When a dam slices through this moving ecosystem, it slows and warms the water.
In the reservoir behind the dam, lake creatures and plants start to replace the former riverine occupants.
Gordon Grant points out that on the Columbia River, people fished at Celilo Falls for thousands of years, making it one of the oldest continually inhabited places in the country.
The falls are now covered in 100 feet of water at the bottom of the reservoir behind the Dalles Dam.
Sediment eddies and drops to the bottom, rather than continuing downstream.
Migratory fish can be visceral reminders of how a dam changes a river.
A haphazard mound of earth was the only thing holding back the rising waters of the Sandy River. Soon the river punched through, devouring the earthen blockade within hours. Forest Service, was part of the team of scientists and engineers who orchestrated the removal of Marmot Dam.
Later, salmon would swim upstream for the first time in 100 years. Armed with experimental predictions, Grant was nonetheless astonished by the reality of the dam’s dramatic ending.
This became the PNJ Interchange, “the seed of the electricity grid as we know it,” explains Martin Doyle, a professor of river science and policy at Duke University.As the ecological and cultural toll dams take became clearer, our relationship with them started to show its cracks. At the turn of the century, John Muir and a small band of hirsute outdoorsmen opposed construction of the O’Shaughnessy Dam in the Hetch Hetchy Valley of Yosemite. By the 1960s, pricy full-page ads in the New York Times opposed the Echo Park Dam on a tributary of the Colorado. Echo Park Dam was never built—but downstream, Glen Canyon Dam went up instead, inspiring new levels of resentment and vitriol among dam opponents.In a 1975 novel by cantankerous conservationist Edward Abbey, environmental activists blow up Glen Canyon Dam.Now, demand for power in Las Vegas and Phoenix regulates the flow.
“They turn the river on when people are awake and turn the river off when people go to sleep,” explains Jack Schmidt, a river geomorphologist at Utah State University.
Without “gangbuster” spring floods, he says, the sandbars are disappearing and the archaeological sites are increasingly more exposed.