WSP03460

• File Number: 8441.700
• Description: Colorado Big Thompson Project - Annual Operating Plans
• Basin: South Platte
• Water Division: 1
• Date: 1/1/1989
• Title: Annual Operating Plans - Colorado Big Thompson Project - Water Year 1989-1990
• Water Supply Pro - Doc Type: Report/Study

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Apr-i 1 inflows at 156 percent of aver-age. Ear-ly r-unoff is common in dry
years.

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Reser-voir storage r-eached the year-'s low of 66,146 acr-e-feet on April 18
and April 20. A target storage of 60,000 acr-e-feet at the end of April
is desir-ed for- the most pr-obable r-unoff condition, and 70,000 acr-e-feet
for- the minimum runoff condition. May was warm and dr-y, with only 76
per-cent of average precipitation. Computed reservoir inflow increased
to near- 1,200 ftJ/s by the end of the month.

Di 11 on Reservoi r- fi 11 ed to capacity on May 27 and star-ted to spi 11
over the uncontr-olled spillway on May 28. Spill at Dillon reached a
maximum of 874 ft3/s by June 18. The spill ended on July 4 for- a total
of 34,384 acr-e-feet spilled in water- year- 1989. Dillon Reservoir- ended
the water year at a storage level of 249,876 acre-feet.

Computed inflow to Green I~ountain Reseryoir- peaked for the year- at
1,754 ft3/s on June 17. Tur-bine releases aver-aged only 175 ft3/s dur-ing
June in order- to increase reservoir- storage near to a physical fill
(154,645 acr-e-feet).

Dur-ing July, turbine r-eleases were r-egulated to attain the target
stor-age level of 152,000 acre-feet, which fills the r-eplacement pool
(52,000 acre-feet) and the power pool (100,000 AF). Turbine r-eleases
averaged 340 ft3/s dur-ing July. Green Mountain Reservoir inflow
decr-eased to near- 350 ft3/s by mid-July but increased to near- 500 ft3/s
by the end of the month due to r-ainfall. Maximum reser-voir- stor-age was
152,201 acr-e-feet on July 18, 201 acre-feet above the target storage.
Actual Apr-il-July runoff was 213,900 acr-e-feet, 80 percent of average,
and 104 per-cent of the May 1 forecast.

Release for- natural flow shor-tage was called for- on the Colorado River-
on July 19 when the flow at the Cameo gage dropped below 2,260 ft3/s.
Very low tr-ibutary inflow fr-om the Fryingpan River- r-esulted in the
ear-liest recor-ded call on the river at the Cameo gage. Tur-bine releases
were increased to approximately 360 ft3/s by the end of the month to
meet the Cameo call. Due to the very dry conditions along the Colorado
River, releases for- natur-al-flow shor-tage, bypass of inflow, and CBT
Pr-oject replacement continued fr-om Gr-een Mountain Reser-voir- for the
remainder of the water year-, and were as high as 953 ft3/s on
September 5. The recor-ded flow at Dotsero for the Color-ado River- was
1,042,100 acr-e-feet for water year- 1989, whi ch was on ly 68 percent of
average (exhibit 3).

The August and September- inflows were below average at 87 percent and
80 percent, r-espectively. September- was very dr-y at only 42 per-cent of
average precipitation. By the end of the water- year, tur-bine releases
wer-e high at 600 ft3/s and reser-voir- storage stood at a very low
97,985 acre-feet, which was 30,415 acre-feet below average.

The total 1989 water- year- inflow of 302,200 acre-feet was
68,800 acre-feet below the 1959-1988 aver-age inflow of 371,000 acre-feet.
Blue River-, Dillon Reser-voir, and Green Mountain Reser-voir oper-ations
for water- year- 1989 ar-e summar-ized in table 2.

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