Join Date: Dec 2004
RRFW Riverwire Glen Canyon Dam Update
RRFW Riverwire Glen Canyon Dam Update
June 16, 2008
Glen Canyon Dam Operations
The monthly release volume in June 2008 is scheduled to be 790,000 kaf. Weekday releases will average about 13,500 cfs with afternoon peaks to about 15,750 cfs and off peak lows to about 9,750 cfs. Saturday and Sunday releases will average about 12,900 cfs with afternoon peaks to about 15,500 cfs and off peak lows to about 9,750 cfs.
Inflows to Lake Powell in early June increased to over 75,000 cfs with the elevation of Lake Powell increasing at nearly 1 foot per day. The current elevation of Lake Powell (June 9, 2008 is 3,619.18 feet above sea level. The Castle Rock Cut will likely be passable by mid June and the elevation of Lake Powell will likely peak near 3,638 feet by early August.
Releases from Glen Canyon Dam for the remainder of water year 2008 will be governed by the Equalization Tier of the Interim Guidelines for the Operation of Lake Powell and Lake Mead (Interim Guidelines). Under the Equalization Tier, the water year annual release volume can be above 8.23 million acre-feet (maf). For the June 2008 24-Month Study, the controlling Equalization objective for water year 2008 is an end of water year Lake Mead elevation of 1,105 feet above sea level. To achieve this objective, the water year annual release volume from Glen Canyon Dam will be controlled as practicably as possible to achieve an end of water year elevation at Lake Mead of 1105. The June 2008 24-month study projects the annual release volume from Glen Canyon Dam that would accomplish this objective to be 8.955 maf which equates to an equalization volume (volume in excess of 8.23 maf) projected to be 725 kaf. These projected values, as well as the monthly release volumes, for the remaining months of water year 2008 will be adjusted as conditions change.
Upper Colorado River Basin Hydrology
Precipitation in the basin above Lake Powell was above normal in May (105% of average). The precipitation above Lake Powell in March and April was below normal at 60% of normal over the 2 month period. The overall precipitation in the Upper Colorado River Basin for water year 2008 so far is 107% of normal. Temperature conditions in May were below normal which has preserved the snowpack somewhat.
The unregulated inflow to Lake Powell in May was 2,644,000 acre-feet (115% of normal). This was 556,000 acre-feet below the level forecasted in May and is largely attributed to the below normal temperatures experienced in the basin during May. Forecasted levels for June and July in the current (June) forecast have been increased to reflect the shortfall in May with the overall April through July volume forecasted to remain unchanged from May at 9.2 maf (116% of average).
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 one.
In the summer of 1999, Lake Powell was essentially full with reservoir storage at 23.5 million acre-feet, or 97 percent of capacity. Inflow to Lake Powell in 1999 was 109 percent of average. The manifestation of drought conditions in the Upper Colorado River Basin began in the fall months of 1999. A five year period of extreme drought occurred in water years 2000, 2001, 2002, 2003, and 2004 with unregulated inflow to Lake Powell only 62, 59, 25, 51, and 49 percent of average, respectively. Lake Powell storage decreased through this five-year period, with reservoir storage reaching a low of 8.0 million acre-feet (33 percent of capacity) on April 8, 2005.
Drought conditions eased in water year 2005 in the Upper Colorado River Basin. Precipitation was above average in 2005 and unregulated inflow to Lake Powell was 105 percent of average. Lake Powell increased by 2.77 million acre-feet (31 feet in elevation) during water year 2005. But as is often the case, one favorable year does not necessarily end a protracted drought. In 2006, there was a return to drier conditions in the Colorado River Basin. Unregulated inflow to Lake Powell in water year 2006 was only 71 percent of average.
Water year 2007 was another year of below average inflow with unregulated inflow into Lake Powell at 68 percent of average. Over the past 8 years (2000 through 2007, inclusive), inflow to Lake Powell has been below average in all but one year (2005). Drought conditions have eased again in water year 2008 with projected inflows to the main stem Colorado River reservoirs at or above normal. Reservoir storage in the Colorado River Basin, however, is still below desired levels with the overall Colorado River system storage (above Lake Mead) projected to be about 60% of capacity at the end of water year 2008.
Reservoir storage in Lake Powell and Lake Mead has decreased during the past 8 years but is projected to increase by the end of water year 2008. Current reservoir storage in Lake Powell is 53 percent of capacity. Storage in Lake Mead is 49 percent of capacity.
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