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- 'c- ~ ~-- '-'~~,'7-' : NO ACTION ALTERNATIVE operations The operation of Glen Canyon Dam allows for a maximum water release of 31,500 cfs and a minimum of 1,000 cfs from Labor Day to Easter, and 3,000 cfs from Easter to Labor Day. Except during periods of very high runoff, the amount of water released from Glen Canyon Dam is varied on an hourly basis, often with two peaks daily. Power loads are greatest during the coldest winter and hottest summer months and therefore higher releases are scheduled during those months whenever possible. Maintenance work is scheduled in off release months during low volume periods when maintenance can be conducted without impacting the normal release patterns. The filling schedule flexibility in combination with the target of allowing one half million acre feet of vacant space allows the probability of spilling no more than one year in twenty. Fluctuations are a function of power generation and these fluctuations can cause the river level to change by up to 13 feet. The extent of fluctuation is in part a function of yearly run off and monthly volumes, but is more a result of load-following throughout each day. In a low water year (8.23 maf) hourly operational flexibility is reduced and the ability to fluctuate is limited by water availability. In a high water year (20 maf) there is also little operational flexibility due to large release volumes and there is little opportunity to manage the flows on an hourly basis. The greatest flexibility is in moderate runoff years when flows can fluctuate as much as 20,000 cfs in a 24 hour period. The average "extreme" ascending hourly ramp rate is around 9,200 cfs with a descending rate of -10700 cfs. Water released from the dam is drawn from approximately 250 feet below the top of the dam and is around 48 degrees F and is clear, containing very little sediment. No actions are proposed to change the water quality. The area between Lees Ferry and the dam is managed by the Arizona Department of Game and Fish as a "blue ribbon trout fishery" and averages 15,000 angler days annually. The National Park Service manages the area between the dam and Lees Ferry as a National Recreation Area. The area below Lees Ferry is managed by the National Park Service in accordance with the Grand Canyon River Management Plan. This Plan sets the limit at 115,500 white-water user-days for commercial 6