One of Yosemite's dams is probably doomed.
Even as officials debate expanding Tuolumne County's Lyons Reservoir, Yosemite National Park officials want to remove one of theirs.
The Cascades Diversion Dam, which powered Yosemite Valley with electricity from 1917 to 1985, could be removed as soon as this fall. Eighteen feet tall and 184 feet wide, the dam sits in the Merced River in Yosemite Valley, near the intersection of El Portal and Big Oak Flat roads.
"This isn't just any river anywhere. This is the Merced River, a wild and scenic river, in Yosemite National Park," said Ranger Deb Schweizer.
The dam took a year to build in 1916.
O'Shaughnessy Dam at Hetch Hetchy Reservoir went up about the same time, and the two projects often competed for workers.
The diversion dam, made of redwood planks, boulders and concrete, replaced the hydropower plant at Happy Isles, said Civil Engineer and Project Manager Michael Pieper. The dam went offline in the winter of 1985-86, and Pacific Gas & Electric now supplies the valley's power.
But now the diversion dam needs fixing, which could be more expensive than simply pulling it out. Because of the river's designation, officials aren't even sure they would be allowed to do what's needed probably replacing the structure with a new dam.
Park officials are reviewing the dam's Environmental Impact Statement, which lists three alternatives for the structure's future. Two propose taking the dam out, while the third suggests leaving the site as is.
Despite California's energy crisis, park officials said safety, cost and effort prohibit their putting the dam's potential power back on-line.
Leaving the dam in its current state is just not safe, Pieper said.
Visitors could fall walking across the deteriorating redwood planks. Debris could break off the boulder-and-concrete structure and hurt a fisherman downstream. Or, in a major flood, the whole dam could blow out.