WSP09032

• File Number: 8407
• Description: Platte River Basin - River Basin General Publications
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 2/27/1991
• Author: BOR
• Title: Annual Operating Plans - North Platte Project Water Years 1990-1991
• Water Supply Pro - Doc Type: Report/Study

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WATER YEAR 1990 OPERATIONS

Green Mountain Reservoir

Green Mountain Reservoir and Powerplant are located on the Blue River on
Colorado's western slope. The reservoir provides replacement 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 25,000 ft3/s.

,Reservoir storage coming into water year 1990 was equal to 97,985 acre-feet
compared to an average September 30 storage of 128,400 acre-feet.

Colorado River native flows were below normal during October averaging
825 ft3/s at the Dotsero gauge and 1,571 ft3/s at the Cameo gauge. This
flow 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 through the October 28 irrigation
season. Turbine releases averaged 616 ft3/s for October 1-28 when the call
was on, and 211 ft3/s for October 29-31 when the call was off.

Winter turbine releases (November through January) averaged near 160 ft3/s
to meet replacement requirements, bypass of inflow, power production, and
the desired end-of-January storage position. Green Mountain Reservoir
drawdown was scheduled to meet the normal target storage level of near
65,000 acre-feet for April 30,

The end of January storage for Di 11 on Reservoi r was equa 1 to
225,830 acre-feet.

The October-January precipitation was much below normal at 54 percent of
average, and the February 1 snowpack data was recorded at 88 percent of
average.

The February 1 forecast of the April-July runoff volume totaled
240,000 acre-feet which was 89 percent of the recent 30-year (1960-1989)
average. Reservoir storage continued close to plan during February, and
releases continued at about 160 ft3/s. Precipitation for February continued
to be much below normal at 51 percent of average. This reduced the March 1
forecast of the April-July runoff volume to 210,000 acre-feet.

Snowfall greatly increased in March with 110 percent of average
precipitation recorded. Although it was a wet month, reservoir inflow was
below normal at 59 percent of average for March.

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