Controlled Flood to Replenish Grand Canyon

Early Tuesday morning Interior Secretary Bruce Babbitt plans to stand on a catwalk at Glen Canyon Dam, turn a valve, pull a lever and unleash a flood into the Grand Canyon.

Tons of water will wash down the Colorado River, raising its level as much as 10 feet. Trees will be uprooted. Some creatures will be washed away. And if all goes as planned, the river and the canyon will be better off as a result.

Below the dam, the Colorado is still a tumultuous river with its legendary rapids intact. However, the dam has transformed its warm, muddy flow into a cold, clear stream released from the depths of Lake Powell, upsetting the natural balance of the canyon. But as the cascading water surges downstream Tuesday, the river will get some of its old life back, and the history of western river management will take a new turn.

“We are finally putting conservation on a par with other needs,” said Paul Bledsoe, a spokesman for the U.S. Bureau of Reclamation, which operates most of the large dams in the western United States.

“For the first time at any dam, we are going to re-create seasonal flood conditions to rebuild beaches and protect natural habitat.”

There are no homes or crops inthe path of the rising water. Just below the dam lies the rugged terrain of Grand Canyon National Park. The flood will exhaust itself 292 miles downstream in Lake Mead, behind another, bigger dam.

Still, the discharge of nearly 120 billion gallons of water over seven days--enough to supply the city of Los Angeles for nearly seven months--amounts to a bold experiment. In dramatic fashion, it will test the notion that by imitating nature humans can begin to repair the environmental damage done by their big dams.

Since it was completed in 1963, Glen Canyon Dam has existed primarily to serve the electrical power requirements of millions of people in six western states. The daily manipulation of river flows to serve fluctuating power demands has taken a harsh toll on the Grand Canyon.

Two species of fish--the Colorado River squawfish and the bonytail chub--have disappeared and two others are endangered. New species of introduced fish have taken to the colder river. The murky, rust-colored water that gave the Colorado (which means “reddish brown” in Spanish) its name runs clearer now, its life-giving nutrients trapped in the sediment piled up behind Glen Canyon Dam.

Without the natural floods that used to wash down the canyon most years, pools that once sheltered a variety of aquatic life have filled in with debris and vegetation.

“The canyon and its native creatures evolved in a highly silted, warm water river that saw annual flood events,” said Pamela Hyde, director of Southwest programs for the environmental group American Rivers.

Representatives of the power industry have expressed concern that the experimental flood will mark the onset of a new, more costly era in water management. They say it wastes money to release more water than the power turbines can handle, or to send too much water through during the hours when electrical demand is low.

For others, the torrent of water roaring out of the dam Tuesday will signal the beginning of a long overdue healing process. Just as fire can cleanse and regenerate a forest, a flood can scour and stimulate a river canyon.

*

“River systems need to be disturbed,” said Bureau of Reclamation scientist Gordon Lind. “When you put a dam on a river, you cut down on the flooding and other dynamic changes that keep things healthy.”

Of greatest concern to people who explore the canyon are the eroding beaches and sandbars. They have been washing away as the sediment trapped in Lake Powell no longer replaces sand that is carried away by the river’s flow.

The beaches are a human foothold at the bottom of this mighty rift in the Colorado Plateau. They are vital to a $22-million-a-year river rafting industry that has taken half a million visitors through the gorges and rapids of the Grand Canyon.

Grooved into the base of dripping sandstone and granite walls, sheltered by feathery tamarisk trees, the fraying ribbons of sand are the only flat land along much of the river. For rafters, the beaches are the only places to comfortably camp.

“Over the long term, the canyon could be rendered inaccessible,” said Rob Smith of the Sierra Club’s Flagstaff, Ariz., office.

As the beaches peel away from canyon walls, exposing them to the action of the water, other treasures become vulnerable.

Surveys have found 3,500 archeological sites in the Grand Canyon, including Native American dwellings, ceremonial gathering places, fragments of pots and tools and other artifacts. As the canyon walls lose their footings and banks collapse into the river, experts fear, many of the 475 ruins near the Colorado may disappear with them.

For more than a decade, scientists have been trying to figure out the best way to stabilize the beaches. Since 1991, the daily rates of flow from the dam have been modified in an effort to cut down on erosion.

But those steps did not begin to rebuild the beaches, and that is what government experts hope to start doing.

If the experiment works, the flood will stir up what is left of the sediment on the river bottom--an estimated 12 million tons of sand--and deposit much of it on beaches in the canyon.

But just any old flood won’t do.

Too much water moving too fast will simply wash the sand down to Lake Mead. Too little water won’t stir up the bottom enough.

*

Bureau of Reclamation officials who control the water coming through the dam began slowly increasing the flow Friday. According to the plan, by Tuesday morning the dam’s power-producing turbines will be handling all the water they can--about 30,000 cubic feet per second. After Babbitt opens the huge overflow tubes, the outflow will reach 45,000 cubic feet per second--enough to fill the Rose Bowl in 7.2 minutes.

That rate will be maintained for seven days and then gradually reduced.

Glen Canyon Dam has let out more water in the past. In 1983, after a heavy runoff, Lake Powell threatened to crest the dam, and water was released at a rate of more then 90,000 cubic feet per second.

The slowly rising water level this week is not expected to pose a danger to hikers or rafters, say National Park Service officials, who do not plan to restrict travel in the Grand Canyon during the flood.

Bureau of Reclamation officials are expecting more than 100 scientists in the canyon to observe. “They’ll be in boats and helicopters and hanging off the walls,” said David Wegner, the bureau’s head of environmental studies at Glen Canyon Dam.

If the experts conclude that the experimental flood has been a success, government officials say they will seek to stage similar events every few years.

Among the onlookers will be scientists working for the Colorado River Energy Distributors Assn., a group of 100 utilities that buy much of their electrical power from Glen Canyon Dam.

Joe Hunter, the association’s executive director, said the bureau’s efforts to adjust flows to protect the downstream environment will reduce the dam’s electrical output 25% and incur $100 million in extra costs over 10 years.

He said the flood will contribute to those extra costs.

Water for hydropower is not used efficiently if it is expended during hours when it is not needed to meet consumer demands. Even when it is running at peak capacity, generating 1,300 megawatts of power, Glen Canyon Dam won’t be able to use all the water that will be coming through when Babbitt throws the switch.

But Hunter said his association won’t necessarily come out against future floods.

“We have taken the position that we will live by the science,” he said. “If science supports the idea of periodic flood flows, we will accept the verdict.

“But we want to make sure it’s the right decision, and that’s why our scientists will be there monitoring the effects of this particular flood.”

(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)

Flooding the Grand Canyon

Glen Canyon Dam interrupted seasonal flooding of the Colorado River and the natural deposit of silt in the Grand Canyon. A week-long artificial flood to be released Tuesday aims to restore vital sand bars and beaches by churning up sediment from the river bed. Flood waters will deposit the bottom sand on banks in the Grand Canyon before reaching Lake Mead, 292 miles downstream.

Before the Flood

Sand builds up on the river bottom, instead of on the banks.

After the Flood

Rushing water churns up the sand and leaves it on the banks as the flood recedes.

Source: U.S. Department of the Interior