Issue link: https://geospatial.trimble.com/en/resources/i/1479770
/ Working deep beneath San Francisco Bay, Party Chief Russ Mello prepares to collect survey data. Precision measurements and analysis produce millimeter accuracy for guiding the tunnel boring machine. January 7, 2013 John Stenmark LS Tunnel Beneath the Bay For decades, California's Hetch Hetchy water system has supplied water to the San Francisco Bay Area. But the aging system is nearing the end of its useful life and is seismically vulnerable. Constructing a solution requires accurate, nerve-racking surveying. Stretching from the Sierra Nevada Mountains across central California to the San Francisco Bay, the Hetch Hetchy water system is one of the largest water collection systems in the U.S. The system collects water from the Tuolomne River watershed in the Sierra Nevada and stores it in three reservoirs in Yosemite National Park. From there, a series of tunnels and pipelines carry the water 150 miles west to consumers in the Central Valley and in the San Francisco region. Handling more than 220 million gallons of water every day, the system serves more than 2.4 million residents and businesses. In addition to supplying 85 percent of San Francisco's water demand, the Hetch Hetchy system generates roughly 1.7 billion kilowatt-hours of electric power every year. But Hetch Hetchy is showing its age. Many of its reservoirs, aqueducts and support facilities are 75 to 100 years old. Because of the deteriorating facilities, maintenance costs are signicant drains on the system's nancial resources. And, in addition to the normal aging and wear, the system is susceptible to damage from potential earthquakes in the seismically active region. Many structures do not meet modern building codes for seismic protection, and a major earthquake could disrupt Bay Area water service for weeks or longer. To reduce the risk, the San Francisco Public Utilities Commission (SFPUC) embarked on a multibillion dollar project in 2002 to upgrade and modernize the Hetch Hetchy water system. Known as the Water System Improvement Program (WSIP), the effort is the largest infrastructure program ever undertaken by This website requires certain cookies to work and uses other cookies to help you have the best experience. By visiting this website, certain cookies have already been set, which you may delete and block. By closing this message or continuing to use our site, you agree to the use of cookies. Visit our updated privacy and cookie policy to learn more.