BOARD00154 ‎(2)‎

• Board Meeting Date: 3/13/2007
• Description: ISF Section - Notice of 2008 Instream Flow Recommendations and Summary of ISF Workshop
• Board Meetings - Doc Type: Memo

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DOW & TU 6/7/06 9.80 24.5 - 3.9 4.1 2.0lUK)
TU 7/5/06 1.35 3.4 - 0.5 1.7 0.6
TU 7/5/06 1.35 3.4 - 0.5 3.0 2.0

DOW = Division of Wildlife TU = Trout Unlimited

OR = Outside ofR2X Confidence Range

Biologic Flow Recommendation
The summer flow recommendations, which met 3 of 3 criteria and were within the accuracy
range of the R2CROSS model, ranged from 4.1 cfs to 1.7 cfs. Averaging the summer values
within range, results in a 2.9 cfs summer recommendation (See Table I). The winter flow
recommendations, which met 2 of 3 criteria and were within the accuracy range of the
R2CROSS model, range, ranged from 2.0 cfs to 0.2 cfs. Averaging the winter values within
range, results in a 0.8 cfs winter recommendation (See Table I).

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Hydrologic Data

The CDOW statT conducted a preliminary 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 South S1. Vrain Creek near Ward, CO
(#06722500), which has a drainage area of 14 square miles (See Gage Summary in Appendix C)
and the Streamflow Statistics Report for the drainage basin of Como Creek, which has a drainage
area of 4.1 square miles (See Streamflow Statistics Report in Appendix C). The total drainage
area upstream of this ISF segment of Como Creek is 4.1 square miles. The period of record for
the South S1. Vrain Creek gage was 1925 to 1973, the period of record used by statT in their
analysis was 1925 to 1973, or 24 years of record. 1 Table 2 below displays the estimated flow of
Como Creek at the lower terminus of the instream flow reach in terms of a percentage of
exceedence.

Table 2: Estimated Stream Flow for Como Creek

Exceedences
0.01
0.05
0.10
0.20
0.50
0.80
0.90
0.95
0.99

Jan....ry February March April May June July AUllUSl Seotember Octctler November December
1.71 1.42 1.71 5.98 60.48 79.38 61.70 34.65 12.39 7.12 3.42 2.26
1.47 1.42 1.71 5.69 31.15 61.22 50.11 22.78 1025 5.41 2.95 2.26
1.42 1.14 1.42 4.27 22.76 53.53 41.57 17.37 6.54 4.56 2.85 1.71
1.14 1.03 1.05 2.85 17.08 48.41 31.32 14.24 7.12 3.99 1.94 1.28
0.71 0.63 o.n 1.28 8.54 34.17 20.22 9.88 4.84 2.79 1.42 0.88
0.57 0.51 0.57 0.85 3.42 21.92 12.61 6.63 3.13 1.75 0.94 0.85
0.48 0.43 0.48 0.71 2.22 17.08 10.25 5.41 2.79 1.31 0.80 0.57
0.43 0.39 0.43 0.85 1.85 14.52 9.17 4.56 2.35 1.03 0.68 0.51
0.37 0.31 0.37 0.57 1.22 11.39 7.81 3.42 1.74 0.85 0.57 0.50

USGS
Streamfl()N Janua FebnJa
Stallstlcs 0.47 0.45

March
0.57

June
20.6

October November December
1.1 0.76 0.56

Average

0.59

0.54

0.67

1.44

9.42

27.38

13.20

5.63

3.05

1.95

1.09

0.72

Table 2 shows that the summer flow recommendation of 2.9 cfs is available at least 50% of the
time for the months of May through July. The winter flow recommendation of 0.8 cfs is not
available at least 50%. Based on this water availability analysis, the summer recommendation
was further reduced to 1.1 cfs August I through October 15 and April I through April 30 and the
winter recommendation was further reduced to 0.45 cfs for the time period of October 16

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I Only data for the following years was available 1925-27, 1928-31, 1954-73.

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