Hetch Hetchy Water System Improvements

The Hetch Hetchy Water System provides approximately 260 million gallons of water per day to 2.4 million people in the California counties of San Francisco, Santa Clara, Alameda, and San Mateo. The Sierra Nevada snowmelt, stored within a reservoir in Yosemite National Park, supplies 85 percent of this water. It then flows 160 miles by gravity through a series of tunnels and pipelines to the Bay Area. This water/hydropower system delivers an average of 1.7 billion kilowatt hours of electricity annually to the City and County of San Francisco, the Modesto and Turlock Irrigation Districts, and tenants at the San Francisco International Airport.

Heightened awareness following the 1989 Loma Prieta earthquake and drought conditions in the 1990s led the San Francisco Public Utilities Commission to undertake an upgrade and rehabilitation program for the entire water system. Jacobs Associates has provided tunnel engineering services on several hydropower projects within the Hetch Hetchy Water System, including:

• Moccasin Penstock Replacement Project: Conceptual design services for the evaluation of a penstock tunnel 3,450 feet (1,051 m) long, 13 feet (4 m) in diameter, with an internal 10-foot-diameter (305 cm), welded steel pipeline for the Moccasin Power Plant. .
• Canyon Power Tunnel Inspection and Adit Repair: Inspection services on a 10.3-mile-long (16.5 km) horseshoe-shaped tunnel 14.5 feet high (4.4 m) by 14 feet wide (4.27 m) that connects the O’Shaughnessy Dam/Hetch Hetchy Reservoir with the Kirkwood Powerhouse.
• Mountain Tunnel Condition Assessment—Lifecycle Analysis and Rehabilitation: Inspection services for a tunnel 99,655 feet long (30,375 m) that carries water from the Early Intake Reservoir (Kirkwood Powerhouse) to Priest Reservoir.
• South Fork East Repairs: Assisting in the repair of the Mountain Tunnel at the South Fork of the Tuolumne River.