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<br />downstream side of the structure. <br />Rock lining of beaches would help <br />prevent beach erosion from high <br />water velocities, recreational <br />activity, and fluctuation flows. The <br />work would consist of native rock <br />or vegetation and would be <br />designed to blend with the natural <br />environment. Rock would not be <br />taken from the river banks or <br />canyon walls, but would be taken <br />from the mouths of tributaries <br />(debris fans) in the Canyon. These <br />beach protection devices would be <br />constructed by hand or with small <br />mechanized equipment. Specific <br />beaches targeted for protection <br />would be identified by the National <br />Park Service (NPS). <br /> <br />The Hig/1 Fluctuation alternative <br />limits daily fluctuations to ~ 75 <br />percent of the mean daily flow, not <br />to exceed an 18,000 cis change per <br />day. The average about which the <br />fluctuation occurs could change by <br />15 percent. Ramping rates would <br /> <br />be limited to 6,000 cis per hour and <br />minimum releases would be 5,000 <br />cis year round. <br /> <br />The high fluctuation alternative <br />includes a single episode of sand <br />pumping to immediately restore <br />selected beaches. To compensate <br />for large daily fluctuations, a small <br />reregulation dam is part of this <br />alternative. Sand pumping is not <br />needed in this alternative due to the <br />near-steady releases from the <br />reregulation dam. <br /> <br />Reregulation Dam <br /> <br />Daily fluctuations could be <br />partially reregulated and affect of <br />the rate of change reduced by a <br />small dam downstream of Glen <br />Canyon Dam. This would provide <br />nearly steady flows, on a daily <br />basis, in Grand Canyon. One <br />potential reregulation dam site is <br />approximately one-half mile <br />upstream of Lees Ferry. Access for <br />boat launching upstream of the <br /> <br />dam and a fish ladder are planned. <br />The design would avoid increasing <br />water surface elevations (tailwater) <br />at Glen Canyon Dam. Powerplant <br />facilities are not proposed for the <br />reregulation dam. <br /> <br />Several different dam heights will <br />be evaluated. These could regulate <br />fluctuating flows to near steady <br />flows up to 87 percent of the time, <br />or could completely convert to a <br />steady flow essentially all flows, <br />including daily fluctuations which <br />rarely, if ever, occur. If a <br />reregulation dam allowed the river <br />flow downstream to fluctuate from <br />8,900 cis to 13,900 cis ( a 5,000 cis <br />change) the resulting change in <br />river level at Lees Ferry would be <br />less than 1.2 feet. Although flows <br />downstream from a reregulation <br />dam could be moderated, <br />fluctuation between Glen Canyon <br />Dam and the reregulation dam <br />would be magnified. <br /> <br /> SUMMARY OF ACTUAL RELEASE PATTERNS FROM <br /> GLEN CANYON DAM -1963 THROUGH 1988 <br /> Median Percent of Percent of Median Median <br /> Daily Time Time Minimum Maximum <br /> Fluctuations Fluctuations Releases Release (cfs) Release (cis) <br /> (cfs) Greater than Less Than <br /> 20 000 cis 3 000 cfs <br />Snrina lAnr\ 11.000 3 10 6.000 20.000 <br />Summer 16,000 25 7 5,000 25,000 . <br />I Aua\ <br />Fall. Oct\ 12 000 8 18 3.000 17.000 <br />Winter lFeb\ 13.000 10 10 4.000 19 000 <br /> <br />Median: Exceeded 50 percent of the time <br /> <br />Figure 5 - Summary of Actual Release Patterns <br /> <br />12 <br />