Water Education Foundation

The Hetch Hetchy Aqueduct

Posted by: Aquafornia on August 19, 2008 at 3:50 pm

The Hetch Hetchy system delivers about 265,000 acre-feet of pristine Sierra Nevada water per year, providing for about 80% of urban uses for San Francisco, as well as parts of San Mateo, Santa Clara and Alameda counties. The Hetch Hetchy system consists of 11 reservoirs, numerous water conveyance pipelines, and water treatment facilities. The system also generates over 2 billion kilowatt hours per year of hydropower.

The plan was first proposed in 1902, but due to the inclusion of the Hetch Hetchy Valley within the boundaries of Yosemite National Park, the project faced complications and stiff opposition. It finally won congressional approval with the passage of the Raker Act in 1913, which specifically authorized the project. The Hetch-Hetchy project was the first completed project to take water that would have otherwise flowed into the Delta and divert it for consumptive use by piping the water across the Delta to the Bay Area.

The O'Shaughnessy Dam was built in 1923, and raised in 1928. It is used for water storage, hydropower generation, and provides some flood control. Plagued by financial delays and difficulties in tunneling through the Coast Range, the first water from the project did not reach the San Francisco peninsula through the 150-mile aqueduct until 1934.

The watershed that feeds the Hetch Hetchy system is located within national park boundaries, a pristine wilderness that is virtually untouched by human influences. Water from the O'Shaughnessy Dam is of the highest quality, earning a “filtration avoidance status” from the federal government; this means the water meets drinking water quality standards and requires minimal treatment. It is only one of about a half-dozen water sources nationwide to have this designation.

In recent years, there have been calls to remove the dam and restore the Hetch Hetchy Valley, said to be a twin of the neighboring Yosemite Valley, and perhaps even more beautiful back before it was flooded. There are valid arguments both for and against the dam. Proponents of dam removal question why a reservoir is allowed within a national park, and argue that a restored Hetch Hetchy Valley would provide more park space to one of the nation's most visited parks. Opponents of dam removal cite the loss of hydropower as a significant source of clean energy, as well as income to pay operating expenses. In addition, the loss of the pristine water impounded behind the dam would increase treatment costs to the system and ultimately the users. They also argue that removing the dam would not benefit any endangered species and would have only minimal ecological benefits.

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Special thanks to Jerry Pierce for the use of the picture of the Hetch Hetchy pipelines.

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