WSP00328

• File Number: 8027
• Description: Section D General Correspondence - Federal Agencies
• State: CO
• Basin: Statewide
• Date: 7/1/1971
• Author: DOI-BOR
• Title: Annual Operating Plan - Western Division - Pick-Sloan Missouri Basin Program - 1971-1972
• Water Supply Pro - Doc Type: Report/Study

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Eastern Slope - Colorado- Big Thompson Project

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Carryover storage in Carter Lake ancl Horsetooth Reservoirs totalled 168,000
acre-feet at the beginning of Water Year 1971. This was about 60,000 acre-feet
above the 10-year average. Delivery of irrigation water to project users con-
tinuecl throughout October . Total supplemental water deHvery for the 1970 season
was 150,000 acre-feet.

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Precipitation was nearly normal over the eastern slope areas through March. As
of April 1, snowpacks ranged from 100 to 125 percent of average. Private storage
reserves in the irrigated area wer.e virtually full. Considering the above normal
pri mary water supply, the Northern Colorado Water Conservancy District declared
a 60-percent allotment of project supplemental water for the season.

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Heavy precipitation on the order of 4 to 5 inches occurreclover much of the area
late in April. With good soil moisture conditions and excellent local water supply,
this virtually assured that there would be no appreciable demand for project sup-
plemental water until July. With good supply and limited demand, this, in turn,
virtually assured a spill of Lake Granby water.

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Diversion of water was continued until the latter part of May when Carter Lake
and Horsetooth Reservoirs were filled to near capacity. There was no diversion.
of water from the western slope thereafter until delivery of non-charge water was
made early inJuly. Operation Skim was effectively used to support power require-
ments until late June. Skim was curtailed during July and August to allow maxi-
mum conservation of project water.

Precipitation was generally deficient over the eastern slope area from May until
mid-September. Extremely hot weather persisted after the middle of June.
Denver, Colo. . recorded 11 days over 90 degrees and 9 consecutive days over 90
degrees during June, establishing a newall-time record. Heavy delivery of non-
charge water early in July relieved the spill situation at Lake Granby and was of
great benefit to power system control and stability. While snowmelt runoff was
well above normal on the Big Thompson River, skim was normal for the season,
46,000 acre-feet.

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An early season storm dumped 12 to 20 inches of snow over the eastern slope area
on September 17. This early storm caused great damage to trees and crops and
overhead utilities. Forage crops were hard-hit especially corn for silage.

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