FLOOD01459

• County: Gunnison
• Community: Uncompahgre Valley
• Title: Upper Gunnison-Uncompahgre Basin Phase 1 Feasibility Study Summary Report
• Date: 5/1/1989
• Prepared For: Colorado Water Resources and Power Development Authority
• Prepared By: HDR Engineering, Inc.
• Floodplain - Doc Type: Project

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agricultural shortages and instream flow deficiencies still remained with the
reservoi rs assumed to be in pl ace. The results al so suggested that the
shortages could be el iminated or reduced by moving to storage sites further
upstream on Tomichi and Cochetopa Creeks. Therefore, Scenario 2B evaluated a
combination of Castleton, Sargents No.3, and Pauline reservoirs.

The storage of water in these reservoi rs was assumed to occur under
conditional decrees held by the Upper Gunnison River Water Conservancy
District, assuming they could be transferred to the proposed reservoir site if
required. The reservoirs were operated to alleviate agricultural supply
shortages and to meet enhanced instream flow targets. Releases were made on
demand to satisfy both water uses. Otherwise the reservoirs were allowed to
store water in priority and to spill when full.

The enhanced i nstream flow targets were developed from stat i st ics of
natural flow on Ohio, Tomichi, and Cochetopa Creeks and are based on fishery
and recreational considerations. On all streams the enhanced instream flow
targets are equal to or higher than the CWCB decreed val ues. Enhanced
instream flow targets were developed for each modeled reach on each of the
three tributaries. However, usually only one reach on each tributary acted as
the controlling reach, calling instream flow water through the other reaches
and satisfying them in the process. The controlling reaches and their
associated flow targets are:

Ohio Ck. at Mouth
Tomichi Ck. Above Razor Ck.
Cochetopa Ck. Above Los Pinos Ck.

29 cfs year-round
18 cfs Oct-Mar, 31 cfs Apr-Sep
9 cfs Oct-Mar, 15 cfs Apr-Sep

The hydrologic performance of each in-basin reservoir was evaluated
mainly by assessing agricultural shortages and instream flow conditions on the
respective streams. Recreation potential of the reservoirs was evaluated by
examining reservoir level fluctuations. Basin-wide effects were identified by
evaluating conditions at several other key stream reaches, storage reservoirs,
and points of diversion in the basin.

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