Impact of dam flooding to be tested

Published: Sunday, May 27 2012 10:00 p.m. MDT

The government plans to simulate natural flooding from the Glen Canyon Dam without harming power needs.

Tom Smart, All

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FLAGSTAFF, Ariz. — The federal government has approved two programs to further test the impact of flooding the Colorado River through the Grand Canyon and to help boost the native fish population.

Since the 1960s, Glen Canyon Dam near the Arizona-Utah border has blocked 90 percent of sediment from the river from flowing downstream, turning the once muddy and warm river into a cool, clear environment less suitable for native fish like the endangered humpback chub. It also has impacted hydroelectricity, beach recreation and archaeological sites.

The Interior Department announced Wednesday that it has signed off a program for more high-flow releases through 2020 that will simulate natural flood conditions, while meeting water and power needs. The second focuses on protecting native fish from nonnative predators and improving habitat.

"It represents a more finely turned balance of the resources represented in the Colorado River," said Anne Castle, assistant secretary for water and science. "We're marking a milestone. … This is a huge step in the right direction."

Interior Secretary Ken Salazar had called for more man-made floods along the 277-mile stretch of the Colorado River through the Grand Canyon. High flow releases in 1996, 2004 and 2008 built up the sediment in the river, providing a habitat for plants and animals, building beaches for campers and river runners, and helping protect archaeological sites from erosion and weather. But the results have been short-lived, and the sandbars eroded within months.

The 1996 flood also likely led to an increase in the number of nonnative rainbow trout that eat humpback chub. The latest flood sent enough water through the Colorado River to fill 108,000 Olympic-sized swimming pools, and also unexpectedly boosted the trout population.

Salazar said the U.S. Bureau of Reclamation, which operates the dam, will take what it's learned from those floods and apply it to further releases that will be timed to follow natural deposits of sand from tributaries of the Colorado River downstream from the dam.

The Paria River, about 16 miles downstream, and the Little Colorado River provide 10 percent of the historic sediment that was deposited in the Colorado River. Two-thirds of artificial floods would occur in the fall if they were timed to follow the natural deposits of those tributaries, the U.S. Geological Survey has said.

"If the new high-flow experiments don't work, we'll change them," Salazar said. "But the plan allows for that flexibility."

The amount of water released from the dam that powers millions of homes in the Southwest won't change, but the timing would. The Bureau of Reclamation said the artificial floods would happen between March and April, or October and November, ranging from one to 96 hours.

During high-flow experiments, water bypasses the dam, which could mean a loss of up to $122 million for the hydropower industry over 10 years, according to the Bureau of Reclamation. Power companies would have to make up for that loss elsewhere.

Leslie James, executive director of the Colorado River Energy Distributors Association, said she would favor high flows in the fall because previous springtime floods have proven harmful to the humpback chub.

"The devil is in the details on how those are implemented — frequency, duration and timing," she said.

Sam Jansen, of Grand Canyon River Guides, praised the longer-term plan as a good way to maintain sandbars that draw campers and others to the shores of the Colorado River.

"It seems like the best thing we can do right now without sediment augmentation," he said.

The National Park Service and the Bureau of Reclamation also have been working on a long-term management plan for the dam, which will incorporate the research and experimental programs announced Wednesday, Castle said.

To control nonnative fish, the Bureau of Reclamation says it will remove trout from the river and stock them in waters for sport fishing. The agency once proposed shocking the water to separate out the nonnative fish, and then euthanize and freeze them for either human consumption or as food for captive wildlife. But that plan was changed over concerns from American Indian tribes who consider any life in the Grand Canyon sacred.

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