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Description of Alternatives Hourly Operations 2. On the first of each month from January to June, a protection factor is added to the forecasted inflow so that more water is assumed to be coming into the reservoir than indicated by the forecast. 3. Throughout the streamflow forecast season (January 1 to July 1), operations are planned as though Lake Powell has 500,000 acre-feet less capacity than it actually has. This provides a storage buffer to further protect against unforecasted inflow. Hourly releases are set to reach monthly release volumes, to maintain established minimum flow rates, and to follow energy demand. Emergency conditions--such as search and rescue operations, generating equipment failures, or power system emergencies-may cause extreme departures from normal operations. Except for search and rescue operations, these departures are short lived (generally 1 hour or less) and their effects on water releases can be adjusted in a short time (less than 4 hours). Hourly power operations are most flexible during months with moderate release volumes. The need to maintain minimum flows in months with low release volumes limits flexibility to accommodate changing hourly power demands. If the reservoir is nearly full and inflow is extremely high, monthly releases are scheduled at or near maximum capacity most of the time, leaving little flexibility for hourly releases to change in response to power demand. Releases fluctuate when the generating units are being operated to follow changes in power system load, to produce peaking power, to regulate the power system, or to respond to power system emergencies. During a minimum release year, the greater the daily release volume the greater the daily fluctuation. To the extent possible within higher priority operating constraints, the following guidelines are used in producing hydroelectric power: • Maximize water releases during the peak energy demand periods, generally Monday through Saturday between 7 a.m. and 11 p.m. • Maximize water releases during peak energy demand months and minimize during low demand months • Minimize and, to the extent possible, eliminate powerplant bypasses Minimum Flow. Minimum flows are restricted to no less than 1,000 cfs from Labor Day until Easter and 3,000 cfs from Easter until Labor Day (the recreation season). Also during the recreation season, weekday releases must average no less than 8,000 cfs from 8 a.m. to midnight. The minimum flow for any given hour typically depends on the monthly release volume and the magnitude and predictability of electrical load Glen Canyon Dam EIS Summary 19