WSP00432

• File Number: 8441.700
• Description: Colorado Big Thompson Project - Annual Operating Plans
• Basin: South Platte
• Water Division: 1
• Date: 1/1/1990
• Title: Annual Operating Plans - Colorado Big Thompson Project - Water Year 1990-1991
• Water Supply Pro - Doc Type: Report/Study

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SUMMARY OF 1990 OPERATIONS

Water year 1990 runoff was below average throughout the Colorado-Big
Thompson ~roject (Project) varying from 64 percent of average for the inflow
into Willow Creek Reservoir to 93 percent of average into lake Estes.

Peak i nfl ows to reservoi rs wi thi n the Project occurred in 1 ate May and
mid-June and were near normal except for Willow Creek Reservoir. On May 24,
inflow to'Willow Creek Reservoir peaked at 373 ft3/s. The inflow to Green
Mountain peaked on June 12 at 2,051 ft3/s. Inflow to lake Granby peaked at
2,694 ft3/s and the lake Estes inflow peaked at 968 ft3/s, both occurring on
June 12.

River rel~ases from Willow Creek Reservoir and lake Granby were made to
meet only ,minimum required releases for fish habitat. The maximum release
at lake Estes for the water year was 370 ft3/s on June 13 to bypass inflow.
Project ~eliveries p'eaked on October 29 at 442 ft3/s at Horsetooth
Reservoir; and 380 ft3/s at Carter lake on August 12 and 13. The maximum
release at Green Mountain Reservoir was 1,317 ft3/s on September 1 and the
maximum project delivery of 455 ft3/s to the Big Thompson River occurred
on October 21.

Water year preci pi tat i on total s for October-September vari ed from 85 percent
of averag~ on the Green Mountain watershed to 119 percent of average on the
Poudre watershed.

Winter pr$cipitation (October-January) on the Project was below average
at 71 per4ent of average. On October 15, the Green Mountain Dam station
recorded Q.96 inches of precipitation due to rain mixed with snowfall.
Snow and rain occurred at Estes Park on October 15 and 0.60 inches of
preci pi tat!i on was recorded. The lake Granby and Wi 11 ow Creek watersheds
received the first significant rain mixed with snowfall of the water year
on October 16 with 0.60 inches of precipitation being recorded. Only one
significa~t daily snowfall above 0.50 inches was recorded on the Project
in Decemb~r, January, and February, and this was 0.68 inches at Flatiron
on Decemb~r 10. Project watersheds averaged only 42 percent of average
preci pi tatii on for January. The lake Estes and St. Vra in watersheds
recorded b~low normal precipitation for January at 28 percent of average.
February continued to be dryas the Green Mountain watershed was below
normal at only 51 percent of average precipitation.

A major snpwstorm hit the Project area from March 5 through March 7, with
0.61 inches of precipitation recorded at Green Mountain, 1.00 inches of
precipitat~on recorded at lake Granby, 2.10 inches of precipitation
recorded at lake Estes, 2.53 inches of precipitation recorded at Flatiron,

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