California’s largest dam rebuild moves from planning to construction
Subscribe to our free newsletter today to keep up to date with the latest construction news.
California has taken a significant step toward restoring one of its most important water infrastructure assets after Valley Water awarded a $1.88 billion construction contract to the FlatironDragados-Sukut joint venture. The award moves the Anderson Dam Seismic Retrofit Project from planning into delivery and ranks among the largest civil engineering contracts awarded in the US water sector this year.
Construction is expected to begin in 2027 after preparatory work and permitting are complete. The overall program is now estimated at approximately $2.8 billion, reflecting years of engineering, environmental review and enabling works.
The project goes well beyond a conventional retrofit. Much of the existing embankment will be reconstructed while new outlet works and an expanded spillway will be built to meet modern seismic and flood safety standards.
For California’s construction industry, the contract reflects continued investment in major water infrastructure. For Silicon Valley, it marks progress toward restoring a reservoir that has operated under severe restrictions for several years.
The project requires reconstruction rather than conventional strengthening
Completed in 1950, Anderson Dam is Valley Water’s largest reservoir and one of the most important components of Santa Clara County’s water system. Engineering studies concluded that the structure would not adequately withstand a major earthquake, leading federal regulators to require a substantial reduction in reservoir levels until permanent improvements could be completed.
The reservoir currently operates at roughly 3% of its designed capacity, sharply limiting its ability to store water, replenish groundwater and support regional water management.
The construction program will rebuild large sections of the embankment instead of carrying out isolated repairs. The scope includes new outlet facilities capable of safely releasing water during emergencies, an extended and modernized spillway and foundation improvements throughout the structure.
The completed works are intended to meet current seismic performance standards while improving flood management and operational resilience for decades.
Construction sequencing will be critical. Supporting tunnel works and outlet improvements must be completed before the main reconstruction begins, reducing construction risk once large-scale earthworks are underway.
Restoring the reservoir strengthens long-term water security
The project carries strategic importance well beyond engineering.
Anderson Reservoir holds approximately 90,000 acre-feet of water and is the largest storage facility in Valley Water’s system. It supports drinking water supplies, groundwater recharge, environmental flows and downstream flood management. Valley Water estimates the reservoir can store enough water to supply nearly one million people for one year under normal operating conditions.
Restoring that storage capacity will improve drought resilience, reduce dependence on imported water supplies and provide greater flexibility as California adapts to more variable weather patterns.
The contract also reflects growing demand for contractors with specialist experience in complex water infrastructure. FlatironDragados and Sukut previously worked together on the Isabella Dam Safety Modification Project, providing experience in major earthworks, hydraulic structures and highly regulated construction environments.
The seven-year construction program will require careful coordination among the owner, contractor and regulators while managing environmental commitments, seasonal weather and cost control across a multibillion-dollar project.
The award marks the transition from years of planning to construction. If delivered on schedule, the rebuilt Anderson Dam will restore critical water storage capacity, improve seismic resilience and strengthen long-term water security across Silicon Valley.
Source
