Glen Canyon Dam / Lake Powell
The inflow to Lake Powell reached its peak for WY2009 on May 28, 2009 when it reached 54,921 cfs (cubic feet per second). Since that time the inflow has decreased somewhat and is averaging over 44,000 cfs over the past 7 days as of June 9, 2009. The unregulated inflow during May was well above forecasted levels at 2.9 million acre-feet (maf) which was about 400,000 acre-feet above the May forecast. The elevation of Lake Powell is currently rising at about 6 inches per day. During the month of May 2009, the elevation of Lake Powell increased more than 18 feet to 3629.7 feet above sea level (70.3 feet from full pool) on June 1, 2009. The elevation of Lake Powell will likely increase another 10 to 12 feet during the month of June and is projected to peak by mid August at near 3642 feet above sea level. The snowpack this year has melted earlier than expected and is all but melted out at this point except in the very high elevation regions.
For June 2009, the scheduled release volume from Glen Canyon Dam is 625,000 acre-feet which is an average daily release of approximately 10,500 cfs. During weekdays, the peak release rate from Glen Canyon Dam during the afternoon will be approximately 13,000 cfs and the early morning lows will be about 7,000 cfs. During the weekends in June, the peak afternoon release rate will be approximately 12,750 cfs and the early morning lows will be about 7,000 cfs. The projected release volume in July will be approximately 830,000 acre-feet (average daily release of approximately 13,500 cfs) with an approximate afternoon peak release rate of about 17,500 cfs.
The Colorado Basin River Forecast Center’s June final water supply forecast for Lake Powell for the April to July runoff season remained unchanged at 7.1 million acre-feet (90% of average). While the unregulated inflow during May was 2,900,000 acre-feet which was over 400,000 acre-feet above forecasted levels, it is possible that the unregulated inflow during June and July will be less than expected due to the early runoff conditions that have occurred so far this year. The unregulated inflow to Lake Powell forecasted for June is 2.3 maf while for July the forecast is for 1.1 maf.
The operation of Lake Powell in this June 2009 24-Month Study is pursuant to the December 2007 Record of Decision on Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations of Lake Powell and Lake Mead (Interim Guidelines), and reflects the 2009 Annual Operating Plan (AOP). Pursuant to the Interim Guidelines, the Upper Elevation Balancing Tier is the operational tier for water year 2009 for Glen Canyon Dam.
The April 2009 24-Month Study projected the end of water year elevation at Lake Powell to be below the 2009 Equalization Elevation of 3639 feet and the projected end of water year elevation at Lake Mead to be above elevation 1075 feet. Pursuant to Sections 6.B.1. and 6.B.4. of the Interim Guidelines, the annual release volume will be 8.23 million acre-feet from Glen Canyon Dam during water year 2009 which is reflected in the June 24-Month Study.
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, February and March measuring 95%, 75% and 65% of average respectively. In April and May conditions returned to a wetter pattern with precipitation measured at 120% and 105% of average, respectively. The overall water year precipitation rate through June 9, 2009 is 101% of average.
The Climate Prediction Center outlook for temperature over the next 3 months indicates that temperatures in the southwest have an increased probability of being above average while precipitation also has an increased probability of being above average in the Upper Colorado River Basin.
Upper Colorado River Basin Drought
The Upper Colorado River Basin continues to experience a protracted multi-year drought. Since 1999, inflow to Lake Powell has been below average in every year except water years 2005 and 2008. In the summer of 1999, Lake Powell was close to 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. As of June 9, 2009 the storage in Lake Powell was 14.8 million acre-feet (63 percent of capacity) which is 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 June 1, 2009 of 34.5 million acre-feet which is 58 percent of capacity.
This report courtesy of Rick Clayton, US Bureau of Reclamation.
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