BOARD02056

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

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 and BLM staff,
conducted an evaluation of the stream hydrology to determine if water was physically available
for an instream flow appropriation. Although there is a substantial amount of streamflow gage
data available for the Uncompahgre Plateau and Glade Park, most of this data is severely
impacted by diversions and irrigation use. This situation makes it difficult to estimate the natural
flow regime for the watersheds on the Plateau. Without specific gage data to evaluate, the next
best approach is a regional equation that estimates annual flow characteristics. The USGS has
developed regional equations (Estimation of Natural Streamflow Characteristics in Westem
Colorado. Water Resources Investigations Report 85-4086. 1985) that apply to the Uncompahgre
Plateau and Glade Park based on basin drainage area, mean annual precipitation, mean basin
elevation and mean basin slope. The report "Uncompahgre Plateau and Glade Park Annual
Hydrograph Estimation" in Appendix C, explains staff's water availability analysis in more
detail. Table 2 below displays the estimated stream flow of Little Dolores River,

Table 2: Estimated flow Little Dolores River.
Janua Februa March A ril Ma June Jul Au ust Se tember October November December
1.4 3 4.3 65 240 110 5.5 2.1 1.8 1.7 1.6 1.5

Little Dolores River Estimated Stream Flow

10
8
6
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2
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0
JAN FEB

MAR

APR

MAY

JUN

JUL

AUG

SEP

OCT

NOV

DEe

Month

Table 2 shows that the summer flow recommendation of 2.4 cfs is only available April 1 st - July
31 st. The summer flow recommendation was further reduced to 1.6 cfs for the time period of
August 1 st through October 31 st based on limited water availability. Table 2 also shows that the
winter flow recommendation of 1.0 cfs is available from November 1 st through March 31 st.

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