By Jen Beasley
Friday, January 18, 2008 2:36 AM CST
| The Grand Canyon has a sediment impediment. But perhaps not for long. A March release of 45,000 cubic feet of water from Lake Powell down the Colorado River is expected to be announced soon by the Secretary of the Interior. The flood is designed to push silt at the base of tributaries below Glen Canyon Dam downriver in an effort to restore the lower basin of the Colorado to a more natural ecosystem. It would be the third such attempt at rebuilding sediment-based sandbars downriver made by the Glen Canyon Dam Adaptive Management Program, which seeks to manage the dam that reigned in the Colorado in 1963, flooding the Utah-Arizona border with the nation’s second-largest reservoir and a wash of controversy. |
USU's Jack Schmidt (Meegan M. Reid/Herals Journal) |
A March release of 45,000 cubic feet of water from Lake Powell down the Colorado River is expected to be announced soon by the Secretary of the Interior. The flood is designed to push silt at the base of tributaries below Glen Canyon Dam downriver in an effort to restore the lower basin of the Colorado to a more natural ecosystem.
It would be the third such attempt at rebuilding sediment-based sandbars downriver made by the Glen Canyon Dam Adaptive Management Program, which seeks to manage the dam that reigned in the Colorado in 1963, flooding the Utah-Arizona border with the nation’s second-largest reservoir and a wash of controversy.
Dr. Jack Schmidt, a USU professor and contracted adviser to the program through the Grand Canyon Monitoring and Research Center, said since the construction of the dam, 98 percent of the sediment that used to flow downriver has been trapped in the bowl of Lake Powell, and the lack of silt movement has compromised the ecosystem of the Colorado.
“The two significant environment resources along the river that are of the greatest concern in Grand Canyon National Park are a population of fish called the humpback chub, and then the other is sandbars,” Schmidt said.
Sandbars are important because they serve as habitat for the nurseries of native Colorado River Basin fish, including the endangered humpback chub.
The destruction of habitat has already caused three species of native fish to disappear from the Colorado River, Schmidt said, as they have been overtaken by introduced species such as rainbow trout.
Schmidt said sandbars also support the growth of riverside plant life, and they create recreation opportunities by forming places for people to camp along the river. But in the absence of the natural flow of the Colorado, Schmidt said these vital sandbars don’t get replenished.
“This is all about sediment being a good thing,” Schmidt said.
It is in an effort to restore all of these benefits of sediment that the GCDAMP is planning the flood. But it may be the last gasp for this strategy, which has shown mixed results in the past.
Schmidt said the first such flood in 1996 was an “ambiguous success.” He said that release of water did build sandbars, but because it lasted for seven days, it also eroded existing ones.
In terms of science, Schmidt said, it was a “fabulous success” because they learned from the experiment that there was not enough sediment below the dam to sustain a flood of that length. But from a management perspective, “We did more harm than good.”
In 2004 it was tried again, this time with a three-day release. That try yielded an accumulation of new sandbars, but it only showed in one 30-mile stretch of the river.
Schmidt said the only alternative to the flooding technique is to build an expensive sediment pipeline around the dam in order to deposit sand downriver. Such a pipeline would cost anywhere from $220-$430 million initially, Schmidt said, with an annual operating price tag ranging from $7 million to $17 million.
So if this flood doesn’t work, the GCDAMP will be dammed if they do and dammed if they don’t.
“It’s either make a big financial investment, or declare that the price paid for the construction of Glen Canyon Dam was the irreversible harm to the natural river ecology of Grand Canyon National Park,” Schmidt said.
Schmidt said there will also be losses to the hydroelectric revenues that can be garnered from processing the water in turbines instead, which is not done during these release due to mechanical constraints. The flood will not represent a loss of water, however, because the Upper Basin States of the Colorado River have an agreement with the Lower Basin States to send a certain amount of water downriver each year to Lake Mead, and the water released in the flood will count toward those required totals.
This time may be different from the other two because there is now more sediment available to move downriver, Schmidt said. The March flood will be another three-day effort so as to not wash away old sandbars, but will have more sediment at hand to make new ones because recent natural flooding of tributaries to the Colorado that lay below the dam have deposited large amounts of sediment available for the moving. But Schmidt said there is only a small window when the sediment deposits are at their peak to be moved, before they start to erode on their own. And the results won’t be fully analyzed for about another two years following the flood.
“That’s how science is,” Schmidt said. “It takes time.”
And solutions may be as tricky to construct as sandbars.