WSP00585

• File Number: 8282.600.10
• Description: Colorado River Operating Annual Reports
• Basin: Colorado Mainstem
• Date: 1/1/1986
• Author: USDOI/BOR
• Title: Operation of the Colorado River Basin 1986 Projected Operations 1987
• Water Supply Pro - Doc Type: Publication

Actual Operations Under Criteria - Water Year 1986

The initial plan of operation for water year ending September
30, 1986, based on forecasted inflow conditions for October
through January and average inflow conditions through the
rest of the water year 1986 called for scheduled releases from
Lake Powell of 11.5 million acre-feet (MAP). This plan of
operation would have created 6.7 MAF of vacant space in the
Colorado River reservoir system by the end of September
1986, of which 1.8 MAFwould have been in Lake Powell. With
this plan of operation Ihe conlents of Lakes Powell and Mead
would have been within 3,000 acre-feet of each other at the
end of September 1986.

The April through July forecast of runoff made on January 1,
1986, was 10.6 MAF or 130 percent of the long term average.
This long term average is, calculated by the Bureau of
Reclamation using 80 years of natural flow data (1906;1985)
and current depletion levels. Accordingly, releases from Glen
Canyon power plant were maintained at 20,000 cubic feel per
second (cfs) January and February. The April-July forecast
increased slightly in March, up to 135 percent of average. In
response to this higher forecast, powerplant releases
increased to 90 percent of capacity during March and April.
A cold, wet April provided an increase to the snowpack, so by
the first of May the runoff forecast had increased up to 12.6
MAF or 154 percent of the long term average. As a result, the
releases from Glen Canyon were increased to 100 percent of
capacity for both the powerplant and river outlet works.
Reservoir inflows remained above average during May, and
in conjunction with a wet weatner pattern, caused an early
melt of lower elevation snow. This caused the inflow to Lake
Powell to rise to 61,400 cfs in early May.

With warmer temperatures, a snowmelt runoff peak of
110,400 cfs unregulated flow was observed on June 9, 1986.
Unregulated runoff is the inflow to Lake Powell adjusted for

the change in storage of the upstream resen'oirs discussed in
this report. Corresponding with the passing of the peak inflow,
the river outlet works at Glen Canyon were closed while thc
powerplant remained at maximum releases through the end
of the month. The actual uoregulated April-July runoff into
Lake Powell was 12.5 MAP in 1986, or 153 percent of average,
and Lake Powell reached its maximum elevation of 3,700.02
feet on July 27.

The total unregulated runoff for water year 1986 at Lake
Powell was 18.2 MAF or 152 percent of the long-term average.
Water supply for the San Juan River above Navajo Dam and
the mainstem Colorado River above Grand Junction,
Colorado, for the water year were at 169 percent, while the
Gll1l11ison River above Blue Mesa Oam was at 131 percent,
and the Green River above Flaming Gorge Oam was at 184
percent of average. Total releases from Glen Canyon were
16.7 MAP, while the regulated inflow for the year was 17.8
MAF. Aggregate Colorado River storage at the end of the
year was 55.7 MAF, representing an increase of 100,000
acre-feet from the previous year.

Commencing in 1986 the operation of the Colorado River
Reservoir System was coordinated with Federal and Slate
interests through the Colorado River Management Task
Force. The task force is comprised of representatives from
each of the seven Basin States, the Upper Colorado River
Commission, International Boundary and Water
Commission, Western Area Power Administration, and the
, Bureau of Reclamation, and was implemented by Secretary of
the Interior Oonald P. Hodel. It represents a comprehensive
effort by the seven Colorado River BasinStates and numerous
Federal agencies and serves as a technical forum for re,solving
operational issues on the Colorado River.

2