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But that sand is disappearing because the upstream Glen Canyon Dam traps most of the would-be replacement sand coming down the Colorado River.
Furthermore, snowmelt used to swell the river with monstrous spring floods, redistributing sediment throughout the canyon.
“There’s a lot of human history in the river corridor, and unfortunately a lot of it is being eroded away in the modern era,” East says.
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.
Grand Coulee Dam, which stopped the Columbia River in 1942, supplied vast quantities of electrical power that turned aluminum into airplanes and uranium into plutonium. They restrained rivers to control floods and facilitate shipping.