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<br />fl'.. <br /> <br />" I.. .~ <br />"l :~.' <br /> <br />18 <br /> <br />Chapter 2.0 Description of Alternatives <br /> <br />Third, if at least 800,000 metric tons of sediment input are retained in the Colorado <br />River between Glen Canyon Dam and the Little Colorado River by January 1 of the <br />ensuing year, then a powerplant and jet tube total release between 42,000-45,000 cfs <br />would occur in the first week of January in an effort to "bank" the conserved sediment <br />at higher elevations within the Grand Canyon. This high flow would last for <br />approximately 60 hours. Upramp rates for this release would be 4,000 cfs/hour for the <br />first two hours, then 1,500 cfs/hour up to powerplant capacity, then opening one bypass <br />tube in two steps over the course of six hours until reaching jet tube capacity. The <br />downramp rate would be 1,500 cfs/hour from maximum releases (42,000-45,000 cfs) to <br />8,000 cfs and this would take about 22 hours to achieve. A steady release of 8,000 cfs <br />would be continued for a period not to exceed 10 days during which time aerial <br />photography and surveying would occur to document the effect of the high flow test on <br />sediment conservation and other resources. If the minimum sediment accumulation <br />does not occur by January 1, dam releases would change to fluctuating non-native fish <br />suppression releases between 5,000 cfs and 20,000 cfs with an upramp rate of 5,000 <br />cfs/hour and a downramp rate of 2,500 cfs/hour. The fluctuating non-native fish <br />suppression flows would continue from January through March unless a minimum <br />sediment input of 800,000 metric tons is received. <br /> <br />These fluctuating non-native fish suppression flows were designed to mimic pre- <br />1990 daily fluctuations and ramp rates. Pre-1990 flows limited natural recruitment of <br />rainbow and brown trout (Maddux et al. 1987). The proposed downramp rate of 2,500 <br />cfs/hour was also selected to test the validity of the beach seepage model used to <br />formulate the ROD downramp constraints. <br /> <br />If the minimum tributary sediment input of 800,000 metric tons occurs in the months <br />of January-March during fluctuating non-native fish suppression flows, <br />the winter sediment input scenario (figure 2.4) would begin with the release of 42,000- <br />45,000 cfs. This release would have the same features as the high flow test under the <br />autumn sediment input scenario, including the succeeding period of 8,000 cfs steady <br />releases for aerial photography and surveying. It would interrupt the non-native fish <br />suppression flows, but they would be resumed through the end of March following the <br />high flow test and ensuing steady releases. <br /> <br />The third hydrologic scenario is the no sediment input scenario (figure 2.5). In this <br />scenario, the minimum sediment inputs necessary to trigger the autumn sediment <br />scenario or the winter sediment input scenario do not occur. Under these conditions <br />ROD operations would continue until at least July 1 of that water year, except for the <br />January to March period of fluctuating non-native fish suppression flows. Dam releases <br />after July 1 would depend on tributary sediment inputs. If minimum tributary inputs <br />occur and the first scenario has been completed, the fourth hydrological scenario would <br />be initiated. If they do not occur, ROD operations would continue. <br />