San Francisco Water Quality: Yesterday
When early settlers came to the Bay Area, they discovered a plethora of artesian aquifers, but these were depleted after the Gold Rush. As San Francisco grew, its residents and businesses dumped domestic and industrial waste into the local city creeks and streams forcing the city to import water from outside the city.
In 1860, the newly-chartered Spring Valley Water Company dug wells in the farm districts of East Bay, damned a coastal stream to fill a wooded watershed, and then built a 32-mile flume to deliver water north to San Francisco. However, this above-ground aqueduct system was destroyed during the Great 1906 Earthquake, which destroyed 80% of the city’s structures.
The city engineers charged with rebuilding San Francisco needed to find a more secure way to provide water. City planners wanted to dam the Tuolumne River in the Hetch Hetchy Valley in the northwestern part of the Yosemite National Park. After a decade long battle with the Federal government and an act of Congress, the city of San Francisco gained permission to build the O’Shaughnessy Dam. Upon completion of the dam in 1923, the Hetch Hetchy valley was flooded. The dam and gravity-fed system began delivering virgin snowmelt from the Sierra Mountains to residents of San Francisco 148 miles away.