The 60-hour high-flow test, through both the bypass tubes and the powerhouse, was expected to redistribute sand from the river bottom, forming sandbars and beaches within the canyon. The experiment is part of a research effort by three agencies of the Interior Department: the Bureau of Reclamation, the U.S. Geological Survey, and the National Park Service.
Sandbars within the Grand Canyon provide habitat for wildlife, camping beaches, and sand to protect archaeological sites, Interior said. High flows also create areas of low-velocity flow, or backwaters, used by young fish, particularly the endangered humpback chub.
The 2008 test is different from similar releases in 1996 and 2004. Scientists concluded more sand, than was available in the prior years, is needed to rebuild sandbars through the 277-mile river reach. Sand supplies in the river are at a ten-year high with a volume three times greater than was available in 2004.
Since 1996, releases from Glen Canyon have ranged from 8,000 to 20,000 cfs. Monthly releases later in the year will be adjusted downward to account for water released during the experiment.
The agencies last year scoped the long-term experimental plan for operation of Glen Canyon Dam, on the Colorado near Page. (HNN 4/24/07) Experimental operations are to learn which elements of dam operations and other management actions would lead to recovery and long-term sustainability of downstream resources, while minimizing effects to hydropower capability and flexibility.