Salt Lake City, Utah
Released On: February 02, 2004
Reclamation, the U.S. Geological Survey, and the National Park Service have jointly released a supplemental Environmental Assessment and a Finding of No Significant Impact to the change in releases. The decision followed a review of the National Environmental Policy Act study that was completed in 2002 that provided for the test.
The experimental flows are designed to benefit humpback chub, a fish species native to the Grand Canyon. The experiment will evaluate whether non-native fish such as trout are negatively impacting the endangered humpback chubs by competing for key habitat space and by preying upon the chubs 75 miles downstream near the confluence with the Little Colorado River. Additionally, the flows are anticipated to benefit the trout upstream in the 16-mile stretch from the dam to Lee Ferry by reducing the trout population, thus increasing the viability and size of the fish. That stretch is within the Glen Canyon National Recreation Area and is managed for the sport fishery. The downstream river through Grand Canyon National Park is managed to benefit native fish species. The fluctuating releases complement an ongoing effort to mechanically remove non-native fish near the confluence.
Releases range between a daily high of 20,000 cubic-feet-per-second (cfs) to a low of 5,000 cfs. Currently the daily increasing flows have been starting at 9:00 in the morning. Beginning on February 4th, the flows will begin increasing at 7:00 AM, which is within the morning period of peak power demand. Also, on Sundays when the power demand is less, the releases will be reduced to a peak of 8,000 cfs instead of 20,000 cfs. This will conserve water for the weekday releases. The entire experiment is taking place within the predetermined monthly and annual release volume of water from Lake Powell and is not an additional impact to the reservoir during the ongoing drought.
Researchers have discovered that since 1991, when such significant fluctuations were ended, the trout population dramatically grew at the probable expense of the native humpback chub population. Scientists are trying to determine if the fluctuating flows can keep the trout population in check by impacting their spawning and other aspects of their lifecycle.
DOI | Recreation.gov | USA.gov
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