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<br />fir . :;49 <br />u~ .~'" <br /> <br />. <br /> <br />. <br /> <br />In this last review, nine alternatives were evaluated, <br />each one of which was set up to favor, in turn, a different <br />one of the authorized Hoover Dam project purposes of flood <br />control and river regulation, water conservation, and power <br />generation; which are listed here in descending order of <br />priority as established by Congress. Frequently, the optimum <br />operating procedure for one purpose is directly opposed to <br />the optimum operating procedure for another purpose. Flood <br />control benefits are maximized by keeping reservoir storage <br />levels low to maximize the amount of empty space available to <br />regulate flood flows. Water supply benefits are maximized by <br />keeping the reservoir storage levels high so as to provide <br />for deliveries during multi-year periods with low runoff. <br />Hydroelectric benefits are maximized by storage somewhat <br />lower than the optimum for water conservation so as to <br />minimize releases in excess of power plant capacity. Also, <br />such a lower storage level avoids the necessity to release <br />water to produce energy on a continuous basis rather than <br />storing it for release at a later time to meet peak power <br />demands. <br /> <br />Hydrologic analyses of the Colorado River system using <br />these alternatives were made jointly by the Corps of <br />Engineers and the Bureau of Reclamation, and the benefits of <br />each, as measured by reduced flood damages, increased <br />availability of water and generation of hydroelectric energy, <br />were compared. In addition, the impacts of these <br />alternatives on fish and wildlife, water quality, and other <br />parameters were analyzed. <br /> <br />The Corps of Engineers' analyses concluded that the <br />alternative that most closely paralleled the then-existing <br />regulations produced the optimum combination of beneficial <br />objectives. After public review and comments on the Corps of <br />Engineers' study, this alternative was adopted to form the <br />Hoover Dam Flood Control Regulations. <br /> <br />The regulations provide for (1) a minimum of 5,350,000 <br />acre-feet of empty reservoir space to be available as of <br />January 1 of each year, (2) forecasts to be made monthly, <br />from January through July, of the maximum inflow to Lake Mead <br />dur ing the per iod January through July of each year, and (3) <br />flood releases to be made based upon the current amount of <br />empty reservoir space and the forecasted Lake Mead inflow. <br />The required flood control releases are made in stepped <br />amounts, with the next-to-last step being the target maximum <br />rate of 40,000 cfs. This target maximum rate of release has <br />a 50-year history, having been determined for the initial. <br />operating plans for Hoover Dam and later by the Corps in its <br />earlier operating studies to be the maximum release rate from <br />Hoover Dam that "...would have caused only minimal damage <br />'downstream" . <br /> <br />-4- <br />