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Sun, Sept. 27

Lake Powell inflow below average but better than previously forecast

Though inflow to Lake Powell was only 42 percent of average in June, it was more than 200,000 acre-feet above the level forecast. Unregulated inflow last month was 1,100,000 acre-feet.

From April through July, unregulated inflow to the lake is expected to be about 4.2 million acre-feet, 53 percent of average. Water year inflow to Lake Powell (October-September) is projected to be 70 percent of average, boosted by heavy storm events in October that raised the lake by six feet.

Lake Powell reached a seasonal peak elevation of 3,611.7 feet on June 25. As of the first week of July, the elevation of Lake Powell was 3,611.2 feet with 12.85 million acre-feet of storage (53 percent of capacity).

The water surface elevation of Lake Powell will likely decrease between now and March. The projected elevation of Lake Powell by January is 3,599 feet.

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 73 percent of average. 

Water year 2007 will be another year of below average inflow.  The current projection for April through July runoff into Lake Powell is only 53 percent of average. Projected inflow to Lake Powell for the entire 2007 water year is 70 percent of average. With 2007 projected to be a below average inflow year, one sees that over the past 8 years (2000 through 2007, inclusive) inflow to Lake Powell will have been below average in all but one year (2005). 

Reservoir storage in Lake Powell and Lake Mead has decreased during the past 8 years. Reservoir storage in Lake Powell and Lake Mead is currently 53 and 49 percent of capacity, respectively.

Releases from Glen Canyon Dam in July 2007 will average 13,100 cubic feet per second (cfs) with a total of 804,000 acre-feet scheduled to be released for the month. Releases from Glen Canyon Dam in August 2007 will be similar to July. A total of 804,000 acre-feet is scheduled to be released August 2007, which is an average flow of 13,100 cfs. Releases are scheduled to be decreased in September.  The current schedule shows 603,000 acre-feet of release in September 2007.

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