WSP10742

• File Number: 8282.600.10
• Description: Colorado River Operating Annual Reports
• Basin: Colorado Mainstem
• Date: 1/1/1991
• Author: USDOI/BOR
• Title: Operation of the Colorado River Basin 1991 Projected Operations 1992
• Water Supply Pro - Doc Type: Publication

Actual Operations Under Criteria - Water Year 1991

Climatic conditions in the Colorado River Basin for water
year 1991, as in 1988, 1989, and 1990 were dry. Precipitation
for the water ~ar 'WaS approximately 95 percent of average.
The:: extended drought, however, and the associated soil
moisture deficit caused spring runoff in the Upper Basin to
be considerablybelowawra8c. Unregulated April,Julyinflow
to Lake Powell was 5,286,000 acre-feet, 65 percent of the
long-term awrage. U nrcgulatcd runoff is the inflow to Lake
Powell adjusted for the change in storage of the upstream
reservoirs. Lake Powell recorded a peak regulated inflow of
38,000 eubic feet per second on June 17, 1991. The total
unregulated runoff into Lake Powell for the water year was
8,385,000 acre-feet, 70 percent of the long-term average.

All of the Upper Basin resenolrs recorded below normal
inflows in waler year 1991. San Juan River inflow to Navajo
Reservoir was 98 percent of the long-term average.
Unregulated inflow of the Gunnison River to Blue Mesa
Reservoir was 78 percent of normal, while- unregulated inflow
of the Green River to Flaming Gorge Reservoir was 80
percent of the long-term average. Inflow to Fontenelle
Reservoir from April through July was 82 percent of
norma 1.

Upper Basin rescrvoirs~ Flaming Gorge, Blue Mesa, and
Navajo. experienced modest rebounds in storage in \.Vater year
1991. Storage in Lake Poweli and Lake Mead, however, is
down 1.0 and 1.4 million acre-feet. respectively. The October
1,1991, Colorado River system vacant space was 18.6 million
acre-feet. Aggregate Colorado River live storage at the end
of the year was 42.2 million acre-feet. Aggregate storage
decreased in water year 199! by 1.7 million acrc,fcet.

Total releases from Glen Canyon Dam (detiwrics from the
Upper Basin to the Lower Basin) for water year 1991 were
8.23 million acrc,fcet. The 1991 operation plan allowed the
water needs of the Lower Basin states to be satisfied, up to 7.5
million acre-feet of beneficial consumptive use, during the
calendar year.

During water year 1991. Mexico received a total delivery of
about 1,390,CX>O acre-feet at the Northerly International
Boundary (NIB), Of the 1,390,000 acre-feet of
Colorado River water reaching the NIB, about
506,000 acrc-fcet wcre deti""red through the Pilot Knob
Powerplant and Wasteway from the AIl~American Canal. An
esti.mated 303,000 acre-feet were released through
Laguna Dam. The remainder of the flow at the NIB was made
up of return floVIIS to the Colorado River below Laguna Dam.

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