WSP12907

• File Number: 8441.700
• Description: Colorado Big Thompson
• State: CO
• Basin: South Platte
• Date: 1/1/1997
• Author: USDOI/BOR
• Title: Annual Operting Plans Colorado Big Thompson Project & Western Division Systems Power Operations, Water Year 1997 Summary of Actual Operations
• Water Supply Pro - Doc Type: Annual Report

SUMMARY OF 1997 OPERATIONS

Water year 1997 runoff was slightly below average throughout the Colorado-Big Thompson Project
(Project) varying from 73 percent of average for the inflow into Willow Creek Reservoir to 119
percent of average for the inflow into Lake Estes.

Peak inflows into reservoirs within the Project, although higher than average, did not have a major
impact on the storage volumes. The months of May and June produced the highest runoff, with
June recording the highest total volumes. Lake Granby peaked at 2,360 ft3/s on May 22, and
Willow Creek Reservoir at 1,425 ft3/S on May 23, while Green Mountain Reservoir peaked on June
20 at 3,390 fe/s and Lake Estes peaked ~n June 5 at 1,110 fe/so

The maximum release at Green Mountain Reservoir was 1,724 ft3/S on June 25. A total volume of
46,189 acre-feet was spilled at Green Mountain Reservoir in the water year 1997. Further
upstream, along the Upper Colorado Basin, river releases from Willow Creek Reservoir were
higher than the 30-year average for most of the water year. Meanwhile, Lake Granby maintained
the minimum required releases. Regardless of the lower releases from Lake Granby, minimum
flow requirements for fish habitat were met throughout the year. Willow Creek Reservoir and Lake
Granby spilled 82,900 acre-feet and 68,200 acre-feet respectively during water year 1997, the third
largest volume in 50 years for each reservoir. The river release at Willow Creek Reservoir peaked
at 1,301 ft3/s on May 23, and the river release from Lake Granby peaked at 2,069 ft3/S for a daily
average on June 12. The peak flow of 2,100 ft3/S was observed on June 12 at the YMCA ~age. The
maximum flow observed at the Big Thompson River Gage below Lake Estes was 1,066 fr /s on
June 2. Project water deliveries peaked on May 11 at Horsetooth Reservoir with 1,219 ft3/S and at
Carter Lake on July 11 with 535 ft3/S. The maximum Project delivery to the Big Thompson River
occurred between May 11 and May 16, when a flow of 500 fr3/s was discharged.

Water year 1997 precipitation totals for October-September were well above average for the region.
The percentages of average ranged from 124 percent for the Green Mountain watershed to 155
percent for the Poudre watershed based on six rainfall stations.

Winter precipitation on the Project for the period of October to January was 144 percent of average,
with January recording significant accumulations. The western slope stations reported most of the
precipitation, with 153 percent of average for the first four months of the water year. Green
Mountain Dam received 2.08 inches of precipitation during January, which was 115 percent of
average. The eastern slope stations reported 131 percent of average precipitation. During January,
the Lake Estes and St. V rain watersheds received 1.52 inches of precipitation, which was 238
percent of average. Snowpack totals were 156 percent of average for the Upper Colorado Basin
and the South Platte Basin by January 3, 1997. Snowpack water content on February 1 was also
well above average, with 163 percent of average across the Project region. The highest snow pack
water content was found at the Willow Creek Reservoir watershed with 179 percent.

Temperatures along the eastern slope were warmer then normal during early January. High
temperature records were broken in nine different cities across Colorado on January 2, 1997. The
City of Fort Collins tied the old record of 630F set in 1918.