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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />1999 WATER SUPPLY ASSUMPTIONS <br /> <br />For 1999 operations, three reservoir unregulated inflow scenarios were developed and analyzed <br />and are labeled as probable maximum, most probable, and probable minimum. The attached <br />graphs show these inflow scenarios and associated release patterns and end of month contents <br />for each reservoir. <br /> <br />Although there is considerable uncertainty associated with streamflow forecasts and reservoir <br />operating plans made a year in advance, these projections are valuable in analyzing possible <br />impacts on project uses and purposes. Till: most probahle inflow in water year 1999 is proiected <br />to be near normal. Therefore, the magnitude of inflows in each of the three inflow scenarios are <br />'near the historical upper decile, mean, and lower decile (I 0 p~rcent exceedance, 50 percent <br />exceedance, and 90 percent exceedance, respectively) for each reservoir for water year 1999. <br />The three inflow scenarios for Lake Powell are shown in Tables 2(a) and 2(b). <br /> <br />The volume of inflow resulting from these assumptions was used as input into Reclamation's <br />monthly reservoir simulation model. This model is used to plan reservoir operations for the <br />upcoming 24-month period. Projected water year 1999 inflow and October I, 1998 reservoir <br />storage conditions were used as input to this model and monthly releases were adjusted until <br />release and storage levels accomplished project purposes. <br /> <br />5 <br />