7748

• UCREFRP Catalog Number: 7748
• Author: Western Water Consultants, I.
• Title: Final Report on Little Snake River Depletions by Pot Hook, Three Fork and Powder Wash Rights.
• USFW Year: 1990.
• USFW - Doc Type: Laramie, WY.
• Copyright Material: NO

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releases. If a constant demand of 800 cfs were assumed, the full demand could be met
only part of the time during the 1930-82 period. Under the Water Development Baseline,
estimated flows of the Little Snake River at the Little Snake Reservoir average only 430
cfs per month, almost half of the Powder Wash Power Plant right (800 cfs). To determine
a realistic constant power plant demand that can be met every year in the study period,
it was necessary to perform a firm yield study with WIRSOS. An initial constant demand
of 225 cfs was used in the firm yield investigation. An average monthly discharge of 225
cfs for the entire year would be sufficient to release the total active storage capacity of
1641690 AF. Additional WIRSOS runs were performed to determine the actual firm yield
discharge to be used in evaluating downstream flow impacts.
In the modeling, all demands by the Powder Wash Power Plant were met with
streamflow first and, if the water availability is insufficient, a call for storage water was
placed on Little Snake Reservoir to satisfy the remaining amount. Since the power plant
is at the dam, 100 percent of the water passed through the power plant turbines was
assumed to discharge back into the river immediately below the dam. There was no need
to include additional demands for instream flow below the dam as power releases should
satisfy instream flow requirements.
3.2.3 P&M Coal Mining Company Project
P&M owns water rights for Three Forks Reservoir and Sheep Mountain Reservoir
(See Table 1, page 6). The locations of these reservoirs are shown on Figure 2, page 7.
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