"With the era of building big dams over in the U.S., a growing number of existing dams are being modified to produce hydropower. These projects, advocates say, avoid the damaging impacts of new dams and could generate enough renewable electricity for several million homes."
"In 1969, the U.S. Army Corps of Engineers finished construction of the Red Rock Dam on the Des Moines River in Marion County, Iowa. One of thousands of U.S. dams built that decade, its purpose was to moderate seasonal flooding, allowing the Corps to release the million-and-a-half acre feet of snowmelt it impounded each spring at will. And for more than 50 years, aside from providing locals with a reservoir in which to fish and go boating, that’s all it did.
That changed last fall when engineers let water rush into two penstocks freshly punched through the concrete structure of the dam. Flowing into a powerhouse below, the water spun two hydroelectric turbines before pouring back into the river, generating enough electricity to power more than 18,000 homes in Iowa, Minnesota, and North and South Dakota.
More than a decade in the making, the Red Rock project is the latest of 36 U.S. dams retrofitted to generate hydropower since 2000, representing more than 500 megawatts of renewable generation capacity. That’s just a fraction of the 33,000 megawatts of solar and wind energy capacity the United States added in 2020 alone. But these retrofits have been the primary source of hydropower development in the U.S. since the end of the dam-building booms of the 20th century. And with ambitious targets from states and the federal government to decarbonize much of the grid by 2035 to avoid the worst effects of climate change, hydropower and environmental advocates say retrofitting dams presents an opportunity to leverage existing infrastructure for renewable energy while avoiding the environmentally destructive impacts of new dams on rivers."