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2 - With respect to the Glen Canyon Institute's concept to drain Lake Powell to elevation 3500 feet, the following can be noted: a - The minimum power pool elevation at Glen Canyon Dam is elevation 3490 feet. It is possible that some power production could occur at this elevation but there would be the possibility of a vortex, since the centerline of the powerplant penstock is 3470 feet. As shown on the attached reservoir capacity allocation sheet, the lake has a total volume of5,9 MAF at this elevation, From our area- elevation curves, the lake has an area ofabout 52,000 acres, 32 percent of the maximum area of 161,000 acres. b - The release capacity of the outlet works is about 15,000 cfs with a gate opening of about 60 percent at the full pool elevation of 3 700 feet. While this amount ldlIl be released at elevation 3500 feet, a gate opening of 100 percent is required to achieve this release, This may be questionable from a maintenance point of view since at 100 percent gate, the velocities in the outlet tubes currently causes severe cavitation, If restricted to 60 percent gate, the capacity at elevation 3500 feet is about 11,600 cfs, Powerplant release capacity is unclear under this concept, but existing rating curves suggest that about 30,000 cfs could be released at elevation 3500 feet, About 900 megawatts of capacity are available at this level, a reduction of about one-third from the current maximum capacity due to the lower head, While powerplant bypasses would be eliminated, energy production would also be reduced, b - Routings of several magnitudes of inflow were performed to evaluate the amount of unintended storage that would temporarily accumulate in Lake Powell due to the routing effect, With the uncertainties of release capacity, the combined powerplantloutlet works capacity was assumed to be about 45,000 cfs, An examination of historic Lake Powell inflows showed that 45,000 cfs was exceeded about 70 percent of the time, This means that Lake Powell would gain storage in the spring this frequency of years in the future, c - Routings of average (1996), upper quartile (1993), and extreme (1983) years were made to determine the duration of inundation at various levels upstream of the dam, Starting conditions were assumed as an elevation of3500 feet and an ability to pass inflow up to the 45,000 cfs level. The following table shows the routing results: Year Type Max Inflow # Days of Max Elev (cfs) Elev> 3500 feet (feet) 3