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<br />01247 . <br /> <br />c <br /> <br />D-R-A-F-T <br /> <br />P:\User\Thomas\95Rate\Pwrpnt I.wpl <br /> <br />May 12. 1993 <br /> <br />operational changes is a flow regime called beach/habitat-building flows <br />(BHBF).' The water needed for both flows could be retained from use during <br />other months in the year, or it could be produced by storage-equalization <br />re 1 eases. As wi th the Fl ami ng Gorge operat ions, the shi ft in water <br />releases would result in a shift in energy generation. <br /> <br />Additional focus <br />flood releases. <br />Releases.' <br /> <br />at Glen Canyon Dam concerns the downstream effects of <br />Unscheduled releases are considered Damaging Flood <br /> <br />The GCD-EIS team has recommended that Reclamation limit Glen Canyon Dam <br />releases to no more than 40,000 cfs at any given time, except during <br />beach-building periods. Proposed methodologies of managing flood releases <br />include careful statistical planning of reservoir storage and releases, <br />additional flood control storage space, and a structural modification of <br />the Glen Canyon Dam spillway gates in which splash boards would be <br />installed. Reclamation bel ieves that no change in the Long Range <br />Operating Criteria for Glen Canyon Dam would be implemented as a result of <br />any of these methods of managing flood releases, since the mandate to <br />avoid spills is contained in P.L. 90-537. <br /> <br />( <br /> <br />. <br /> <br />Proposed operational changes at the Aspinall Units are not yet known with <br />any certainty. As with Fl aming Gorge, a natural hydrograph may be <br />mimicked with Crystal Dam releases, shifting water releases from the <br /> <br />every year the reservoir is low. The HMF would not occur in years <br />when a BHBF is scheduled. <br /> <br />2 <br /> <br />High steady releases at least 10,000 cfs greater than the allowable <br />peak discharge in a minimum release year for a given alternative, <br />but not greater than 45,000 cfs for one to two weeks in the spring, <br />to coincide with the natural hydrologic cycle or late summer when <br />local thunderstorms increase sediment input from the tributaries. <br />For purposes of impact analyses, the BHBF were assumed to be steady <br />at 10,000 cfs greater than the allowable peak discharge in a minimum <br />release year for a given alternative, but not greater than 45,000 <br />cfs for ten days in March. The BHBF would occur in years when the <br />projected storage in lake Powell on January 1 is less than 19 MAF <br />and sufficient quantities of sediment are available, approximately <br />two in five years. <br /> <br />Unscheduled releases greater than 40,000 cfs (not including the <br />BHBF, because they are scheduled. Flood frequency reduction <br />measures were designed and included in the GCD-EIS to eliminate or <br />minimize these unscheduled releases. <br /> <br />I . <br />\. <br />'.. <br /> <br />2 <br />