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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93 percent of average, and the April-July runoff forecast volume increased
to 180,000 acre-feet.

Adams Tunnel diversions to the east slope continued near capacity through
March 16 ~nd were 132 percent of average. The diversions were shutdown
for 38 days on March 17 due to scheduled maintenance on Olympus Tunnel and
Pole Hill Powerplant, Afterbay, and Power Canal. Marys Lake Powerplant
annual maintenance, Lake Estes silt removal, and Olympus Dam radial gate
maintenance were also conducted during this time.

Lake GranbY storage continued to decl ine until March 16 when minimum
storage for the year was reached at 136,680 acre-feet (water surface
elevation '8206.36 feet). Granby storage continued to be below normal as
the March 31 storage level was 167,839 acre-feet below the 1960-1989
average.

April was a wet month as precipitation was 126 percent of average. The
May 1 snbwpack was 90 percent of average and with the increased
precipitat~on, this further increased the April-July runoff forecast
volumne t9 195,000 acre-feet.. Due to much above normal precipitation,
April inflpw was high at 129 percent of average. Inflows rose sharply by
the end of'May and were at 1,303 ft3js on May 31:

With waterfpumped from Willow Creek and natural inflow on the rise, storage
began a gr~dual climb reaching 185,414 acre-feet by May '31. May continued
to be wet as precipitation was 124 percent of average.

Natural inflow increased rapidly in early June and peaked at 2,694 ft3/s
on June 12.' Precipitation was much below normal for June at 26 percent of
average, bpt inflow was 105 percent of average. Lake Granby storage
continued to rise reaching 291,042 acre-feet by June 30. However, this
was 138,158 acre-feet below the 3D-year average.

Adams TunnEll diversions were only 36 percent of average in June to take
full advantage of "skim" water on the Big Thompson River and project
deliveries were below normal.

Natural inflows were low in July at only 69 percent of average. By the
end of thei month, natural inflow averaged only 220 ft3jS. However,'
precipitati!>n was above average at 128 percent of average. Total release
to the Colorado River was equal to the bypass release for minimum required
fish habit~t release. Lake Granby storage reached the peak . of
301,346 acr~-feet (elevation 8242.61 feet) on July 13 and this was
238,454 acre-feet below maximum storage.

During July, Adams Tunnel diversions were 50 percent of average at
10,000 acre1feet to meet project water deliveries which were much below
average, to !Daintain desirable storage level s in Carter Lake and Horsetooth
Reservoi rs, \ and to take full advantage of "skim" water. For August,
diversions ~hrough Adams Tunnel continued low at 6,900 acre-feet for the
month to maiptain terminal reservoir storage, to continue diverting "skim"
water, and to meet below normal irrigation deliveries. August inflows were
84 percent of average and precipitation was 86 percent of average;

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