Calaveras Dam Project reaches critical milestone with new spillway

Fremont, Calif. — The Chief of the California Department of Water Resources, Division of Safety of Dams (DSOD) joined officials from the San Francisco Public Utilities Commission (SFPUC), and the Bay Area Water Supply and Conservation Agency (BAWSCA) to announce the completion of the spillway at the Calaveras Dam Replacement Project. This major milestone brings the project a giant step closer toward completion and a more reliable water supply for 2.6 million customers in four Bay Area counties.

“We know that a major earthquake in the San Francisco Bay Area is only a matter of time, and that’s why we are making significant investments into our Hetch Hetchy Regional Water System,” said Mayor Ed Lee. “These investments will help increase our resiliency and help us withstand the effects of earthquakes, droughts and other disasters. We have also made significant investments in our people and our regional economies while strengthening our critical water infrastructure. The Calaveras Dam project has employed 900 workers earning nearly $50 million in wages and benefits, many of whom are from the Bay Area.”

Every dam project consists of several major components, including the dam foundation, the dam itself, the spillway, and the outlet works that allow water to be released from the reservoir for transmission to treatment facilities and eventual delivery to the customers.

“This spillway is a critical safety feature of the new Calaveras Dam,” said David Gutierrez, Chief of the California Division of Safety of Dams. “This massive concrete structure controls excess flows into the reservoir by releasing them safely through the spillway. The new dam cannot be completed without a spillway that is robust enough to protect the dam.”

Construction on the replacement Calaveras Dam began in 2011. Work on the concrete spillway began in March 2014 and took two years to complete.  The structure is 1,550 feet long, and 60 to 80 feet wide, with walls that vary from 20 to 40 feet high. It was constructed with more than 50,000 cubic yards of concrete.

The Calaveras Dam Replacement Project Construction team literally built a spillway, the width of an eight-lane freeway, and anchored it to the side of a hill,” said Harlan L. Kelly, Jr., General Manager of the San Francisco Public Utilities Commission. “Tens of thousands of hours of work went into its construction. With the spillway complete, we will now continue to focus on the remaining major components of the project. The dam foundation and outlet works should be complete this late summer, and construction of the earth and rock fill dam will begin later this year.”

The original Calaveras Dam was completed in 1925 and impounds Calaveras Reservoir, which is the largest Bay Area reservoir in the Hetch Hetchy Regional Water System.  The reservoir has been kept at a lower capacity since 2001 due to seismic safety concerns about the existing dam. The active Calaveras fault is located approximately 1,500 feet from the existing dam. The future dam, along with its spillway and outlet works, will be designed to withstand a 7.25 magnitude Maximum Credible Earthquake on the Calaveras Fault.

“We live in earthquake country, and ensuring a reliable supply of drinking water after an earthquake is always foremost on the minds of Bay Area water providers, particularly at the anniversary of the 1906 earthquake,” said Nicole Sandkulla, CEO and General Manager for the Bay Area Water Supply and Conservation Agency. “Calaveras Reservoir, when full, represents more than half of all water storage of the Hetch Hetchy Regional Water System in the Bay Area. That storage is crucial to a reliable local water supply for 2.6 million people after an earthquake."

Construction to build a new earth and rock-fill dam downstream of the existing Calaveras Dam began in 2011 by the joint venture of Dragados USA, Flatiron Construction and Sukut Construction. Construction of the $810 million project is expected to be complete in mid-2019.  The project has encountered a number of construction challenges due to extremely difficult geologic conditions, which has led to increased costs and schedule impacts.  The project team has worked to minimize the impacts as much as possible.

The Calaveras Dam Replacement Project is the largest project of the $4.8 billion Water System Improvement Program (WSIP) to repair, replace, and seismically upgrade key components of the Hetch Hetchy Regional Water System.  The San Francisco Public Utilities Commission, together with our 26 wholesale customers, launched the WSIP in 2002. The WSIP is more than 90% complete, and it is one of the largest water infrastructure projects in the country.