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<br />exceeded about 70 percent of the time, This means that Lake Powell would <br />gain storage in the spring this frequeucy of years in the future. <br /> <br />c - Routings of average (1996). upper quartile ( 1993). and extreme (1983) years were <br />made to determine the duration of inundation at various levels upstream of the <br />dam, Starting conditions were assumed as an elevation of3500 feet and an ability <br />to pass inllow lip to the 45.000 cIs level. The following table shows the routing <br />results: <br /> <br />Year Type Max Inflow # Days of Max Elev <br /> (cfs) Elev > 3500 feet (feet) <br />1996 Average 56,039 8 3501.5 <br />1993 Upper Quartile 80.993 70 3521.7 <br />1983 Extreme 122.739 149 35678 <br /> <br />d - Topographic maps were examined to observe the etfect of both the drawdown to <br />elevation 3500 feet and the re-inundation of exposed areas as the result of not <br />being able to pass intlow to the lake, At full pool of 3700 feet elevation, Lake <br />Powell is about 186 miles in length. With implementation of the restriction of <br />elevation 3500 feet, our professional judgment indicates only about 20 miles <br />of upstream river channel would return to riverine conditions. This however <br />would allow the lower end of Cataract Canyon to again be utilized as a whitewater <br />area, This is far less than most would assume at first blush and results from <br />the steep gr:ldient of the upstre:lm reaches of the lake. Many of the side <br />canyons would be exposed away from the lake, so the 200 foot reduction in <br />lake level would have positive effect, but perhaps not to the degree that is <br />initially expected. The lake would be over 300 feet deep at the dam. Annual <br />peak inflows over the 45.000 cfs level would cause some impacts to recreational <br />use due to re-inundation, <br /> <br />e - A cross-section of the dam gives some feel to the relative positions of the various <br />plumbing fixtures, Since there is about 202 feet of elevation difference between <br />the original streambed level (elevation 3172 feet) and the hollow jet outlet works <br />(elevation 3374 feet). this entire depth must fill in with sediment in order to be able <br />to pass any of the sediment through the outlet tubes, With the limited exposure of <br />upstream channel, it is probable that future sediment deposition would continue to <br />occur at the upstream end of the lake, Bypassing of sediment through the dam <br />likely would not occur in the near future. <br /> <br />f - Strangely enough, system consumptive use impacts would be very similar to <br /> <br />8 <br />