The half-mile-long Imperial Rapid, submerged for three decades, had re-surfaced. The natural draining of the nation's second largest reservoir was under way, but how far would it go, we wondered?
Climate change in the region has lowered the reservoir 120 feet over the past five years. This drop should have been sufficient to expose half the remaining 21 rapids that were also submerged by the reservoir, yet only Imperial has come out so far. A look around from the raft revealed the problem: We were floating through a massive slab of sediment that had built up in the decades since Glen Canyon Dam was finished.
The remainder of our descent was through a ditch framed by gray cliffs of sand rising 25 feet on either side, with dump-truck-sized chunks calving off like icebergs every 15 minutes or so.
The ditch widened as we caught up with the slack water of the reservoir, now 30 miles below Imperial Rapid, but still 140 miles from Glen Canyon Dam. The lower water levels here, and on the edges of much of the rest of the reservoir, have re-exposed many of the cliffs, spires and canyon walls that John Wesley Powell dramatically described on his 1869 exploration of Glen Canyon.
Although Lake Powell reservoir is just 40 percent full and has lost 50 percent of its surface area, it has dropped only 20 percent in elevation. The reservoir is still 445 feet deep near the dam. It’s like a wide funnel: There's more water stored at the top. But scientists predict that it will fall more rapidly if present climatic conditions persist.
The reservoir's elevation could also drop three times faster over the next three years than it has over the past five. If that happens, it would cause hydroelectric power production at the dam to cease in 2006. By 2007, a condition known as "dead pool" would be created, which means that the dam, for all practical purposes, would become useless as a power generator. The reservoir, however, would still stretch 104 miles upstream, contain approximately 2 million acre-feet of water and sediment, and rest 234 feet above the original river bed at Glen Canyon Dam.
Still submerged would be most of Glen Canyon's 125 signature side canyons, which inspired the canyon's pre-dam river runners along with the mounting numbers of present-day advocates for Glen Canyon's restoration. Nature's crash course in water scarcity is helping to amplify the mounting economic and environmental liabilities associated with Glen Canyon Dam and Lake Powell, raising the prospect of decommissioning the dam and uncovering the remainder of the canyon.
Glen Canyon Dam was completed in 1963, as a water-storage facility for downstream users. Because of other storage facilities built in the basin, principally Lake Mead behind Hoover Dam, it will be this winter before Lake Powell's storage will, for the first time, actually contribute to downstream water use.
Over the years, Lake Powell will have lost 40 million acre-feet of water from evaporation and seepage, while providing only 23 million acre-feet in storage. This lost water represents nearly three years of the entire annual flow of the Colorado River. It’s not surprising that people are looking for more efficient ways to save this valuable water. California, Nevada and Arizona are already doing so by storing Colorado River water in underground aquifers. They lose as little as 1 percent of the water to the environment, compared to the over 60 percent of water that is lost at Lake Powell.
Concern is also mounting over the damage Glen Canyon Dam is causing to the downstream ecosystem in Grand Canyon National Park. Four of the Canyon's eight native fish are already gone, as are otters, muskrats and a host of birds, insects and reptiles. Despite more than $200 million invested in efforts to mitigate the dam's impacts, biologists say these declines will continue.
As the drought continues, a growing number of scientists are questioning whether there will ever be enough water to fill Lake Powell. But I have a different question: Once the reservoir dies a natural death, shouldn’t we finish the job and let the river run again?
John Weisheit is a contributor to Writers on the Range, a service of High Country News (hcn.org). He is conservation director for Living Rivers, a nonprofit group in Moab, Utah.
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