc Type: Memo

Biologic Flow Recommendation
The summer flow recommendations, which meet 3 of3 criteria and are within the accuracy range
of the R2CROSS model range from 2.8 cfs to 1.7 cfs (See Table 1). Averaging the two summer
recommendations within range results in a 2.25 summer recommendation. The winter flow
recommendations, which meet 2 of 3 criteria and are within the accuracy range of the R2CROSS
model range from 2.0 cfs and 0.9 cfs (See Table 1). Averaging the two winter recommendations
within range results in a 1.45 winter recommendation. 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.

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 Poncha Creek at Poncha, CO (ID #07093000), which has a drainage area
of 56 square miles (See Gage Summary in Appendix C). The total drainage area of the Little
Cochetopa Creek Drainage upstream of Spruce Creek is approximately 13.5 square miles. The
period of record for this gage was 1911-1918, the period of record used by staff in their analysis
was 1911-1918, or 7 years of record. Table 2 below displays the estimated stream flow of Little
Cochetopa Creek, in terms of a percentage of exceedence.

Table 2: Estimated flow Little Cochetopa Creek.

Estimated Lit~e Cochetopa Creek Streamflow
Exceedences January February March
1%
5%
10%
20%
50%
80%
90%
95%
99%

3.14 3.62 4.82 17.45 60.27 48.21 30.86 13.42 8.32 9.16 6.44 3.38
2.41 2.41 3.86 13.02 46.55 41.46 26.04 10.16 5.30 7.96 5.30 2.89
2.17 2.17 3.18 8.92 36.88 35.44 19.82 8.92 4.82 5.45 3.86 2.72
1.93 2.03 2.65 6.27 31.58 31.34 11.14 6.03 3.13 3.13 2.65 2.41
1.69 1.69 1.93 4.58 17.84 20.01 6.27 3.86 2.17 1.93 1.69 1.69
0.72 0.93 0.72 2.89 9.64 13.50 4.82 2.65 1.45 1.45 0.93 0.84
0.48 0.48 0.72 2.17 5.79 10.37 3.86 2.17 1.45 1.21 0.93 0.72
0.48 0.48 0.48 1.93 4.82 8.44 3.62 1.69 1.16 0.96 0.93 0.00
0.48 0.48 0.24 0.87 4.34 6.53 3.13 1.33 0.84 0.76 0.00 0.36

April

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June

July

August September October November December

Little Cochetopa Creek Estimated Stream Flow

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