2004 Dam Operations;
Some Questions and Answers

excerpts are from: Glen Canyon Dam - Lake Powell Operations & Experimental Flows, Bureau of Reclamation monthly update, Feb. 4, 2004, Tom Ryan
Experimental Flows
—Daily high fluctuating releases from Glen Canyon Dam, as part of the Glen Canyon Dam experimental flows, are being implemented from January through March 2004… between a high of 20,000 cubic feet per second (cfs) to a low of 5,000 cfs.
—Beginning February 4, 2004 the high fluctuating release pattern is being adjusted [2 more hours/day of the 20k cfs high release Mondays-Saturdays, and only 8k cfs release on Sundays].
—Scientists have recognized that the humpback chub population has been in general decline since highly fluctuating flows were curtailed in November of 1991. Those flows helped keep the non-native fish, especially the rainbow and brown trout, in check.
—The Finding of No Significant Impact on the experimental flows can be found at http://www.uc.usbr.gov/amp/flow_ fonsi.pdf.
Why is the Bureau of Reclamation releasing experimental flows from the dam?
Scientists determined that Record of Decision flows from the dam were failing to conserve sediment and endangered native fish in Grand Canyon. So, they designed dam release experiments that may stem the loss of those critical resources. They are also conducting mechanical removal of non-native fish from the river near the mouth of the lcr and in the mouth of Bright Angel Creek to reduce competitive pressures on the chub.
Why the high daily fluctuations from January through March?
These are called trout suppression flows. This is the second year of a two year test to see if large daily fluctuations can ‘knock back’ the yearly trout spawn, assuming the trout are responsible for eating and competing with the endangered humpback chub. It’s also hypothesized that this will improve the Lees Ferry trout fishery by fostering the growth of larger trout.
Why are the trout suppression flows being changed midway through the experiment?
Western Area Power Administration miscalculated the hydropower costs. They originally thought this would be an economic boon, but found they had to buy energy on the ‘spot market’ for the first two hours of each day at exorbitant rates to satisfy their long-term peaking power contracts. This caused a reduction in revenue from the dam’s generators.
How do we know that high daily fluctuations in dam releases helped keep the trout in check?
We don’t understand the cause(s) of chub decline. Cause-effect relationships are complex and probably multiple. Other possible causes include: changes in the Little Colorado River flows due to changes in watershed management, climatic variation, increased handling of native fish by scientists, and changes to the aquatic food base.

Dam Releases for 2004
Monthly release volumes in February, and March 2004 are scheduled to be 744,000 and 807,000 acre-feet, respectively, which averages out to about 13,000 cfs per day. In April, high fluctuating releases will end. Releases in April, 2004 will likely be 600,000 acre-feet which averages out to about 10,000 cfs.
What will dam releases be during the river running season April-October, 2004?
Dam releases will likely be similar to last year. A minimum of 8.23 million acre feet of water must pass through the dam annually and it is apportioned as 12 monthly volumes. Larger daily fluctuations occur with higher monthly volumes, smaller daily fluctuations with lower monthly volumes. An average daily flow of 10,000 cfs means that daily fluctuations will range from about 7,500 to 12,500 cfs each day (April-May). Average daily flows will likely increase to 13,000 cfs (June-August) then decrease to 8,000 cfs (Sept.-Dec.).
Current Basin Conditions
—As of February 4, 2004, snowpack in the Colorado River Basin is 96 percent of average. Because of the extended drought, the snowpack lies atop a mantle of very dry soil. This scenario is not favorable for this spring’s runoff, as much of the melting snow will be absorbed by the soil. The National Weather Service’s February inflow forecast is calling for 6.5 million acre-feet of unregulated inflow to Lake Powell in April through July. This is only 82 percent of average.
—The Colorado River Basin is now in its 5th year of drought. Inflow volumes have been below average for 4 consecutive years. Unregulated inflow in water year 2003 was only 53 percent of average. Unregulated inflow in 2000, 2001 and 2002 was 62, 59, and 25 percent of average, respectively. Inflow in 2002 was the lowest ever observed since the completion of Glen Canyon Dam in 1963.
—Low inflows have reduced water storage in Lake Powell. On December 5, 2003, the elevation of Lake Powell dropped below 3600 feet. The last time the water surface elevation was this low was in 1973. The current elevation (as of February 3, 2004) of Lake Powell is 3,591 feet (109 feet from full pool). Current storage is 11.0 million acre-feet (45 percent of capacity).
What is meant by the term ‘unregulated inflow to Lake Powell’?
This is the amount of water that would enter Lake Powell if there were no dams or diversions upstream. So, it’s approximate, not actual.
How much longer will this drought continue?
It’s anybody’s guess, but it’s shaping up to be worse than the 1930s dust bowl drought. Climatic studies of the Colorado Plateau suggest that it may continue, on and off, over the next couple of decades.

Andre Potochnik