|
<br />Actual Operations Under Criteria - Water year 1989
<br />
<br />The initial plan of operation for the water year ending
<br />September 30, 1989, called for scheduled releases from Lake
<br />Powell of 8.5 million acre-feet (mal), Based on the inflow
<br />forecast at the beginning of the year, this plan of operation
<br />would have created 7,1 mof of vacant space in the Colorado
<br />River reservoir system by the end of September 1989,
<br />
<br />The April through July forecast of runoff into Lake Powell
<br />made on January 1,1989, was 7,0 mof or 87 percent ofthelong
<br />term average, The long-term average is calculated by the
<br />Bureau of Reclamation using 80 years of natural flow data
<br />(1906-1985) and current depletion levels. Releases from Glen
<br />Canyon Powerplant averaged about 12,000 cubic feet per
<br />second (cfs) for January'through February, The monthly
<br />April-July forecasts decreased slightly for March, to 85
<br />percent of average. In response to this lower forecast,
<br />powerplant releases were decreased to 30 percent of capacity
<br />during March and April, The April 1 forecast dropped to 80
<br />percent of the long-term average or 6.5 mof for the April
<br />through July period. Precipitation continued to be below
<br />avcrage through Juoe and the forecast for April through July
<br />continued to drop, On June 1 the April through July forecast
<br />was 3.8 mof or 47 percent of average, Releases for the water
<br />year were set at 8.23 maf to meet minimum required releases
<br />to the lower basin states and Mexico,
<br />
<br />As in 1988, climatic conditions for water year 1989 were again
<br />dry, a result of the continued dry storm pattern's from the last
<br />few years, affecting much of the Upper Colorado River basin
<br />and surrounding areas, Precipitation for the water year was
<br />81 and 68 percent of average, over the Upper Colorado Basin
<br />and the Lower Colorado Basin, respectively, Ruooff over the
<br />Upper Colorado Basin was much below average, with actual
<br />
<br />unregulated April-July inflow to Lake Powell 013,5 maf or 43
<br />percent of the long-term average, Unregulated runoff is the
<br />inflow to Lake Powell adjusted for the change in storage of
<br />the upstream reservoirs discussed in this report. Lake Powell
<br />recorded a peak snowmelt inflow of 18,400 cfs on May 27, and
<br />reached a maximum elevation on J uoe 11, 1989, of 3.678,64
<br />feet, or 86,7 percent full.
<br />
<br />The total unregulated runoff into Lake Powell for the water
<br />year was 6,25 mof or 53 percent of the long-term average,
<br />Water supply for the San Juan River above Navajo Dam for
<br />the water year was 84 percent of the long-term average; the
<br />Gunnison River above Blue Mesa Dam was at61 percent; the
<br />mainstem Colorado River above Grand Junction, Colorado,
<br />65 percent; and the Green River above Flaming Gorge Dam,
<br />53 percent. Total releases from Glen Canyon Dam were 8,23
<br />mof while the regulated inflow for the year was 5,78 mal.
<br />Aggregate Colorado River storage at the end of the year was
<br />48,2 mof representing a decrease of 4,2 maf from the previous
<br />year,
<br />
<br />During water year 1989, Mexico received a total delivery of
<br />about 1,540,000 acre-feet at the Northerly International
<br />Boundary (NIB). Of the 1,540,000 acre-fect of
<br />Colorado River water reaching the NIB, about
<br />520,000 acre-feet were delivered through the Pilot Knob
<br />Powerplant and Wasteway from the All-American Canal. An
<br />estimated 440,000 acre-feet were released through
<br />Laguna Dam, The remainder of the flow at the NIB was made
<br />up of return flows to the Colorado River below Laguna Dam,
<br />and returns to the Gila River below the gaging station near
<br />Dome. as well as small Gila River releases from
<br />Painted Rock Reservoir,
<br />
<br />2
<br />
|