The O'Shaughnessy Dam is a curved gravity dam on the Tuolumne River in the Hetch Hetchy Valley of California's Sierra Nevada. The dam is located in Yosemite National Park, and creates the Hetch Hetchy Reservoir. It is named for former San Francisco chief engineer and the original chief engineer of the Hetch Hetchy Project Michael M. O'Shaughnessy.
The dam provides water and electricity to 2.4 million people in the city of San Francisco, San Mateo County, Alameda County, and the San Joaquin Valley. The power-generation facilities and transmission lines are concealed to protect the valley's famous scenery. Paul James Ost was the electrical engineer put in charge of power operations and electrical engineering phases of the Hetch Hetchy project. The hydroelectric plant generates about 500 megawatts, or 0.2 percent of California's power use. The reservoir holds 0.444 cubic kilometers (360,360 acre-feet) of water, of which about one-third is diverted into Canyon Tunnel and the Hetch Hetchy Aqueduct to the San Francisco Bay Area.
The O'Shaughnessy Dam is near Yosemite's western boundary, but the long, narrow, fingerlike reservoir stretches eastward for about 12.5 km (over 8 miles).
The Sierra Club currently advocates removing the dam, but the city of San Francisco opposes, because the reservoir currently serves 2.4 million people, including parts of San Mateo County, Alameda County, and Silicon Valley. Deconstructing the dam would cost billions of dollars, according to a study ordered by Governor Schwarzenegger.
In 1987, the idea of razing the O'Shaughnessy Dam gained an adherent in Don Hodel, then Secretary of the Department of the Interior under President Ronald Reagan. Hodel called for a study of the effect of tearing down the dam. The National Park Service concluded that two years after draining the valley, grasses would cover most of its floor and within 10 years, clumps of cone-bearing trees and some oaks would take root. Within 50 years, vegetative cover would be complete except for exposed rocky areas: eventually a forest would grow, rather than the meadow being restored.
Some observers, such as Carl Pope (Director of the Sierra Club), stated that Hodel had political motives in proposing the study. The imputed motive was to divide the environmental movement: to see residents of the strongly Democratic city of San Francisco coming out against an environmental issue. Dianne Feinstein, the mayor of San Francisco at the time, said in a Los Angeles Times story in 1987: "All this is for an expanded campground? ... It's dumb, dumb, dumb." Hodel, now retired, is still a strong proponent of restoring Hetch Hetchy Valley and now-Senator Feinstein is still strongly against restoration. The Bush Administration has proposed allocating 7 million dollars to studying the removal of the dam in the 2007 budget. Dianne Feinstein opposed this allocation, saying "I will do all I can to make sure it isn't included in the final bill. We're not going to remove this dam, and the funding is unnecessary.