Dam Limits Loosened to Feed Grand Canyon Matt York/Associated Press Periodic flow increases at the Glen Canyon Dam, on the Colorado River, will help replenish sediment in ecosystems downstream. The Interior Department announced a plan on Wednesday to allow periodic increases in the flow of Colorado River water through the Grand Canyon, alleviating the environmental disruption caused by the construction of the Glen Canyon Dam in Arizona in the 1960s. The secretary of the interior, Ken Salazar, said the plan would allow the river's managers to release excess water - more than twice as much as average flows - through and over the hydroelectric dam at will to help propel silt and sediment downstream into the canyon. By mimicking the river's original dynamics, Interior Department officials said, the flows could help restore the backwater ecosystems in which native fish are most at home. The goal is partly to enhance sandbars that create backwaters for an endangered fish, the humpback chub. The excess sand also nourishes beaches used by wildlife, hikers and rafters. Environmental groups like the Grand Canyon Trust strongly support the high-flow releases, which have been carried out experimentally three times before, most recently in 2008. In a telephone news conference, Mr. Salazar said the releases would be timed for when storms or snowmelt have carried large amounts of silt just downriver from the dam. The first high-flow release under the new protocol will probably come this fall, he added. "The triggering conditions are related to the amount of sediment in the system," he said. When heavy rains occur in the Paria River watershed, which drains rocky territory in southwestern Utah, they frequently flush tons of silt into the Colorado, which the Paria meets below the dam. The flexible flow plan will remain in effect through 2020. While normal flows through the turbines of the Glen Canyon Dam range from 8,000 to 22,500 cubic feet per second, the high-flow events could reach 45,000 cubic feet per second and last anywhere from one hour to four days. At the highest flow, there is too much water to go through the hydroelectric turbines, and the excess is funneled over the dam. Anne Castle, assistant interior secretary for water and science, said in the news conference that the delivery of power to the six million customers served by the dam would not be significantly affected. The department also announced plans to change its management of nonnative trout in the river. The agency has been killing nonnative trout, which crowd out the humpback chub, at sites along the Colorado. The practice brought protests from American Indian groups, including the Zuni tribe, for whom these areas are sacred, Interior Department officials said. The new plan, described as experimental, instead envisions "live removal" of the trout for restocking in other waters, Ms. Castle said. "We're trying to understand better the impact of those changes on the nonnative fish that are being removed and on the endangered fish," she said.