Past releases from Glen Canyon Dam haven't beefed up sandbars
By Patty Henetz
The Salt Lake Tribune
Article Launched: 12/12/2007 08:39:56 PM MST
LAS VEGAS - Flushing water through the Glen Canyon Dam to try to build up sandbars, beaches and backwaters hasn't worked in the past, but that's not a deterrent to federal scientists who want to try again.
Speaking during a meeting of the Upper Colorado River Commission, U.S. Geological Survey scientist John Hamill said plans are afoot to release 41,500 cubic feet per second of water from behind the dam into the river below for 60 hours.
The release would be a way to incorporate previous results from other experiments to try to find a way to sustain sand flow in a healthy way in the river to discourage exotic invasive vegetation and create safe harbors for species including the endangered humpback chub, said Hamill, chief of the USGS monitoring and research center in Flagstaff, Ariz.
The Upper Colorado River Commission, which manages the Colorado River rights for Utah, Montana [Wyoming], New Mexico and Colorado, met during the annual Colorado River Water Users Association meeting. The association includes the lower basin states - California, Arizona and Nevada - that have prior rights on the river and hold the balance of power over the entire river system's allocations.
The U.S. Bureau of Reclamation, which already has spent more than $200 million seeking ways to counter the dam's downstream damage, is actively planning for the release, even though a 2005 USGS report said 13 years of similar efforts had been unsuccessful.
Previous attempts have either blasted away the sand that had accumulated naturally from tributary inflow, or simply didn't deposit any sand. This time, Hamill said, the river below the dam is relatively sandy, and changes in Grand Canyon management have allowed warmer water and more sediments to flow through the dam.
The technique is called "adaptive management," kind of a learn-as-you-go series of experiments designed to run over the long term. The 2008 test would be a synthesis of previous experiments, including a test in summer 2000 where dam releases were kept at a steady 8,000 cubic feet per second from June 1 to Sept. 1.
Hamill said that resulted in water temperatures in backwaters and shallow shoreline habitats reaching about 50 degrees Fahrenheit - the river below the dam is usually about 20 degrees Fahrenheit [colder than the pre-dam river temperature]. The steady release also limited sand drift downstream and kept healthy a population of humpback chub that had been moved near the mouth of the Little Colorado.
Still, there's a limit to building up sandbars; it is only possible if there's already a lot of sand in the river - and there's not.
Scientists acknowledge that the tributaries that feed the Colorado River below the dam, such as the Paria and Little Colorado, don't provide enough sand to keep ecosystems healthy.
And as Lake Powell sediments become increasingly polluted, just sending them down-river isn't a good answer, either, said Living Rivers director John Weisheit. The only solution, he says, is to remove the dam.
Built in 1963, Glen Canyon Dam has provided water and power for the West. The sand-flow issue must be resolved - both because of the need for sandbars in the Grand Canyon, and because the buildup of sediment in Lake Powell will eventually threaten the reservoir and the functions of the already-impaired hydropower plant.
