PROJ00533

• Contract/PO #: C153367
• Contractor Name: International Engineering Company
• Water District: 0
• County: Rio Blanco
• Bill Number: XB 99-999
• Loan Projects - Doc Type: Feasibility Study

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Minimum streamflows of 120 cfs on the North Fork and 200 cfs on the mainstem
to the confluence with Piceance Creek were provided, if possible. Meeting
120 cfs or the historic minimum flow in the North Fork presented no
operational difficulty except in the extremely dry winter months of 1977-78,
during which nine months of historic flow were below 120 cfs. During that
period of the study, six months of 90 cfs instream flows were imposed some
10 to 20 cfs below historic flows. Inspection o~ the full study period
showed that only in years in which the June reservoir level was less than
40,000 acre-feet would such a reduction below the historic flows be
necessary in the following winter months. In all other cases, carryover
storage was sufficient to maintain the minimum flows.

Minimum streamflows of 200 cfs were provided below the junction of the North
and South Forks. This flow was present in the stream down to the confluence
with Sheep Creek during all summer months. At Sheep Creek, water was
diverted to Piceance Creek for use in the oil shale industry. Below that
diversion, the flows fell below 200 cfs a number of times, but were reduced
below 150 cfs in only six months. Four of those months were in the extrem~
dry year of 1977.

The operation of Avery and Sawmill Mountain Reservoirs is also affected by
the size of the diversion works and intake pipeline. For economic reasons,
it is desirable to use the smallest intake which will satisfy the storage
requirements. An analysis was made of the relationships of monthly capacity
for storage to the divertible flow in the North Fork at the decreed
diversion points. It was found that the streamflows on the North ForI<
exceeded a divertible flow of 250 cfs in only eight out of the 324 months in
the study period. Since the monthly flows do not reflect daily peaks, it
was decided to use this flow rate for intake design. Future analysis of
daily flows, which was beyond the scope of this study, may result in some
reduction of intake capacity with a corresponding decrease in costs.

The results of the operation studies for lIvery and Sawmi 11 Mountain sites
are almost identical because of the proximity of the reservoir sites and
corresponding diversion points. Figure V-3 illustrates the fluctuations of