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<br />. <br /> <br />. <br /> <br />. <br /> <br />0022~8 <br /> <br />in-one hundred <br />long run. If <br />necessary to <br />boundaries. <br /> <br />year river <br />this were <br />consider <br /> <br />flow than would be expected in the <br />found to be the case, it may be <br />short term and long term floodway <br /> <br />There are Bl years of historic records on river flows <br />and records of dam operations dating from initial operations. <br />Early in the evaluation process, a comparative analysis was <br />made of the magnitude of the one-in-one hundred year river <br />release from Davis Dam that might occur in the next five <br />years versus what might be expected any time in the future. <br />The long period of record provided a good basis for <br />evaluation. The process of "stepped" releases, as <br />established in the Hoover Dam Flood Control Regulations, <br />provides for a major stepped release rate of 35,000 cfs. The <br />analysis conducted for this study indicated that a 35,000 <br />cfs release rate will control a range of snow melt runoff <br />events such that a maximum release of 35,000 cfs represents a <br />broad range of frequency events from less than one-in-one <br />hundred year to nearly a one-in-two hundred year event. The <br />primary difference is the duration of the 35,000 cfs release. <br />The difference in release rates for the short term versus the <br />long term was only approximately five percent, thus, it was <br />not deemed necessary to develop short and long term Floodway <br />boundaries. <br /> <br />RECOMMENDATION <br /> <br />The Task Force recommends the use of the methodology as <br />adopted in the previously referenced Methodology report to <br />determine the appropriate reservoir release rate without <br />special consideration of current reservoir conditions or <br />short-term Floodway boundaries. In the event that long term <br />conditions differ significantly from the current study <br />assumptions, an appropriate reevaluation will be made in the <br />five-year review process. <br /> <br />III. <br /> <br />ISSUE <br /> <br />with <br />year <br /> <br />Develop a procedure to combine the mainstream releases <br />the tributary flows to establish the one-in-one hundred <br />flow in the river below the confluence with a tributary. <br /> <br />DISCUSSION <br /> <br />A range of monthly flow duration curves consisting of <br />the probability of occurrence and the maximum flow rate was <br />relatively easy to establish for the river flow resulting <br />from Hoover Dam releases. A similar determination of the <br /> <br />V-3 <br />