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<br />1996 Average 56,039 8 3501.5 <br />1993 Upper Quartile 80,993 70 3521.7 <br />1983 Extreme 122,739 149 3567,8 <br /> <br />d - Topographic maps were examined to observe the effect 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 inflow to the lake, At full pool of3700 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 of <br />upstream river channel would return to riverine conditions, This however would <br />allow the lower end of Cataract Canyon to again be utilized as a whitewater area, <br />This is far less than most would assume at first blush and results from the steep <br />gradient of the upstream reaches of the lake, Many of the side canyons would be <br />exposed away from the lake, so the 200 foot reduction in lake level would have <br />positive effect, but perhaps not to the degree that is initially expected, The lake <br />would be over 300 feet deep at the dam, Annual peak intlows over the 45,000 cfs <br />level would cause some impacts to recreational use due to re-inundation, <br /> <br />e - A cross-section of the dam is attached to give some feel to the relative positions of <br />the various plumbing fIXtures, Since there is about 202 feet of elevation difference <br />between the original streambed level (elevation 3172 feet) and the hollow jet outlet <br />works (elevation 3374 feet), this entire depth must fill in with sediment in order to <br />be able to pass any of the sediment through the outlet tubes, With the limited <br />exposure of upstream channel, it is probable that future sediment deposition would <br />continue to occur at the upstream end of the lake, Bypassing of sediment through <br />the dam likely would not occur in the near future, <br /> <br />f - Strangely enough, system consumptive use impacts would be very similar to <br />completely emptying Lake Powell, since there would be no storage that could be <br />released during drought periods, only temporary storage during the ronoff season <br />which would then be evacuated when inflows dropped, Under the assumption that <br />elevation 3500 would be viewed as a type of minimum pool, annual releases to the <br />lower basin would be about the same as the full evacuation alternative, <br />Evaporation at Lake Powell would be reduced from current levels by about two- <br />thirds, but evaporation at Lake Mead would increase slightly due to a higher long- <br />term lake level. If some drawdown below elevation 3500 feet were permitted to <br />control high ronoffyears, this would eliminate months of power generation <br />capability but would reduce the re-inundation of canyon reaches upstream, <br /> <br />g - This concept could result in greater contlict between lake and downstream river <br />interests, since both resources could be significantly compromised from current <br /> <br />4 <br />