WSP00886

• File Number: 8407
• Description: Platte River Basin - River Basin General Publications
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 4/16/1990
• Author: BOR
• Title: Annual Operating Plans - North Platte Project Water Years 1989-1990
• Water Supply Pro - Doc Type: Report/Study

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WATER YEAR 1989 OPERATIONS

Green Mountain Reservoir

Green Mountain Reservoir and Powerplant are located on the Blue River on
Co lorado I s western slope. The reservoi r provides rep 1 acement storage
for out-of-priority depletion by the Project. .

Construction was completed in 1943. The reservoir has a total capacity
of 154,645 acre-feet, with 52,000 acre-feet allocated to replacement
storage. The balance of about 100,000 acre-feet (including dead and
inactive storage) is allocated to power, natural flow shortage makeup,
and other water uses. The powerplant has two units with a total
installed capacity of 25.8 megawatts and a release capability of about
1,725 ft3/s, at low reservoir elevations. The spillway on the left
abutment is gated with three radial gates and has a total release
capability of 25,UOO ft3/s.

Reservoi r storage comi ng
95,542 acre-feet compared
128,400 acre-feet.

Colorado River flows were below normal during October averaging 977 ft3/s
at the Dotsero gauge and 1,770 ft3/s at the Cameo gauge. Thi s fl ow
was not adequate to meet downstream water user demands and resulted in
the need for a call on Green Mountain Reservoir to maintain the required
flow of 1,850 ft3/s at the Cameo gauge throu9h the October 20 irrigation
season. Turbine releases averaged 341 ft3/s for October 1-20 when the
call was on, and 226 ft3/s for October 21-31 when the call was off.

into
to an

water year 1989 was
average September 30

equa 1 to
storage of

Winter turbine releases (November through January) averaged near
191 ft3/s to meet replacement requirements, power production, and the
desired end-of-January storage position. Green Mountain Reservoir
drawdown was schedu led to meet normal target storage levels. The
end of January storage for Dillon Reservoir was equal to
233,292 acre-feet.

Winter precipitation was below normal, and the February 1 snowpack data
was recorded at 84 percent of average.

The February 1 forecast of the April-July runoff volume totaled 240,000
acre-feet which was 90 percent of the recent 30-year (1959-1988)
average. Reservoir storage continued close to plan during February, and
releases were decreased to about 150 ft3/s. Precipitation for February
was much above normal at 160 percent of average.

Conditions turned drier in March with 87 percent of average precipitation
recorded. This reduced the April 1 forecast of the April-July
runoff volume to 225,000 acre-feet. Although it was dry, reservoir
inflow was above normal at 121 percent of average for March.

During April, the snowpack reduced to 71 percent of average and the
April-July forecast was subsequently reduced to 205,000 acre-feet.
April precipitation was above normal at 123 percent of average as were

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