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. Although the goal would be to maintain steady, or uniform, water releases downstream for selected durations, the ability to maintain a steady flow from one month to the next would depend on the accuracy of streamflow forecasts and the space available in Lake Powell. With the steady flow operations, estimated annual releases would be based on successive monthly forecasts. Monthly releases would be adjusted for forecast changes. One example is depicted in figure 4. The maximum change in releases to adjust for forecast changes between months would be 2,000 ds per day. Powerplant capacity would be exceeded only during periods of release through the outlet works to avoid spills or with the spillway if spills are unavoidable due to high water years. Power generation would be determined primarily by the steady water releases. All three of the steady flow alternatives could include pumping of river bottom sand on a one-time basis, similar to that previously described for the Mimic Pre-dam alternatives. For the steady flow alternatives, it is believed that the tributary nm-off downstream from Glen Canyon Dam would supply sediments from existing natural sources to the river channel pools and beaches would be less susceptible to erosion than with fluctuating flows; therefore sediment augmentation would not be included. However, some enhancement of selected beaches by sand pumping may have merit. Steady flow regimes are believed to permit differential warming of backwaters. Although GeES studies are still investigating backwater temperatures and other 10 Steady Flow - Year Round (AdjUll8cl Monthly lor Forecast Changes) f ! ...-- . . . I i . . . . . . . . . . : -......, .i.' l-.__. -------\_- .......... l__ '!.....- '----, ..--i--_____ -- ......-.... . __.... ..._......_.z 80 50 f2 0 ~ 40 ~ 8l ~ 30 -' w II: ~ 20 II: ::> 0 :I: 10 0 ...... 17.9 mal w/spills (1983) - - 13.6 mal (1987) - 6.2 mal (1989) Figure 4 - Example showing the effect of monthly forecast adjustments targeted steady flows for three representative water years aspects of river warming, it appears that multi-level intake structures for temperature control ma)!: not be needed for steady flow releases. The Year-Round Stead.J! Flow alternative would provide uniform releases throughout each year (subject to forecast adjustments between months), thus eliminating seasonal and daily river fluctuations to the extent possible. Targeted releases would be 11,400, 16,600, and 22,100 cis for annual volumes of 8.23, 12.0, and 16.0 million acre-feet, (maf) respectively. Maximum flow rates would be determined by the annual volume of water to be released, and could require use of the outlet works and spillway during high water years when Lake Powell is full. Minimum flows would be about 11,400 ds, unless lowered due to forecast adjustments. The Seasonally-Ad,iusted Steadg fllml alternative would provide steady releases within each of the four seasons keyed to ecosystem activities, such as fish spawning, downstream of the dam. Flows would remain steady within each month of a season, but would be subject to change at the beginning of each month to respond to forecast changes. Typical releases for an annual volume of 8.23 million acre feet would be; Oct - Dec 8,000 cis, Jan - Mar 11,000 ds, Apr - Jun 18,000 cis, Jul - Sep 8,000 ds. For an annual volume of 12 million acre feet the typical releases would be Oct - Dee 13,000 ds, Jan - Mar 16,000 ds, Apr - Jun 23,000 ds, Jul- Sep 13,000 cis.