A Feat of Gravity

A Feat of Gravity. The Hetch Hetchy Regional Water System. After the 1906 earthquake and its resulting fires destroyed much of San Francisco, public support surged for a reliable water supply. This allowed San Francisco to look beyond the Bay Area to resolve the region’s growing need for reliable, high-quality water. The 1913 Congressional Raker Act authorized San Francisco to use the Tuolumne River in Yosemite National Park’s Hetch Hetchy Valley as a municipal water supply., Today, spring snowmelt from the Tuolumne River fills Hetch Hetchy Reservoir, the largest reservoir in the SFPUC water system. Gravity then moves the water to over 2.7 million people. More than half flows to customers in Alameda, Santa Clara, and San Mateo Counties, while the rest is either delivered to San Francisco or stored in local reservoirs such as Lower Crystal Springs. , Inset Caption , You are standing near the Lower Crystal Springs Dam on San Mateo Creek. This dam was constructed in 1888 using interlocking concrete blocks. Although located adjacent to the San Andreas Fault, the dam survived both the 1906 and 1989 earthquakes without any significant damage.