WSP09032

• File Number: 8407
• Description: Platte River Basin - River Basin General Publications
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 2/27/1991
• Author: BOR
• Title: Annual Operating Plans - North Platte Project Water Years 1990-1991
• Water Supply Pro - Doc Type: Report/Study

Granbv Reservoir

Completed in 1950, the Granby Reservoir on the upper Colorado River
collects and stores most of the project water supply for the Project. The
reservoir stores the flow of the Colorado River as well as water pumped
from Willow Creek Reservoir. The reservoir has a total storage capacity
of 539,800 acre-feet. The spillway, located on the left abutment, is
controlled by two radial gates with a total release capacity of
11,500 ft3/s. Granby Pumping Plant has three units with a combined
installed capacity of 600 ft3/s.

I
I
I
:.
t
I
I
I
I
I
I
I
I
I
I
I
,
I,
I

Natural inflow averaged only 199 ft3/s in May and peaked at 373 ft3/S on
May 24. Total monthly inflow was only 55 percent of average. A total of
10,801 acre-feet was pumped to Lake Granby during May.

June precipitation was much below normal at 26 percent of average, and
natural inflow continued to be low at 67 percent of average. By the end
of June, inflow had decreased to 88 ft3/s. Precipitation was 128 percent
of average for July, but natural inflow remained low at 60 percent of
average. Inflow averaged a low 49 ft3/s for July. Total April-July inflow
was 31,500 acre-feet or 62 percent of average. Condit ions were dry in
August and September and by the end of the water year, natural inflow
averaged only 13 ft3/S. Water pumped to Lake Granby totaled 9,245 acre-feet
for June, and no water was pumped in July, August, and September.

No water in excess of downstream irrigation demands and minimum required
fish releases was bypassed during the year.

During water year 1990, a total of 24,171 acre-feet was pumped to Lake
Granby. Inflow to the reservoir during the water year totaled
38,600 acre-feet which was only 64 percent of average.

On September 30, the reservoir had 8,744 acre-feet of water in storage.

Reservoir carryover storage into water year 1990 was 301,182 acre-feet
which was 118,318 acre-feet below the 30-year average of 419,500 acre-feet.

January precipitation was much below normal at 39 percent of average and
reservoir inflow was 78 percent of average. October-January precipitation
was 75 percent of average and the October-January inflow was 73 percent of
average.

The required minimum reservoir release of 20 ft3/s for fish habitat was
maintained throughout the October-January period.

The February 1 snowpack water content was recorded at 74 percent of
average, resulting in a April-July runoff forecast of 165,000 acre-feet.
February was continued dry at 80 percent of normal precipitation, and
90 percent of average i nfl ow. The March 1 snowpack water content was
78 percent of average which sl ightly increased the April-July runoff
forecast to 170,000 acre-feet. Wet condi t ions occurred in March, as
precipitation was 205 percent of average. April 1 snowpack increased to

12