Glen Canyon Dam and Lake Powell
Inflows to Lake Powell have increased significantly in the past several weeks as a result of runoff from the melting snowpack. From mid April to early May inflows have increased from about 7,000 cubic feet per second (cfs) to over 30,000 cfs. As a result, the reservoir elevation of Lake Powell has risen over 5 feet in the past 2 weeks. As of May 10, 2009 the reservoir elevation of Lake Powell was 3614.62 feet above sea level and the Castle Rock Cut-Off is now open.
The Colorado Basin River Forecast Center‘s May water supply forecast for Lake Powell for the April to July runoff season increased to 7.3 million acre-feet (92% of average). The May forecast increased by 100,000 acre-feet as compared to the April Forecast. Based on this forecast, with the projected operations of the upstream reservoirs and a scheduled 8.23 million acre-foot release from Lake Powell in water year 2009, the May 24-month study projects the end of water year elevation of Lake Powell to be 3638.71 feet above sea level.
The monthly release volume for May 2009 is scheduled to be 600,000 acre-feet. Daily average releases during most of May will be about 10,250 cfs. Monday through Friday releases will peak each afternoon to about 12,500 cfs with early morning releases of approximately 6,500 cfs. Weekend afternoon peak releases will also be about 12,500 cfs with morning low releases near 6,500 cfs. The release volume for June 2009 is 625,000 acre-feet which will result in an average daily release of 10,500 cfs. Afternoon peaks will likely be about 12,500 cfs and early morning releases will likely be about 6,500 cfs.
Beginning on May 21, 2009 at approximately 6:00 pm, releases from Glen Canyon Dam are scheduled to be steady at 8,000 cfs for a 5 day period so that the Grand Canyon Monitoring and Research Center (GCMRC) can conduct over-flight data gathering of the channel of the Colorado River thought Grand Canyon National Park. Releases are scheduled to continue to remain steady at 8,000 cfs until approximately 4:00 am on May 27, 2009. However, if GCMRC is able complete the planned over flight work before this date and time, operations at Glen Canyon Dam would resume normal daily fluctuations.
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 conditions returned to a wetter pattern with precipitation measured at 125% of average. The overall water year precipitation rate through May 10, 2009 is 102% 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 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 May 1, 2009 the storage in Lake Powell was 12.9 million acre-feet (53 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 May 1, 2009 of 32.0 million acre-feet which is 54 percent of capacity.
RRFW thanks Rick Clayton of the USBOR for his assistance in providing information for this notification.
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