Grand Canyon controlled floods: Ecological benefits vs. lost revenue


Grand Canyon controlled floods: Ecological benefits vs. lost revenue

Brian and Ann Blue and their dog, Rosean, watch the 2010 spring torrent at Grand Falls cascade down into the canyon of the Little Colorado River. (Mark Henle/The Arizona Republic)

Posted 03 July 2011, by Staff, AZcentral (The Arizona Republic),

The issue: Controlled floods through the Grand Canyon could help restore the natural flows and ecology of the Colorado River.

When Glen Canyon Dam was built in the early 1960s upstream from the Grand Canyon, it stopped sediment from flowing downstream and lowered the water temperature. The river became less hospitable for native wildlife and for hikers and boaters as it washed away beaches and backwater habitat without replacing the sand as it once did.

Current events: In 1996, the federal government began experimenting with controlled floods, releasing high volumes of water from the dam in an attempt to mimic, at least briefly, the river’s natural flows and move sand and sediment downstream. The government conducted three floods, in 1996, 2004 and 2008.

The U.S. Bureau of Reclamation has now proposed a regular schedule of controlled flows starting this year and continuing through 2020, timed to take advantage of sediment deposited at the mouths of several tributaries to the Colorado.

What’s at stake: One of the lessons of the first three floods was that the effects are short-lived. The river requires constant attention, with more-frequent floods and monitoring, said Martha Hahn, chief of science and resource management at Grand Canyon National Park.

“It’s not the high flows themselves; it’s what you do in between that’s important to the resources,” she said.

Scientists need to watch what happens along the beaches, in the habitats and to the native species, such as the endangered humpback chub. Using an adaptive management, or “learning by doing” approach, researchers can react to the effects of each flood. Scientists have learned that the 2008 flood helped the survival of non-native rainbow trout, a predator of young humpback chub.

The amount of sand brought in by tributaries is also critical, researchers found. The high flows not only leave sand along some stretches of the riverbank, they can wash it away along others. If there is too little sand and sediment to begin with, the benefits could be eroded away.

The experimental floods have caused problems for power companies that buy and distribute electricity generated by Glen Canyon Dam. A limited amount of water can be released each year from the dam, based on agreements among the seven states that rely on the Colorado River. When higher volumes are released all at once, less water is available for power production at other times of the year, resulting in lost revenue. The Western Area Power Administration, which markets and delivers electricity from Glen Canyon, estimated that changes in operations at the dam since the experiments began have cost power companies and customers about $50 million a year.

What’s next: Federal officials could conduct a controlled flood as early as this fall.


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