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<br />Projected Plan
<br />
<br />In addition to compliance vlith the Operating Criteria, several
<br />specific operating issues were addressed during the
<br />preparation ofthe annual operating plan for water year 1992.
<br />Consideration 'WaS given to the dry condition of the basin, the
<br />vacant rescrmir space that currently exists, req uests for '\Vater
<br />by holders of water delivery contracts with the United States,
<br />and other tights recognized in Arimna \IS. California. The
<br />operaling issues addressed whieh are listed in no particular
<br />ordcr of priority are: (I) meeting the reasonable beneficial
<br />Colorado R i\et mainstream consumptive water uses in the
<br />Lo'WCt Division States as provided by the Operating Criteria,
<br />(2) the delivery of rum power in accordance with cncrgy
<br />contracts, (3) minimum and specific releases for fish and
<br />wildlife and recreational purposes, (4) refilling of vacant
<br />system reservoir storage space, (5) potential for flood control
<br />releases in years before shortages may occur, (6) water
<br />wasted to the GulfofCalifornia, (7) compliance with the 1944
<br />Mexican Water Treaty and Minute No. 242 of the IBWC, (8)
<br />the use of allocated but yet undeveloped in the Upper Basin,
<br />and in Arizona, and Nevada ofthc Lower Basin, (9) the ability
<br />to store unused water apportionments, (10) guidelines for
<br />reservoir filling and drawdown recommended for fish
<br />spav.ning periods in Lake Mead, (11) complying fully wilh
<br />compact, decree, statutory, and water delivery obligati.ons,
<br />and (12) olher short- and long,tcrm effects of 1992 water use
<br />decisions.
<br />
<br />For 1992 operations, three reservoir inOow scenarios were
<br />developed and analyzed. The projeclcd monthly inflow.;
<br />wete based upon cuttent hydrological coooitions &nd the
<br />following assumptions: (I) probable maximum, based upon
<br />the annual volume of inflow which would be exceeded about
<br />10 pctcent oflhc time, (2) most probable, based upon annuai
<br />volume of inflow which would be exceeded about 50 percent
<br />of the time; and, (3) probable minimum, based upon the
<br />annual ",lume ofinflow which would be clOCeeded about 90
<br />percent of the time. Each scenario \1135 adjusted for current
<br />basin conditions; therefore, the magnitude of the three
<br />scenarios does not necessarily match the historical upper
<br />decile, mean, and lower decile inflows, respecti~ly. The
<br />National Weather Service's computer model, knov.n as the
<br />Extended Streamflow Prediction model (ESP), uses cuttcnt
<br />
<br />basin conditions as well as historical data to predict a range
<br />of possible future s!ream flow.;. A Ithough there is a wide
<br />confidence band associated with stream flow forecasts tnade
<br />a year in advance, the data are wluable in analyzing the
<br />possible impacts on project uses and purposes. The inflow
<br />mlumes resulting from these assumptions were used as input
<br />data in Reclamation's monthly reservoir operation planning
<br />computer model, which is used to plan reservoir operations
<br />for the upcoming 12,month period. With assumed water year
<br />1992 inflow and current reservoir storage conditions,
<br />projected monthly releases were adjusted until release and
<br />storage levels accomplished project purposes and priorities.
<br />
<br />Special long-range studies using Reclamation's Colorado
<br />River Simulalion System (CRSS) were conducted to
<br />determine whether sufficient quantities of mainstream 'h'3ter
<br />were available for release from Lake Mead fo satisfy
<br />reasonable beneficial consumpti~ use requests in excess of
<br />7,500,000 acrc,fcct in the Lower Division Slales. The studies
<br />were conducted using the entire hydrologic record (1906
<br />through 1990), utilizing 85 hydlOlogic sequences indexed by
<br />one year. These; studies simulated operations 30 years into the
<br />future to assess the risks of shortages fa all users of Colorado
<br />River water for beneficial purposes and evaluated se.....eral
<br />specific parameters.
<br />
<br />At several locations in both Uppct and Lower Basins,
<br />minimum instrcam flows have been established in order to
<br />preserve the present aquatic resources dO\\11stream of certain
<br />Colorado River dams. In many cases, these resources were
<br />poor or nonexistent prior fa fhe time of dam construction, and
<br />the subsequent controlled, cool water releases have provided
<br />an improved environment for aquatic rcwurces. and spott
<br />fisheries. However these releases are believed to be
<br />detrimental to endangered endemic species of fish. In 1992,
<br />studies on the Green Riyer will continue, studies on the
<br />Gunnison and San Juan Rivers will be initiated in order to
<br />bener understand the water needs of the endangered endemic
<br />species of fish in the basin. In general, controlled releases
<br />allow for an extended recreation season, reduce the high flow
<br />periods, and improve sport fisheries, but may be detrimental
<br />to endemic species of fish.
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