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<br />2004 OPERATIONS SUMMARY AND RESERVOIR STATUS <br /> <br />Once again, drier than average hydrologic conditions were observed in the Colorado Rjver Basin in <br />2004, marking the fifth consecutive year of drought in the basin. Basinwide precipitation was <br />89 percent of average during water year 2004 with snowpack accumulations also being below normal <br />levels. Total unregulated(2) inflow into Lake Powell for water year 2004 was 6.13 million acre-feet <br />(maf) or 7,560 million cubic meters (mcm), only 51 percent of average. <br /> <br />Hydrologic conditions in the Colorado River Basin appeared to be more favorable in the winter of <br />2003~2004 than in the previous 4 years. During the winter period, basinwide snowpack was near <br />average and at times above average. On March 1,2004, basinwide snowpack in the Upper Colorado <br />River Basin was 97 percent of average, with the forecasted April through July inflow to Lake Powell <br />at 82 percent of average. However, March 2004 was an exceptionally warm and dry month <br />throughout the basin. A significant deterioration of the snowpack occurred during the month. By <br />April 1 ,2004, basinwide snowpack had decreased to 66 percent of average, a reduction of <br />31 percentage points in only 1 month. At that time, inflow projections to Lake Powell were reduced <br />to 50 percent of average. Further reductions ofthe inflow forecast occurred in May and June as the <br />Upper Colorado River Basin experienced dry spring conditions for yet another year. Unregulated <br />inflow into Lake Powell during the April through July runoff period in 2004 was 3.64 maf (4,490 <br />mcm), or 46 percent of the 30 year average(3). The volume of runoff in the basin in 2004 was <br />reduced due to very dry antecedent soil moisture conditions resulting from four previous years of <br />drought. <br /> <br />Water year 2004 marked the fifth consecutive year with below average inflow into Colorado River <br />reservoirs. Unregulated inflow to Lake Powell was 62, 59, 25, and 51 percent of average in water <br />years 2000, 2001,2002, and 2003 respectively. Reservoir storage at Lake Powell and Lake Mead <br />declined for the fifth straight year. During water year 2004, Lake Mead storage decreased by 1.681 <br />maf (2,074 m cm), and Lake Powell storage decreased by 2 .941 m af (3,628 mc:m). Storage in <br />reservoirs upstream of Lake Powell increased by approximately 0.395 maf (487 mcm) in water year <br />2004. At the beginning of water year 2004, Colorado River total system storage was 57 percent of <br />capacity. As of September 30,2004, total system storage was 50 percent of capacity, a decrease of <br />approximately 4.238 maf(5,228 mcm). <br /> <br />Tables l(a) and 1 (b) list the October 1, 2004, reservoir vacant space, live storage, water elevation, <br />percent of capacity, change in storage, and change in water elevation during water year 2004. <br /> <br />(2) Unregulated inflow adjusts for the effects of operations at upstream reservoirs. It is computed by adding the <br />change in storage, and the evaporation losses from upstream reservoirs to the observed inflow. UnregulElted inflow is <br />used because it provides an inflow time series that is not biased by upstream reservoir operations. <br />(3) Inflow statistics throughout this document will be compared to the: 30-year average, 1971-2000. <br /> <br />4 <br />