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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preCiPitation. By the end of the water year, turbine releases were high
at 500 ft,js and reservoir storage stood at a very low 78,927 acre-feet,
which was '48,373 acre-feet below average.

The total ,1990 water year inflow of 303,700 acre-feet was 66,700 acre-feet
below the )960-1989 average inflow of 370,400 acre-feet. Blue River, Dillon
Reservoiri and Green Mountain Reservoir operations for water year 1990 are
summarized in table 2.

Gross gendrat i on at the powerplant totaled 40,300,000 kil owatt-hours for
the wateriyear. This was 18,100,000 kilowatt-hours below average.

Willow Creek Reservoir

Completed 1n 1953, Willow Creek Reservoir has a total storage capacity of
10,600 acre-feet. The uncontrolled spillway, located at the left abutment,
has a capa~ity of 3,200 ft3js. The Willow Creek Feeder Canal begins at the
left abutm~nt with a capacity of 400 ft3js for pumping to Granby Reservoir.

Reservoir carryover storage coming into water year 1990 was
8,194 acrelfeet. This was below the 30-year average of 9,000 acre-feet.

During October and November, the reservoir was drawndown to near
7,200 acreifeet to provide storage space for winter inflows. The release
to the river for fishery habitat and for irrigation demands totaled
1,639 acre~feet, and 603 acre-feet was pumped to Lake Granby. The minimum
reservoir content for the water year was 7,207 acre-feet on November 8.
October-Ja~uary inflows were below normal at only 70 percent of average.
PrecipitaUon for the October-January period was below average at
70 percent 'of average. .

The Februa~y 1 snow-water content was only 58 percent of average, which
resulted in! an April-July runoff forecast of 35,000 acre-feet.

The March 1, snow-water content increased to 79 percent of average and the
April-July runoff forecast increased to 40,000 acre-feet.

March predpitation increased sharply to 205 percent of average with
2.52 inches, recorded. Duri ng the October through March peri od,
precipitatipn in the Willow Creek watershed averaged 98 percent of normal.
Snowpack water content for the Apri 1 1 measurement was 87 percent of
average. . The April-July snowmelt runoff forecast remained at
40,000 acretfeet or 80 percent of normal. Inflows were above average at
109 percent 'of normal during March. .

The natural1inflow increased steadily in April from 26 ft3js on April 1 to
119 ft3js o~ April 24. However, the total April inflow was below normal
at 83 perce~t of average. A total of 3,522 acre-feet was pumped to Lake
Granby duri1ng the month. April had above normal preci pi tat ion at
126 percent lof average, but the May 1 snowpack water content was only
51 percent pf average. The April-July runoff forecast remained at
40,0,00 acre-ifeet.

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