Glen Canyon Dam Update

Glen Canyon Dam Operations

Releases from Glen Canyon Dam in November 2006 will average 10,000 cubic feet per second (cfs) with a total of 600,000 acre-feet scheduled to be released for the month. On Mondays through Fridays in November, daily release fluctuations due to load following will likely vary between a low of 7,000 cfs (during late evening and early morning off-peak hours) to a high of 13,000 cfs (during daylight and early evening on-peak hours). On Saturdays, release fluctuations will likely vary between a low of 7,000 cfs to a high of 12,500 cfs. On Sundays, release fluctuations will likely vary between a low of 7,000 cfs to a high of 12,000 cfs.

In December 2006, releases will be increased from the November level. A total of 800,000 acre-feet (an average of 13,000 cfs) are scheduled to be released in December 2006

Upper Colorado River Basin Hydrology

The "Four Corners" region experienced extraordinary amounts of precipitation during October 2006. Precipitation events were particularly intense in the vicinity of Lake Powell. Record-breaking daily flows for the month of October were observed on the San Juan, Dolores, San Rafael, Fremont/Dirty Devil, Escalante, and Paria Rivers in the first half of October. The most exceptional of these high flows were the flood flows on the Fremont/Dirty Devil on October 6 and 7, 2006. The stage (level of the river) of the Dirty Devil (at the "Dirty Devil above Poison Springs Wash near Hanksville, Utah" surface water discharge station) increased by more than 15 feet during the flood event.

The flow of the Dirty Devil River during the event is currently undetermined as the stage reached such levels at which flows are not known. Hydrologists from the United States Geological Survey are in the process of performing analysis to estimate the peak flow and total volume from this flood flow event. Also, it should be noted, a second high flow event occurred on the Dirty Devil River on October 17-18, 2006.

Localized inflow from the Dirty Devil River and other drainages (which outlet into Lake Powell) resulted in remarkable increases in Lake Powell on October 6, October 7, and October 8, 2006. Daily increases in the water surface elevation of Lake Powell on these three days were 1.33 feet, 0.97 feet, and 0.74 feet, respectively. Such daily increases in Lake Powell are unprecedented in the month of October. Every drainage and arroyo which outlet into Lake Powell was flowing during this period. Literally hundreds of waterfalls were observed in the sandstone cliffs which perimeter Lake Powell during and after these storm events.

Numerous other precipitation events, not only in the Four Corners region but throughout the Upper Colorado River Basin, in October, resulted in much above average inflow. Unregulated inflow in October 2006 was 1,018,000 acre-feet or 184 percent of average. This volume does not include unmeasured localized inflow, however, which could be as high as 350,000 acre-feet of additional water.

Lake Powell rarely increases in storage during the month of October. However, in October 2006, Lake Powell increased in storage by 609,000 acre-feet, gaining 6.2 feet in elevation. The current elevation of Lake Powell (November 1, 2006) is 3,608.0 feet. Reservoir storage is currently 12.53 million acre-feet, 52 percent of capacity.

Inflow to Lake Powell has decreased from the very high levels seen in early and mid-October. Inflow is currently about 11,000 cfs, with the level of Lake Powell holding nearly steady. Inflow is expected to decrease during November 2006, and the water surface elevation of Lake Powell will likely decrease during the month as well. Decreases in the water surface elevation of Lake Powell are projected to continue through the winter until April 2007, when anticipated snowmelt runoff will cause the water surface level to increase once more. The projected elevation of Lake Powell on January 1, 2007 is now about 3,605 feet.

Upper Colorado River Basin Drought

The Upper Colorado River Basin experienced five consecutive years of extreme drought from September 1999 through September 2004. In the summer of 1999, Lake Powell was essentially full with reservoir storage at 97 percent of capacity. Inflow volumes for five consecutive water years were significantly below average. Total unregulated inflow in water years 2000, 2001, 2002, 2003, and 2004 was 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.

Hydrologic conditions improved in water year 2005 in the Upper Colorado River Basin. Lake Powell increased by 2.77 million acre-feet (31 feet in elevation) during water year 2005. Unregulated inflow to Lake Powell in water year 2005 was 105 percent of average.

Unfortunately, in 2006, there was a return to drier condition in the Colorado River Basin. Unregulated inflow to Lake Powell in water year 2006 was 73 percent of average. Over the past 7 years (2000 through 2006, inclusive) inflow to Lake Powell has been below average in all but one year (2005).

Water year 2007 (which began on October 1, 2006) is off to a good start. Precipitation in the Colorado River Basin in October 2006 was much above average, and Lake Powell increased by 6.2 feet during the month, in large part due to exceptional precipitation events in the regions surrounding the lake. Nevertheless, historical records show that it is common to have periods of above average precipitation and runoff during a protracted multi-year drought. The drought in the Colorado River Basin may not be over.

This release courtesy Tom Ryan, United States Bureau of Reclamation.