Experimental water releases from Glen Canyon Dam on the Colorado River above Grand Canyon were scheduled to begin today after receiving environmental clearance last month.
Intended to test methods for protecting the river’s ecosystem downstream of the dam, the project was the result of a recommendation from a federal advisory committee. The work group based its conclusions on studies that had been conducted by the U.S. Geological Survey.
Barry Wirth of the Bureau of Reclamation’s public affairs office said there are two aspects to the experiment.
"The first relates to sediment conservation in Grand Canyon," Wirth said in a news release. "Scientists propose using high flow tests to move sediment to rebuild beaches and sand bars."
That may sound familiar to people who followed the last experimental flood in the spring of 1996. Wirth said these flows will differ, because they will be timed to make use of sand and sediment that enters the Colorado River from tributary flows of the Paria River.
"Seasonal monsoon storms provide an average of 1 million tons of sediment a year to the Colorado River from the Paria River," Wirth said. "High flow tests would be timed to make use of this introduced sediment. In this sense, high flows are a vital part of the experiment."
The 1996 test flows were designed to attempt to mobilize sediment in deep pools in the river bottom to achieve the same result. Studies by USGS scientists over the past six years demonstrated that while high flows work to rebuild beaches and sand bars, the 1996 experiment scoured the upper reaches of the Canyon to rebuild beaches further downstream.
"By timing the high flow test to correlate with sediment inputs from the Paria River, which is about 16 miles downstream of Glen Canyon Dam, the sediment supply for rebuilding beaches would be increased," Wirth said.
Because the past drought year failed to produce sufficiently sized monsoon storms, the high flow test will not be done this year. Wirth said that portion of the experimental program will carry over into 2004.
The second aspect of the experiment relates to endangered fish species. Scientists have recognized that the humpback chub population has been in a general decline since highly fluctuating flows were curtailed in November 1991.
"Those flows helped keep the non-native fish — especially the rainbow and brown trout — in check," Wirth said. "The trout are thought to prey upon, and compete with native fish such as the endangered humpback chub."
As a result, high fluctuating flows are set to begin this month and continue through March to disrupt the spawning and survival to adulthood of the non-native trout.
"In addition to benefiting the native fish, a secondary purpose of the experiment is also to improve the quality of the Lee’s Ferry trout fishery by reducing the density of rainbow trout immediately below the dam," Wirth said. "The result should be larger, healthier fish in that Lee’s Ferry stretch — a fishery valued by the State of Arizona in the millions of dollars each year."
Finally, the experiment includes mechanical removal of non-native fish, primarily rainbow and brown trout, near the confluence of the Little Colorado River and the mainstream Colorado River.
"The effort will involve using electro-fishing techniques on the non-native fish and then removing them to reduce their population," Wirth said.
The removal and death of trout was a sensitive issue, especially to Native American tribes. The confluence of the Little Colorado and Colorado rivers is an area that is spiritually significant to the tribes, as are the lives of the fish themselves.
"Through government-to-government consultations with the tribes, reclamation, the Park Service and USGS were able to address those concerns," Wirth said. "The Haulapai tribe will return the trout to the earth as fertilizer in garden areas."
The fishery portion of the experimental program will take place over two years, with similar flows also taking place during January-March, 2004. The sediment portion of the experiment will take place when Paria River sediment inputs occur.
The experimental flood project went through the environmental assessment process, which resulted in the release of a "no significant impact" document. The BLM, USGS and National Park Service jointly prepared the EA.
The plan received the endorsement of the scientists who serve as the Science Review Panel to the Adaptive Management Program. The Adaptive Management Program is a collaborative effort that offers recommendations to the Department of the Interior on the operation of Glen Canyon Dam and other management actions to protect downstream resources.
The program includes stakeholders representing federal, state, and tribal governments, environmentalists, electrical power users and recreationists.