| O'Shaughnessy Dam | |
|---|---|
&sq=Christopher R. Hill &lang=en&file=File:O%27Shaughnessy_Dam.jpg) | |
&sq=Christopher R. Hill &lang=en&file=File:USA_California_location_map.svg)  Location of the O'Shaughnessy Dam in California | |
| Location | Tuolumne County, California, U.S.[1] |
| Coordinates | 37°56′51″N 119°47′18″W / 37.94750°N 119.78833°W |
| Purpose | Water supply Hydroelectricity |
| Status | Operational |
| Construction began | August 1, 1919 |
| Opening date | July 7, 1923 |
| Owner(s) | San Francisco PUC |
| Dam and spillways | |
| Type of dam | Concrete arch gravity |
| Impounds | Tuolumne River[2] |
| Height | 430 ft (130 m)[3] |
| Length | 900 ft (270 m)[2] |
| Elevation at crest | 3,812 ft (1,162 m)[2] |
| Width (base) | 308 ft (94 m)[3] |
| Reservoir | |
| Creates | Hetch Hetchy Reservoir |
| Total capacity | 360,400 acre⋅ft (444,500,000 m3)[2] |
| Catchment area | 459 sq mi (1,190 km2)[2] |
| Surface area | 1,972 acres (798 ha)[2] |
| Power Station | |
| Turbines | 3 x Pelton turbines at Kirkwood Powerhouse 2 x Pelton turbines at Moccasin Powerhouse[4] |
| Installed capacity | 234 MW[4] |
| Annual generation | 976 GWh[5] |
O'Shaughnessy Dam is a 430-foot (131 m) high concrete arch-gravity dam in Tuolumne County, California, United States. It impounds the Tuolumne River, forming the Hetch Hetchy Reservoir at the lower end of Hetch Hetchy Valley in Yosemite National Park, about 160 miles (260 km) east of San Francisco.[6] The dam and reservoir are the source for the Hetch Hetchy Aqueduct, which provides water for over two million people in San Francisco and other municipalities of the west Bay Area. The dam is named for engineer Michael O'Shaughnessy, who oversaw its construction.[7]
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Although San Francisco had sought Tuolumne River water as early as the 1890s, this project did not move forward until the disastrous earthquake and fire of 1906, which underscored the insufficiency of the existing water supply. The Hetch Hetchy Valley – then compared to Yosemite Valley for its scenic beauty – was chosen for its water quality and hydroelectric potential, but the location within the national park generated controversy. An act of Congress was required to circumvent federal protection of the Tuolumne River, with the reasoning that public land should be developed for the public benefit.
Construction of the dam started in 1919 and was finished in 1923,[8] with the first water delivered in 1934 after numerous delays. From 1935 to 1938, the dam was raised to increase its capacity for water supply and power generation. The dam, aqueduct and appurtenant hydroelectric systems are collectively known as the Hetch Hetchy Project. Deriving from a largely wild and pristine area of the Sierra Nevada, the Hetch Hetchy supply is some of the cleanest municipal water in the US, requiring only primary filtration and disinfection.[9]
Hetch Hetchy represented the first great environmental controversy in the US,[10] and debate over the dam and reservoir continues today. Preservationist groups such as the Sierra Club lobby for the restoration of the valley, while others argue that leaving the dam in place would be the better economic and environmental decision.[11]
- ^ "O'Shaughnessy Dam". Geographic Names Information System. United States Geological Survey, United States Department of the Interior. 2000-06-14. Retrieved 2013-05-25.
- ^ a b c d e f "Dams Within the Jurisdiction of the State of California: Listed Alphabetically By Name of Dam" (PDF). Division of Safety of Dams. California Department of Water Resources. 2012. Retrieved 2013-05-25.
- ^ a b Bolin, Leslie K. (1987). "Hetch Hetchy: Facts and Figures" (PDF). U.C. Davis Environmental Law Society. University of California Davis. Retrieved 2013-05-25.[permanent dead link]
- ^ a b "Tuolumne River System" (PDF). Archived from the original (PDF) on 2014-07-02. Retrieved 2013-05-25.
- ^ "Chapter 9: Impact of restoration on hydropower production and revenues". Environmental Defense Fund.
- ^ USGS Topo Maps for United States (Map). Cartography by United States Geological Survey. ACME Mapper. Retrieved 2013-05-25.
- ^ "The O'Shaughnessy Dam Debate: Transcript". PBS NewsHour. PBS. 2005-08-12. Retrieved 2013-05-25.
- ^ "O'Shaughnessey Dam". Hetch Hetchy: Preservation or Public Utility?. In Time & Place. January 2011. Retrieved 2013-05-25.
- ^ Worth, Katie (2011-07-18). "Hetch Hetchy water goes through ultraviolet rinse". San Francisco Examiner. Archived from the original on 2011-11-01. Retrieved 2014-04-12.
- ^ "Hetch Hetchy Environmental Debates". The Center for Legislative Archives. National Archives. Retrieved 2014-04-12.
- ^ Rogers, Paul (2012-09-30). "Hetch Hetchy controversy: Could Yosemite's 'second valley' be restored?". San Jose Mercury News.
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