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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The Big T;hompson River inflow, that was in excess of the minimum required
outflow ~elow Lake Estes, was diverted as skim water through Olympus Tunnel
on April :25 and continued as available through September.

Snowpack ;in the Big Thompson River Basin was measured at 9.9 inches or
93 percernt of average on May 1. Most probable forecasted natural inflow
vo 1 ume to Lake Estes for the April-July peri od decreased to
70,000 acre-feet, which was 85 percent of average. The May forecast proved
, to be quite accurate as actual inflow for April-July was 69,400 acre-feet.

The maxim~m daily inflow of 968 ft3js occurred on June 12, and this was
114 perce~t of the 30-year average. June was extremely hot and dryas
precipitation was only 17 percent of average with 0.33 inches recorded;
the 8th lowest monthly total on record in 81 years. Natural inflows
decreased:to 158 ft3js by July 31: June and July inflows were 110 percent
and 84 petcent of average, respectively.

Due to thd low Adams Tunnel diversions and low irrigation deliveries, most
of the Big Thompson River inflow to Lake Estes was diverted (skimmed) for
power :f.ro~uction. Releases to the river below Olympus Dam peaked at
370 ft js pn June 13. Water diverted into Olympus Tunnel under operation
"skim" toltaled 42,809 acre-feet for the year and this resulted in
76 gigawat!t-hours of generation. This was 105 percent of the average
40,700 acr,e-feet annually diverted.

July and August precipitation at Lake Estes was much above normal at
189 percent of average and 141 percent of average, respectively. Total
precipitat~on for the water year (October-September) was 19.59 inches or
113 percent of average. The inflow above Lake Estes was 89,800 acre-feet
for water rear 1990 and this was 130 percent of average.

;
Estes Powe~plant generation totaled 95,600,000 kilowatt-hours for the water
ye~r and w4s 11,200,000 kilowatt-hours below average. This was due to the
below aver4ge Adams Tunnel diversions which were 92 percent of average. .

Carter Lake

Completed ip 1952 with three dams, Carter Lake has a total storage capacity
of 112,200 :acre-feet. Inflow of project water to Carter Lake is from the
Flatiron Pu~ping Plant with a capacity of about 400 ft3js.

Carter Lak$ storage content at the beginning of the water year was
36,450 acre~feet which was below the 30-year average of 51,000 acre-feet.
Project wat~r deliveries to the St. Vrain Canal continued through the end
of October and totaled 10,421 acre-feet for the month.. .

Continuous pumping to Carter Lake from Flatiron Reservoir continued until
mid-Octoberlto accommodate scheduled Charles Hansen Feeder Canal (550 ft3js
section) mafntenance during the October 1 to October 12 period. Pumping
to Carter Wake was shut down on October 19 due to the high del iveries
(400 ft3jS) ito the Big Thompson River and to have a deSirable inflow to
Horsetooth ~eservoir. Pumping began again on November 3 and continued
through Mardh 17 when Pole Hill Powerplant was shut down for maintenance.

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