The National Parks Conservation Association expressed "grave concern" Thursday about the Bureau of Reclamation's five-year plan for "high-flow" releases on the Colorado River like the one that began this week at the Glen Canyon Dam in Page, Ariz.

With only one planned release for five years, NPCA southwest regional director David Nimkin said in a statement that the BOR's plan is short-sighted while ignoring the National Park Service's input and the need for more scientific research that would come from additional releases.

Secretary of the Interior Dirk Kempthorne started a 60-hour release from the dam Wednesday morning that will pump over 41,000 cubic feet per second of water from Lake Powell into the river.

The goal of the so-called high-flow experiment is to scour the river bottom of sediment and move it downstream to repair beaches and restore habitat along the way. Intended beneficiaries of the simulated flood are exposed archaeological sites, the federally endangered humpback chub fish and people who recreate on the 277 miles of Colorado River below the dam.

Similar experiments took place in 1996 and 2004. But only one, which started Wednesday, is scheduled for the next five years.

"It is irresponsible of the Department of Interior to ignore the environmental impacts this plan will have on the Grand Canyon for the sake of hydropower and other priorities," Nimkin said.

He was critical of the plan's lack of "follow-up floods," which he said would help ensure that the beaches and sandbars that are supposed to be repaired or formed can be sustained. Currently the BOR's plan is for steady releases, or lower-velocity flows than this week's release, from the Glen Canyon Dam in September and October in the years ahead.

Grand Canyon National Park's chief of science and resource management, Martha Hahn, earlier this week outlined a BOR plan that will rely on monsoonal rains that start showing up around July in the Glen Canyon. The hope is that, along with the experiment, the rains will help a Colorado River that has changed dramatically since the dam's completion in 1966. Results, if there are any, showing the intended impact of the BOR's plan, will be slow in coming.

"It just takes a long time to see nature react," Hahn said.

Overall, officials say the total amount being released from an already low Lake Powell through the dam this year will not change from last year. The experiment is expected to impact the lake level by one to two feet. But then spring runoff from an above-average snow season into tributaries that feed the Colorado above the dam are expected to raise the lake level by 50 feet.

Nimkin said a lack of additional high-flow events "could lead to impairment of the natural and cultural resources of Grand Canyon National Park." He also accused the BOR's plan of not appropriately responding to the Grand Canyon Protection Act and not complying with the 2006 Grand Canyon Management Policies.

The high-flow portion of the experiment is expected to end sometime late Friday. The river's level from the dam south will gradually recede and as early as Sunday the visual impacts of this week's experiment should start appearing. A team of 100 scientists from around the world will be studying the effects for months on fisheries and habitat in and around the Colorado below the Glen Canyon Dam.

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E-mail: sspeckman@desnews.com