ISFAPPC01452 ‎(2)‎

• Case Number: 04CW0082
• Stream Name: East Branch Sayres Gulch
• Water Division: 2
• Water District: 11
• County: Chaffee
• Instream Flow App - Doc Type: Supplemental Data

Biologic Flow Recommendation
The flow recommendation, which meets 2 of 3 criteria and is the only flow within the accuracy
range of the R2CROSS model since the 1.00 ft/sec average velocity criterion is never met in the
R2CROSS staging table. That flow recommendation is 1.0 cfs (See Table 1). CDOW therefore
has recommended a year-round instream flow of 1.0 cfs. 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 Halfmoon Creek near Malta, CO (ill #07083000), which has a drainage
area of 23.6 square miles (See Gage Summary in Appendix C). The total drainage area of the
East Branch Sayres Gulch Drainage is approximately 2.75 square miles. The period of record
for this gage was 1946-1998, the period of record used by staff in their analysis was 1946-1998,
or 52 years of record. Table 2 below displays the estimated stream flow of East Branch Sayres
Gulch, in terms of a percentage of exceedence.

Table 2: Estimated flow East Branch Sayres Gulch.

Exceedences J
1%
5%
10%
20%
50%
80%
90%
95%
99%

anuary February are ~pril av une U1V uaust eDtem er eto er ovem er eeem er
1,05 0.93 1.28 3.03 18.63 34.14 34.49 15.61 5.84 3.03 2.21 1.17
0,80 0.72 0.82 1.86 13,75 27.97 23.12 9,56 3.96 2.33 1.51 1.03
0.65 0.61 0.70 1.51 10,60 24.47 18.88 7.19 3.38 2.10 1.28 0.88
0.58 0.52 0.52 1.00 8.16 20,86 13.75 5.36 2,80 1.63 1.07 0.75
0.44 0.41 0.41 0.65 4.31 13.75 8,16 3.50 1,86 1.17 0.80 0,56
0.35 0.31 0.30 0.41 1.63 9.21 4.89 2.33 1.40 0,87 0.63 0.45
0.29 0.28 0.27 0.31 1.07 7.46 3,73 1.98 1.17 0.78 0.57 0.41
0.24 0.23 0.17 0,28 0.80 6.29 3.03 1.75 1.03 0,71 0.51 0.37
0.17 0.20 0.14 0.20 0.57 4.03 2.23 1.40 0.81 0.60 0.40 0.31

M h A

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bOb N

b D

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East Branch of Sayres Gulch Estimated Stream Flow

2

1.5

~ 1
o

0.5

o

JAN

FEB

MAR

AA'l

MAY

JUN

JlA.

AUG

SEP

OCT

~

DEe

Month

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