For a few days Grand Canyon National Park's chief of science and resource management, Martha Hahn, floated down mile after mile of Colorado River, marveling at aquatic habitat and shoreline that looked and acted like the Glen Canyon Dam never existed.

"You felt like the system was more alive — you felt an urgency in the system," Hahn said in an interview Friday. "You felt a real aliveness, but a real calmness, to the system. It felt very natural. You almost felt like you were a pioneer back in the days after a flood came along."

But the Glen Canyon Dam does exist, and the flood Hahn referred to was part of a high-flow release of up to 41,500-cubic-feet-per-second of water from the dam during an almost three-day experiment that started March 5.

Hahn and others hopped on the once-clear, now milky river March 6 and traversed about 80 miles of the Colorado, camping along its shore and monitoring the early effects of what was the third such high-flow experiment since 1996. By March 9 Hahn saw what she had hoped would happen on the Colorado below Lee's Ferry, which is about 15 miles south of the dam and Lake Powell.

"We began to see the amount of sediment that was being deposited," she said. "We could tell it was just laden with sediment."

And that was the intent of the experiment, to lift what was three times the amount of sediment from the river bottom, compared to the last experiment in 2004, and move it downstream to create or rebuild sandbars and beaches for wildlife and river runners. Another anticipated benefit of depositing all of that sand along the shore is to help preserve exposed, eroding archaeological sites.

Hahn described how sandbars that never existed had been formed and how backwaters were created that are critical to the survival of the federally endangered humpback chub fish. Signs of beaver and bighorn sheep activity showed up in the new sand as the water level receded.

"You could see these perfect tracks going right into the water," Hahn said. "The animals just adapted and moved right in."

How the Bureau of Reclamation operates the dam and its daily fluctuations at this point, she added, will determine whether the benefits of the experiment can be sustained. Monsoonal rains that should start in July in areas of tributaries that feed into the river and a more steady flow from the dam starting in September are also part of the sustainability equation.

On Friday, Interior Secretary Dirk Kempthorne announced the release of the 2008 Annual Operating Plan for Colorado River reservoirs and distribution of river water to Arizona, Nevada and California, addressing in particular lower basin shortages.

Kempthorne said in a statement that the plan directs river management "to protect and conserve its water supplies for current and future generations." For the 2008 water year that began last October, the plan calls for a release of 8.23 million acre-feet of water from Lake Powell through the Glen Canyon Dam. If there's enough water Sept. 30 in Lake Powell, which after a good snow season is supposed to rise by 50 feet, additional water will be released from the dam to equalize amounts in Powell and Lake Mead.