WSP11306

• File Number: 8027
• Description: Section D General Correspondence - Federal Agencies - BOR - Lower Missouri Region - Denver
• State: CO
• Basin: Statewide
• Date: 4/14/1978
• Author: DOI-BOR
• Title: Annual Operating Plan - Western Division - Pick-Sloan Missouri Basin Program - 1977-1978
• Water Supply Pro - Doc Type: Report/Study

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REPORT ON OPERATIONS FOR 1977

Green Mountain Reservoir

There were 125,200 acre-feet stored in the reservoir at the beginning
of the water year which was below normal. During October, releasej
for power production and downstream irrigation continued at 400 ~t /s
and 1,800 acre-feet were released to maintain a flow of 1,250 ft /s
at the3Dotsero gage through October 15. Thereafter, a release of
300 ft /s was continued through December 15 for winter ice conditons.
r,reen Mountain Reservoir's storage was below plan by the middle
of December due to below-normal winter precipit~tion and inflows.
At that time, the release was reduced to 275 ft /s and continued
until early in February. The February 1 forecast of April-July
runoff was estimated as only 56 percent of the recent 17-year average.
Although 1977 was a record-low drought year, this proved to be an
excellent early season forecast as the actual undepleted April-July
runoff into Green Mountain Reservoir was 126,000 acre-feet and
50 percent of normal. The 1977 April-July runoff of 126,000 acre-
feet was the lowest of record. Records at this station were started
in 1928. Before 1977, the record low April-July runoff was 130,000
acre-feet which occurred in 1954. Unofficial preliminary totals
of 1977 Water Year runoff for the Colorado River at the Dotsero gage
indicate a new record low since records were started in 1900. The
total runoff at the Dotsero gage in 1977 was 791,000 acre-feet.
The previous record low was 830,000 acre-feet in 1954.

After the low Feb3uary 1 forecast, the Green Mountain release was
reduced to 150 ft /s and maintained at that rate until the end of
March. During the first 2 weeks in April, snowmelt runoff devjloped
slowly, and the Green Mountain release was increased to 250 ft /s to
maintain strict replacement for senior downstream rights. From
April 15 unt~l April 28, the Green Mountain releaje varied from
98 to 350 ft /s, as required to maintain 1,250 ft /s at the Dotsero3
gage. On April 28, the Green Mountain release was reduced to 60 ft /s,
the minimum requirement for senior water rights on the B~ue River
in order to achieve the reservoir fill right. The 60 ft /s release
was continued until June 20, when hydro graph analysis indicated
that the reservoir would fill. Thereafter, with the exception of
a heavy rainfall period near the end of July, Green Mountain Reservoir
was operated for 3trict Colorado-Big Thompson replacement and to
maintain 1,250 ft /s at the Dotsero gage during the remainder of
the water year.

9

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