Bypass valves were to be opened at Glen Canyon Dam this morning, releasing a 41,000 cfs flow over two and a half days to redistribute sediment in the Colorado River.
Last Friday, the Bureau of Reclamation released a final environmental assessment and a Finding of No Significant Impact that authorized the test to begin this morning.
The FEA evaluated the impact of the proposed experimental flows on a wide range of environmental and socioeconomic resources.
Scientists and resource managers from Interior's U.S. Geological Survey (USGS), Reclamation, National Park Service, U.S. Fish and Wildlife Service, and Bureau of Indian Affairs are taking part in the experiement.
The 2008 high flow test will be similar to the previous high flow experiments conducted by the joint Interior agencies in 2004, but the amount of sediment available for the 2008 experiment is three times larger.
Based on the previous experiments, scientists have concluded that more sand is needed to rebuild sandbars throughout the 277-mile reach of Grand Canyon National Park than was available in 1996 or 2004.
Currently, sand supplies in the river are at a 10-year high with a volume about three times greater than in 2004 due to tributary inflows below the dam over the past 16 months.
During the high-flow experiment, Reclamation will release water through Glen Canyon Dam's powerplant and bypass tubes to a maximum amount of approximately 41,500 cubic feet per second (cfs) for about 60 hours.
Operational plans called for the experimental flows to begin increasing yesterday evening with power plant bypass flows to begin this morning.
From Feb. 8-22, Reclamation solicited public comments on the environmental assessment. The final environmental assessment and FONSI conclude that implementation of the preferred alternative - the March 2008 high-flow test and fall steady flow experiment from Glen Canyon Dam - would have no significant impacts on the quality of the human environment or the natural resources below the dam.
The FEA and FONSI are available for review at: www.usbr.gov/uc/envdocs/ea/gc/2008hfe/index.html