WSP03460

• File Number: 8441.700
• Description: Colorado Big Thompson Project - Annual Operating Plans
• Basin: South Platte
• Water Division: 1
• Date: 1/1/1989
• Title: Annual Operating Plans - Colorado Big Thompson Project - Water Year 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 ar-e located on the Blue River- on
Colorado's western slope. The r-eservoir provides replacement storage
for- out-of-pr-iority depletion by the Pr-oject.

Construction was completed in 1943. The reservoir has a total capacity
of 154,645 acre-feet, wi th 52,000 acr-e-feet allocated to r-eplacement
storage. The balance of about 100,000 acre-feet (inc 1 ud i ng 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 reser-voir elevations. The spillway on the left
abutment is gated with three r-ad i a 1 gates and has a total r-e 1 ease
capability of 25,UOO ft3/s.

Reservoir- storage coming
95,542 acre-feet compar-ed
128,400 acr-e-feet.

Colorado River flows wer-e below nor-mal dur-ing October- averaging 977 ft3/s
at the Dotsero gauge and 1,770 ft3/s at the Cameo gauge. This flow
was not adequate to meet downstream water user demands and r-esulted in
the need for a call on Gr-een Mountain Reservoir to maintain the required
flow of 1,850 ft3/s at the Cameo gauge through the October- 20 irr-igation
season. Tur-bine 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 water year- 1989
to an average September

was equal to
30 stor-age of

Winter turbine releases (November- through Januar-y) averaged near-
191 ft3/s to meet replacement requirements, power- pr-oduction, and the
desir-ed end-of-Januar-y stor-age position. Gr-een Mountain Reser-voir-
dr-awdown was scheduled to meet normal target stor-age levels. The
end of Januar-y stor-age for- Dillon Reser-voir was equal to
233,292 acre-feet.

Winter pr-ecipitation was below nor-mal, and the Febr-uar-y 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 per-cent of the r-ecent 30-year- (1959-1988)
average. Reservoir- storage continued close to plan dur-ing February, and
releases were decreased to about 150 ft3/s. Precipitation for February
was much above normal at 160 per-cent of average.

Conditions turned drier in Mar-ch with 87 percent of average precipitation
recor-ded. This reduced the Apr-il 1 forecast of the April-July
runoff vo 1 ume to 225,000 acre-feet. A lthough it was dr-y, reservoi r
inflow was above normal at 121 per-cent of aver-age for- Mar-ch.

Dur-ing April, the snowpack r-educed to 71 percent of average and the
April-July for-ecast was subsequently r-educed to 205,000 acre-feet.
April precipitation was above nor-mal at 123 per-cent of aver-age as were

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