Glen Canyon Dam / Lake Powell - Snowpack conditions in the Upper Colorado River Basin have continued at or near average through the month of February and have entered March at 104% of average. One year ago, on March 1, 2008, the snowpack measured 126% of average so water year 2009 is shaping up to be somewhat drier than water year 2008. By this time of year the snowpack development season is about 80% complete and by the first week of April the snowpack typically peaks for the season.
The Colorado Basin River Forecast Center‘s March water supply forecast for Lake Powell for the April to July runoff season decreased from 8.0 million acre-feet (101% of average) to 7.8 million acre-feet (98% of average). Based on this forecast, with the projected operations of the upstream reservoirs and an 8.23 million acre-foot release from Lake Powell, the March 24-month study would project the end of water year elevation of Lake Powell to be 3642.48 feet above sea level. This projected elevation is 3.48 feet above the Equalization Level for 2009 (3639 feet above sea level). For this reason, the March 24-month study is projecting that a shift in operations from Upper Elevation Balancing to Equalization will likely occur in April 2009 (see Interim Guidelines Section 6.B.3) and the projected water year 2009 release volume from Lake Powell is 9.394 million acre-feet.
For April, if the forecasted April to July unregulated inflow to Lake Powell decreases by a significant volume (on the order of about 400,000 acre-feet), it is possible that the April shift to Equalization would not occur which would result in a projected water year 2009 release volume from Lake Powell of 8.23 million acre-feet.
The monthly release volume for March 2009 is scheduled to be 625,000 acre-feet. Daily average releases during March will be about 10,300 cfs. Monday through Friday releases will peak each afternoon to about 13,000 cfs with early morning releases of approximately 7,000 cfs. Weekend afternoon peak releases will be about 12,750 cfs with morning low releases near 7,000 cfs. The currently scheduled release volume for April 2009 is 750,000 acre-feet which will result in an average daily release of 12,600 cfs. Afternoon peaks will likely be about 15,300 cfs and early morning releases will likely be about 9,300 cfs.
Upper Colorado River Basin Hydrology
The overall precipitation rates during October and November 2008 were well below average at approximately 55% and 80% respectively. In December, however, conditions improved significantly with precipitation measuring approximately 185% of average. Unfortunately this wetter trend did not continue with precipitation in January and February measuring below average at 95% and 80% of average respectively. The overall water year precipitation rate through March 5, 2009 is right on average at 100% of average.
The Climate Prediction Center outlook for temperature and precipitation over the next 3 months indicates that temperatures in the southwest have an increased probability of being above average while precipitation has an increased probability of being below average in the Upper Colorado River Basin.
Upper Colorado River Basin Drought
The Upper Colorado River Basin is experiencing a protracted multi-year drought. Since 1999, inflow to Lake Powell has been below average in every year except water year 2005 and 2008.
In the summer of 1999, Lake Powell was essentially full with reservoir storage at 23.5 million acre-feet, or 97 percent of capacity. During the next 5 years (2000 through 2004) unregulated inflow to Lake Powell was well below average. This resulted in Lake Powell storage decreasing during this period to 8.0 million acre-feet (33 percent of capacity) which occurred on April 8, 2005. During 2005 and 2008 drought conditions eased somewhat with net gains in storage to Lake Powell. On September 30, 2008 the storage in Lake Powell was 14.5 million acre-feet (60 percent of capacity) which is still well below desired levels. Reservoir storage in the Colorado River Basin continues to be below desired levels with the overall Colorado River system storage as of March 1, 2009 of 32.7 million acre-feet which is 55.0 percent of capacity.
Updated: March 13, 2009
Rick Clayton
Email comments/inquires to: ResourceMgr@uc.usbr.gov