For almost three decades, the Glen Canyon Dam on the Utah-Arizona border has tamed the once-wild Colorado River.
Now, the U.S. Bureau of Land Management wants to open the dam's gates next April, sending what would amount to a moderate flood down river.Jack Schmidt, an expert on the Colorado River and assistant professor at Utah State University's department of geography and Earth sciences, said the idea is to restore natural conditions along the river.
"When you talk to early river runners, one of the notable attributes of the Grand Canyon landscape was big, expansive, open sandbars," he said.
By blocking the floods that once scoured the region, Glen Canyon Dam has allowed thick stands of salt cedar trees to invade riverside sands.
The river's heavy load of sediment now dumps into Lake Powell rather than continuing downstream. As a result, the Colorado slowly is washing away its banks and sandbars. Schmidt estimates they have declined by up to 40 percent since the mid-1960s.
"I would argue the removal of one of the landscape elements is a fundamental change in the canyon's landscape," he said. "It isn't any different from someone saying, `Let's remove the coconino sandstone layer and the canyon still will be almost as deep."'
The dam-induced changes also have reduced habitat for the endangered humpbacked chub - a species of fish found only in the Colorado - and eliminated many of the campsites once used by people floating through the Grand Canyon.
Schmidt said the changes have not been all bad. The salt cedar trees, for example, have provided additional habitat for two rare birds, the Southwestern willow flycatcher and Bell's vireo.
What is more, the cold, clear water released from Glen Canyon creates ideal trout habitat along a 15-mile stretch of river below the dam.
Nonetheless, the BOR has decided to modify its operations of the dam to partially mimic natural conditions in the Grand Canyon - including the restoration of yearly floods.
When the Colorado was wild, it carried an average of 66 million tons of sediment each year into the head of the Grand Canyon. After the dam was built, the river carried 91,000 tons of sediment annually.
Glen Canyon Dam has blocked the spring floods that once built river banks and sandbars. Most of the sediment sits at the bottom of the river channel.
Hence, the BOR's decision. Officials hope the resulting floodwaters pick up the sand and mud and redeposit it on river banks and in backwaters, eventually creating new beaches and sandbars.
Plans for this manmade flood have been controversial, with threats of lawsuits stalling an attempt to do it last spring.
Still, Barry Wirth, spokesman for the BOR's upper Colorado region, says most of the obstacles have been overcome, and "we're moving ahead toward a spring event" in 1996.
Schmidt said the plan is to release from Glen Canyon Dam 45,000 to 50,000 cubic feet per second of water for as many days as the BOR can provide it. This will likely be about a week.
The flood will be about twice the normal maximum flow during the past several years, but far below the size of pre-dam floods that often exceeded 100,000 cfs.