Laserfiche WebLink
<br />10 Chapter 2.0 Description of Alternatives <br /> <br />~-" ,W"l .. <br />..\i " :,\ <br />'" <br /> <br />Operating criteria adopted in 1997 were designed to protect or enhance downstream <br />resources while allowing limited flexibility for power operations. Criteria such as <br />minimum flows, maximum flows, ramp rates, and allowable daily fluctuations were <br />modified in the FEIS and ROD. <br /> <br />Annual and monthly releases implement the long-range operating criteria objectives <br />of 8.23-million acre-feet (maf) minimum annual releases, storage equalization between <br />Lake Powell and Lake Mead, and avoidance of anticipated spills. Annual and monthly <br />release volumes are projected for different hydrologic conditions prior to the beginning <br />of the water year (October-September) and are generally described in an annual <br />operating plan. Estimated monthly release volumes under the No Action Alternative for <br />the period September 2002-September 2004 are listed in table 2.2, while daily release <br />patterns for this period are depicted in figure 2.1. Most probable annual release volumes <br />as of September 2002 are 8.23 maf for the 2003 water year and 9.6 maf for the 2004 water <br />year. <br /> <br />Scheduled monthly release volumes are updated at least monthly during the water <br />year (October-September). The actual minimum and maximum releases from the dam <br />for a given day depend on the monthly release volume, the allowable daily fluctuation, <br />and the demand for hydroelectric power. The actual releases are usually higher than the <br />minimum and lower than the maximum allowed under the ROD. The allowable daily <br />fluctuation of 5,000, 6,000, or 8,000 cfs/24 hours depends on the monthly release volume <br />and is designed to constrain the daily change in river stage. <br /> <br />The downramp rate in the ROD was conservatively set to reduce seepage-based <br />erosion of sandbars in Glen and Grand canyons and to avoid stranding of fish. The <br />upramp rate was set to further reduce operation-related impacts to canyon resources, <br />although the processes linking ramp rates with resource effects are still under <br />investigation. <br /> <br />Habitat maintenance flows are dam releases at powerplant capacity (about 31,000 cfs <br />at full reservoir elevation) and were anticipated to occur in most years (Reclamation <br />1995a). Beach/habitat-building flows under the ROD exceed powerplant capacity and <br />were expected to occur infrequently when high reservoir elevations create dam safety <br />concerns. The two types of releases, which had similar purposes of reforming <br />backwaters and maintaining sandbars, were not to be scheduled in the same year and <br />neither was to occur in a year when there was concern for the effects on sensitive <br />resources, such as sediment or endangered species. <br />