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<br />001' Cl}') <br />. U __ v <br /> <br />at Hoover Dam. Table C-7 indicates 89 percent or 9,784,000 acre-feet <br />of the total specified release of 11,010,000 acre-feet will reach <br />Lake Mead. <br /> <br />The control zone volumes of Table IV are presented graphically in <br />Figure 4. They were chosen to roughly duplicate recent reservoir <br />fluctuations. They were also selected to operate Lakes Powell and <br />Mead in a "balanced" condition. However, they do not rigorously <br />duplicate the current operational criteria useQ for filling Lake <br />Powell. The latter criteria are based on an allocation of storage <br />concept as opposed to the allocation of releases to meet downstream <br />demands employed by the model. The former approach requires a <br />"look-ahead" or forecast capability to avoid erratic release pat- <br />terns resulting from an attempt to bring levels into balance at an <br />arbitrarily chosen time, such as October. <br /> <br />It should also be noted that requirements of a short-term operating <br />model are somewhat different from those for long-term planning or <br />overall operations. In the latter case, uncertainties involving <br />the impacts of new and unforeseen technology (desalting, geothermal, <br />fertilizers, improved systems understanding and operation), shifting <br />criteria for selecting projects for future development, and the <br />effects of rapidly changing social objectives can easily outweigh <br />current detailed operations. Thus, an excessive expenditure of <br />resources to develop rational criteria for operation of reservoirs <br />in the model may not yield commensurate returns in terms of model <br />confidence. <br /> <br />The recent court orders involving the controversy over filling Lake <br />Powell and encroachment of waters into the Rainbow Bridge National <br />Monument illustrates the impossibility of duplicating actual oper- <br />ations. As a consequence, rough, overall criteria are deemed ade- <br />quate for purposes of salinity projections. <br /> <br />Run Criteria <br /> <br />Certain criteria or assumptions were made which are common to all <br />runs. This was done to place individual analyses on a more-or-less <br />comparable basis. Without the assumptions, erroneous or misleading <br />conclusions could easily be drawn. <br /> <br />(1) Upstream boundary conditions - Upstream boundary inputs <br />can represent historic conditions, modifications of these, or <br />stochastically generated ones. However, for purposes of this <br />study, present modified data for the 1941-1970 period were used. <br />Nodes were added immediately downstream from each boundary to <br /> <br />19 <br />