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Old 02-13-2009   #1
Tom Martin's Avatar
Flagstaff, Arizona
Join Date: Dec 2004
Posts: 818
RRFW Riverwire Glen Canyon Dam Update

RRFW Riverwire Glen Canyon Dam Update
February 13, 2009

Glen Canyon Dam Operations

Snowpack conditions in the Upper Colorado River Basin continue to be above average through the month of January. On January 1, 2009 the snowpack above Lake Powell measured only 107% of average. By January 31, 2008 this snowpack had improved to 111% of average. As of February 11, 2009 the snowpack measured 106% of average.

The Colorado Basin River Forecast Center‘s February water supply forecast for Lake Powell for the April to July runoff season is 8.0 million acre-feet (101% of average). Based on this forecast, Reclamation is currently projecting a shift in operations from Upper Elevation Balancing to Equalization in April 2009 (see Interim Guidelines Section 6.B.3). For this reason, the February 24-Month Study projects the annual release from Lake Powell during water year 2009 to be 9.431 million acre-feet. As forecast conditions change, Reclamation will update these projections monthly.

The monthly release volume for February 2009 is scheduled to be 600,000 acre-feet. Daily average releases during January will be about 10,000 cfs. Monday through Friday releases will peak each afternoon to about 13,500 cfs with early morning releases of approximately 7,500 cfs. Weekend afternoon peak releases will be about 13,250 cfs with morning low releases near 7,500 cfs. The currently scheduled release volume for March 2009 is 625,000 acre-feet which will result in an average daily release of 10,200 cfs. Afternoon peaks will likely be about 12,900 cfs and early morning releases will likely be about 6,900 cfs.

Upper Colorado River Basin Hydrology

Precipitation rates during October and November 2008 were well below average at 55% and 80% respectively. In December, however, conditions improved significantly with the estimated precipitation rate of about 185% of average. The preliminary precipitation total for January 2009 was 95% of average. The overall water year precipitation rate through February 12, 2009 is 104% 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 will likely be near 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 February 1, 2009 of 33.0 million acre-feet which is 55.5 percent of capacity.

This release was posted courtesy Rick Clayton, Hydraulic Engineer, Upper Colorado Region US Bureau of Reclamation.
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