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<br />Projected Plan
<br />
<br />The 1990 operation plan reflects the effects of below average
<br />reservoir inIIow during 1988 and 1989, However, recognizing
<br />the system storage that is available and the beneficial water
<br />needs of the basin states, all requests for Colorado River water
<br />by holders of water delivery contracts with the United States,
<br />and of other water rights recognized by the decree in Arizona
<br />v, California, will be satisfied during calendar year 1990,
<br />
<br />A proposed operation plan for water year 1990 for major
<br />reservoirs of the Colorado River system was formulated and
<br />distributed to representatives of the Colorado River Basin
<br />States in November 1989, This plan was prepared in
<br />accordance with the Operating Criteria published June 4,
<br />1970, in compliance with Section 602, Public Law 90-537. The
<br />plan reflects operation for flood control, river regulation,
<br />beneficial consumptive uscs, hydroelectric power generation,
<br />water quality control, enhancement of fish and wildlife.
<br />recreation, and Colorado River Compact requirements,
<br />
<br />The Colorado River Basin has experienced below normal
<br />precipitation for the last few years resulting in depleted
<br />reservoir storage, very dry soil moisture conditions, lowering
<br />water tables, and below normal streamflows, Because of these
<br />conditions the operation plan for water year 1990 emphasizes
<br />the conservation of reservoir storage by providing minimum
<br />releases from Colorado River Basin reselVoirs.
<br />
<br />For 1990 operations, three reservoir inflow scenarios were
<br />developed and analyzed, Tbe projected monthly inflows were
<br />based upon current hydrological conditions and the following
<br />assumptions: (1) reasonahle maximum, based upon the
<br />annual volume of inflow which would be exceeded about 10
<br />percent of the time. (2) most probable, based upon annual
<br />volume of inflow which would be exceeded about 50 percent
<br />of the time; and (3) reasonable minimum, based upon the
<br />annual volume of inflow which would be exceeded about 90
<br />percent of the time, Each of these scenarios was adjusted for
<br />current soil moisture deficiencies throughout the basin;
<br />therefore, each is lower in magnitude than the historical upper
<br />decile, mean, and lower decile inflows, The National Weather
<br />Service computer model used to adjust the scenarios was the
<br />
<br />Extended Streamflow Prediction model. This model
<br />calculated the projected unregulated inflows for water year
<br />1990 above Lake Powell as 13,328,000, 9,009,000, and
<br />5,854,000 acre-feet for the three scenarios, respectively,
<br />
<br />The plan for water year 1990 calls for a total Glen Canyon
<br />release of 8,23 mof under all three assumed inflow conditions,
<br />Hoover Dam releases (including pumping from Lake Mead)
<br />will be sufficient to satisfy up to 7,500,000 acre-feet of
<br />reasonable beneficial consumptive use requirements by
<br />mainstream users in the Lower Basin during calendar year
<br />1990 in accordance with Article III of the Operating Criteria
<br />and Article II(B)(I) of the Decree in Ari70na v, California
<br />Because Arizona and Nevada will not fully consume their
<br />respective apportionments pursuant to Article Il(B)(I).
<br />California will be allowed to utilize apportioned but unused
<br />water from these States. provided that the calendar year 1990
<br />consumptive use by mainstream Lower Basin users does not
<br />exceed 7,500,000 acre-feet in accordance with Article I1(B) of
<br />the decree in Ari70na v. California.
<br />
<br />Because of the large vacant storage space in the Colorado
<br />River system reservoirs at the beginning of water year 1990,
<br />no flood control releases are anticipated from Hoover Dam
<br />pursuant to the Hoover Dam Flood Control Regulations, and
<br />no releases are contemplated from Glen Canyon Dam to
<br />avoid anticipated spills or to equalize active storage in Lakes
<br />Mead and Powell. Water releases from each of the Colorado
<br />River system reservoirs will be in accordance with existing
<br />minimum flow, reservoir operating criteria, target storage
<br />elevations, and, with the exception of Fontenelle, all releases
<br />will pass through the powerplants, The resulting operation
<br />will provide benefits to all the authorized project purposes at
<br />each of the reservoirs,
<br />
<br />The projected operation for most probable runoff conditions
<br />for the major reservoirs in the Colorado River Basin for water
<br />year 1990 is described in the following pages. Charts showing
<br />the projected monthly outflows from each reservoir for the
<br />three assumed hydrologic conditions are presented with each
<br />reservoir operation.
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