Hetch Hetchy Aqueduct, Water aqueduct in California, United States.
The Hetch Hetchy Aqueduct is a water supply system in California that carries drinking water from the Sierra Nevada mountains to the San Francisco Bay Area through a mix of tunnels and open pipelines. The route crosses very different kinds of terrain, from high mountain slopes down to low coastal plains.
After the 1906 San Francisco earthquake exposed the city's fragile water supply, Congress authorized construction of the system in 1913 on federally protected land, a decision that drew strong opposition from conservationist John Muir. The aqueduct began delivering water in 1934, after years of tunneling and pipeline work.
The name Hetch Hetchy comes from a word used by the Indigenous Miwok people, believed to refer to a type of grass that once grew in the valley now flooded by the reservoir. That valley, before it was dammed, looked much like Yosemite and drew visitors from across California.
Some sections, including the O'Shaughnessy Dam at the start of the system, are open to visitors, while other parts of the route are not publicly accessible for safety reasons. Checking access conditions before visiting is a good idea, especially for areas within the Yosemite region.
The system passes directly through one of the most seismically active zones in California, and engineers had to design the tunnels and pipes to flex rather than break during ground movement. This was a major technical challenge at a time when earthquake engineering was still a very young field.
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