Annual Operating Plan For Colorado River Reservoirs 2004

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January 7, 2004 5 2003 OPERATIONS SUMMARY AND RESERVOIR STATUS Drier than average hydrologic conditions were observed in the Colorado River basin in water year 2003, marking the fourth consecutive year of drought in the basin. Basinwide precipitation was 89 ' percent of average during water year 2003 with snowpack accumulations also being below normal levels. As the spring snowmelt season began on April 1, 2003, snowpack levels throughout the Colorado River Basin averaged about 80 percent of average. The volume of runoff in the basin was reduced, however, due to very dry antecedent soil moisture conditions resulting from three previous years of drought. Unregulated') inflow into Lake Powell during the April through July runoff period in 2003 was 3.92 maf (4,840 mcm) or 49 percent of the 30 year average(2). Total unregulated inflow ' into Lake Powell for water year 2003 was 6.36 maf (7,845 mcm) or 53 percent of average. ' Water year 2003 marked the fourth consecutive year with below average inflow into Colorado River reservoirs. Unregulated inflow to Lake Powell was 62, 59, and 25 percent of average in water years 2000, 2001, and 2002, respectively. Reservoir storage at Lake Powell and Lake Mead declined for ' the fourth straight year. By the end of water year 2003, Lake Mead storage decreased by 1.48 maf (1,830 mcm). Storage in Lake Powell decreased by 2.36 maf (2910 mcm). Storage in reservoirs upstream of Lake Powell increased by approximately 0.055 maf (68 mcm) in 2003. At the beginning ' of water year 2003, Colorado River total system storage was 64 percent of capacity. Total Colorado River system storage decreased by approximately 3.8 maf (4,690 mcm) during water year 2003. As of September 30, 2003, total system storage was 57 percent of capacity. Even though Colorado River reservoir storage has been reduced during 2003, deliveries of water to meet obligations pursiiarit to applicable provisions of "The Law ofthe River" were maintained. Preliminary Colorado River water delivery accounting data for calendar year (CY) 2002, compiled ' pursuant to Article V of the Decree, indicated that requests for water deliveries by agricultural users in California during CY 2002 had the potential to exceed the maximum amount of water available under the determinations made in the 2002 AOP approved and transmitted on January 14, 2002. In light of the potential for such overuse within the Lower Basin, and after consultation with members of the CRMWG, a supplement to the 2002 AOP was approved on November 22, 2002. The supplement to the 2002 AOP addressed this potential CY 2002 overuse and established appropriate Unregulated inflow adjusts for the effects of operations at upstream reservoirs. It is computed ' by adding the change in storage, and the evaporation losses from upstream reservoirs to the observed inflow. Unregulated inflow is used because it provides an inflow time series that is not biased by upstream reservoir operations. ' (2) Inflow statistics throughout this document will be as compared to 30 -year averages.