Hetch Hetchy is the name of a valley, a reservoir, and a water system. The valley lies in the northwestern part of Yosemite National Park. Connecting Hetch Hetchy to coastal California is a 175 mile system that brings San Francisco and nearby municipalities their primary source of water and power. John Muir, a naturalist and conservationist, with the support of the Sierra Club fought a gallant, yet losing battle to protect Hetch Hetchy Valley from ruination by the city of San Francisco.
After the 1906 earthquake San Francisco was desperate for a reliable source of water and power. In 1913 Congress passed an act authorizing construction of a dam. The O'Shaughnessy Dam, named after the engineer who oversaw its construction, was completed in 1923. Between 1935 and 1938 the dam was raised 85 ft to increase its capacity. Included in the construction was a 500 ft tunnel, cut through solid granite. One must go over the dam and through the tunnel to reach the popular trail that leads to Wampa Falls. I can testify that the tunnel is dark and wet; the few lights accomplish little. Basically, the tunnel is very dark and very wet, as the roof and walls drip continually. The photo is not the best quality, but it does illustrate this fascinating tunnel. The only way to avoid the pools of water is to walk close to the wall and hope for the best.
Have no fear there is light at the end of the tunnel.
The Tuolumne River which is a primary source of the water for the reservoir, flows down Wampa Falls. (photo, center left) I did attempt the walk to Wampa, but due to a change in weather and the time of day, as I still had a four plus hour drive over the death defying Hwy 49 to my night's lodging (I am not exaggerating); I turned around.
The reservoir is eight miles long; when full it has a capacity of 360,400 acre ft. An acre foot is equivalent to 325,851 gallons. Down stream, the three associated power plants produce 1.6 billion kilowatt hrs a year. Now, be sure you are sitting down when you read this - To use the Hetch Hetchy Valley as a reservoir, San Francisco pays an annual fee, set by law in 1913, of $30,000. (A one bedroom apartment is San Francisco goes for $2,500 a month or $30,000 a year.)
The Sierra Club continues to support the restoration of the Valley. Sierra Club founder John Muir called Hetch Hetch Valley,"a grand landscape garden, one of Nature's rarest and most precious mountain temples."
Map of the Hetch Hetchy project is from Wikipedia.