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Enclosure 1 DESCRIPTION OF PREFERRED ALTERNATIVE FOR THE OPERATION OF GLEN CANYON DAM low Volume Months Medium Volume High Volume Months Months Minimum Release 8,000 between (cfs) 7am and 7pm same same 5,000 at niqht Habitat Maint. Between 30,000 same same Flow {cfs\ and 33,200 Maximum Release 25,000 same same (cfs) (will be exceeded for habitat maint. ) Daily Fluctuation 5,000 6,000 8,000 (cfs\24 hrs I. Monthly Release <600,000 600,000 to >800,000 Volume (acre- 800,000 feet) Ramp rate 4,000 up same same (cfs\hr) I,500 down The above table displays the parameters of the Preferred Alternative. Habitat Maintenance Flows, designed to re-form backwaters and maintain sandbars, will consist of high, steady releases within powerplant capacity of 33,200 cfs for 1 or 2 weeks in March, or other months if recommended through the Adaptive Management Program. These flows have been selected to redistribute sediment accumulation at low elevations, including in backwaters; rebuild portions of sandbars above the normal peak stage; and prevent return channels from becoming dominated with vegetation. Although habitat maintenance flows are defined as steady, minor fluctuations of up to plus or minus I,OOO cfs would be permitted to regulate voltage within the power grid. The month of March was selected to allow backwater channels to re-form prior to the humpback chub spawning period and because more sediment is likely to be .) suppl ied by tributary flow in March than later in the spring. i .-"ff. l1 LiVe..,7to d' Habitat maintenance flows would not be scheduled when the projecto~rage in Lake Powell on January 1 is greater than 19 million acre feet.~u;iv~elease volumes under such conditions are typically greater than the minimum annual release volume of 8.23 maf, and such flows already may be near or exceed powerplant capacity. Maintenance flows would begin by increasing flows at a rate no greater than 4,000 cfs per hour and would conclude by decreasing flows back to the normal operating range at a rate no greater than 1,500 cfs per hour. The limit on daily change in flow would not apply during these transitions.