WSP00886

• File Number: 8407
• Description: Platte River Basin - River Basin General Publications
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 4/16/1990
• Author: BOR
• Title: Annual Operating Plans - North Platte Project Water Years 1989-1990
• Water Supply Pro - Doc Type: Report/Study

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April inflows at 156 percent of average. Early runoff is common in dry
years.

Reservoir storage reached the year's low of 66,146 acre-feet on April 18
and April 20. A target storage of 60,000 acre-feet at the end of April
is desired for the most probable runoff condition, and 70,000 acre-feet
for the mi n imum runoff cond i t ion. May was warm and dry, with on ly 76
percent of aver~ge precipitation. Computed reservoir inflow increased
to near 1,200 ft~/s by the end of the month.

Dillon Reservoir filled to capacity on May 27 and started to spill
over the uncontrolled 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 acre-feet spilled in water year 1989. Dillon Reservoir ended
the water year at a storage level of 249,876 acre-feet.

Computed i nfl ow to Green Mountain Reservoi r peaked for the year at
1,754 ft3/s on June 17. Turbine releases averaged only 175 ft3/s during
June in order to increase reservoi r storage near to a phys i ca 1 fill
(154,645 acre-feet).

During July, turbine releases were regulated to attain the target
storage 1 eve 1 of 152,000 acre-feet, wh i ch fi 11 s the rep 1 acement pool
(52,000 acre-feet) and the power pool (100,000 AF). Turbine releases
averaged 340 ft3/s during July. Green Mountain Reservoir inflow
decreased to near 350 ft3/s by mid-July but increased to near 500 ft3/s
by the end of the month due to rainfall. Maximum reservoir storage was
152,201 acre-feet on Ju ly 18, 201 acre-feet above the target storage.
Actual Apri l-July runoff was 213,900 acre-feet, 80 percent of average,
and 104 percent of the May 1 forecast.

Release for natural flow Shortage was called for on the Colorado River
on Ju ly 19 when the flow at the Cameo gage dropped be 1 ow 2,260 ft3 /s.
Very low tributary inflow from the Fryingpan River resulted in the
earliest recorded call on the river at the Cameo gage. Turbine 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 natural-flow shortage, bypass of inflow, and CBT
Project replacement cont i nued from Green Mountai n Reservoi r for the
remainder of the water year, and, were as high as 953 ft3/s on
September 5. The recorded flow at Dotsero for the Colorado River was
1,042,100 acre-feet for water year 1989, which was only 68 percent of
average (exhibit 3).

The August and September inflows were below average at 87 percent and
80 percent, respectively. September was very dry at only 42 percent of
average preci pi tat ion. By the end of the water year. turbi ne releases
were high at 600 ft3/s and reservoir 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 average inflow of 371,000 acre-feet.
Blue River, Dillon Reservoir, and Green Mountain Reservoir operations
for water year 1989 are summarized in table 2.