BOARD02438

• Board Meeting Date: 1/25/2005
• Description: ISF Section - Instream Flow Appropriations - Maggie Gulch
• Board Meetings - Doc Type: Memo

Biologic Flow Recommendation

The summer flow recommendation, which meets 3 of 3 criteria and is within the accuracy range
of the R2CROSS model is 2.5 cfs (See Table 1). The winter flow recommendation, which meets
2 of 3 criteria and is within the accuracy range of the R2CROSS model is 1.5 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 in stream 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 hydrograph below was derived from data collected by the
USGS stream gage for Animas River at Howardsville, Colorado (ID #09357500), which has a
drainage area of 55.90 square miles (See Gage Summary in Appendix C). The total drainage
area of Maggie Gulch is approximately 5.5 square miles. The period of record for this gage was
1935 to 1982, the period of record used by staff in their analysis was 1935 - 1982, or 47 years of
record. Table 2 below displays the estimated flow of Maggie Gulch at the gage, in terms of a
percentage of exceedence.

Table 2: Estimated Stream Flow in Maggie Gulch
Exeeedenees Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nav Dee
10/0 2,5 2,2 3,2 21,9 69,9 103,9 74,3 26,9 21,5 14,9 6,2 3,1
50/0 2,2 2,0 2,2 14,3 55,2 80,3 55,9 15,6 13,1 8,2 4,3 2,7
10% 2,0 2,0 2,0 10,1 48,7 72,9 45,1 13,1 9,7 6,5 3,9 2.4
20% 1,9 1,8 1,8 7,2 38,8 62,1 32,2 10,7 6.4 4,9 3,3 2,2
80% 1.4 1,3 1,3 1,8 10,2 25.4 8,5 4,1 2,9 2,2 1,7 1,5
90% 1,3 1,2 1,1 1,5 7,1 20,6 6,2 3.4 2,6 1,9 1,6 1.4
95% 1,2 1,1 1,1 1,3 5,2 18,0 4,9 3,1 2,3 1,8 1,5 1,3
99% 1,0 1,0 1,0 1,1 2.4 11,3 3,7 2,5 1,9 1,5 1,2 1,1

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