Flatiron Dragados Sukut JV receives $1.88-billion contract
Construction is set to begin on one of the nation’s largest dam safety projects as the approximately $2.8-billion Anderson Dam Seismic Retrofit Project advances from years of engineering, environmental review and federal permitting into a seven-year reconstruction program.
The Santa Clara Valley Water District Board of Directors announced the $1.88-billion construction contract July 28 to the Flatiron Dragados Sukut ADSRP joint venture, spokesman Matt Keller confirmed to ENR.
Reconstruction includes replacing the aging hydraulic infrastructure of the 235-ft-high earthfill dam and restoring Santa Clara County’s largest reservoir to full operating capacity after nearly six years of storage restrictions due to seismic safety concerns.
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“This milestone reflects years of hard work, collaboration, and perseverance by our staff, contractors, regulators, and community partners,” Valley Water Board Chair Tony Estremera said following the award.
Rebuilding Instead of Retrofitting
Rather than retrofit the existing structure, the project calls for removing and rebuilding most of Anderson Dam to meet modern federal dam safety requirements.
Major work includes a new downstream embankment buttress, replacement of the outlet works with high- and low-level outlets, a new spillway, and extensive foundation treatment and seepage controls. Permanent instrumentation will monitor long-term performance, and the project also calls for decommissioning the dam’s 800-kW hydroelectric facility.
The Federal Energy Regulatory Commission approved the reconstruction plan in June after concluding it addressed the dam’s identified seismic deficiencies and met federal dam safety requirements.
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The Anderson Dam Seismic Retrofit Project begins with a partially dewatered reservoir and the existing embankment, and concludes with a reconstructed dam designed to meet modern seismic standards following phased construction. Click to enlarge.
Graphic courtesy of Valley Water
State Water Board permitting documents note the reconstructed facility is designed to withstand maximum credible earthquakes on the Calaveras and Coyote Creek faults, safely pass the probable maximum flood and provide outlet capacity capable of rapidly lowering the reservoir during an emergency.
The Anderson project is one of several major California dam safety investments, including the ongoing seismic modification of B.F. Sisk Dam, another large earthfill embankment undergoing extensive upgrades to improve earthquake performance.
Valley Water lowered Anderson Reservoir by approximately 50 ft in 2020 after FERC determined that portions of the embankment could sustain significant damage during a major earthquake due to liquefaction risks in the foundation and dam materials. The storage restriction substantially reduced water supply capacity while engineers developed a permanent reconstruction strategy.
Construction Sequence
Permit documents outline a minimum seven-year construction sequence beginning with reservoir dewatering, staged excavation of the existing embankment and work on new outlet facilities. The more than 1,000-ft-long Anderson Dam Tunnel Project—one of the key precursor projects for the reconstruction—is now in its final stages.
Crews remove the tunnel boring machine after it completed the Anderson Dam Tunnel Project’s lake tap, creating the underwater connection between the new outlet tunnel and Anderson Reservoir. The tunnel will allow controlled reservoir releases while the dam is reconstructed over the next seven years.
Photo/Valley Water
Ryan McCarter, Valley Water deputy operating officer for the Dam Safety & Capital Delivery Division, says the tunnel’s reinforced-concrete lining uses articulated joints that “can move actually a few feet without the tunnel collapsing” if seismic ground movement occurs. The tunnel diameter is 24 ft.
Keller, the utility’s spokesman, says the tunnel project will be completed before reconstruction begins in early 2027. Once operational, it will allow crews to maintain the reservoir at a controlled level while the existing dam is rebuilt.
The staged construction plan calls for portions of the existing embankment to be excavated and replaced over successive dry seasons, while temporary configurations continue to control reservoir releases.
Permanent work includes construction of the replacement dam in successive lifts, completion of the spillway and low-level outlet works, installation of a new intake tower and eventual refilling of the reservoir after approval from dam safety regulators.
Temporary works include cofferdams, diversion facilities to route Coyote Creek around the work area, haul roads and other supporting infrastructure. Contractors must maintain downstream flood protection while meeting extensive water quality, fisheries and habitat protection requirements throughout construction.
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Valley Water selected GEI Consultants to provide construction management services for the seven-year reconstruction. The firm’s responsibilities include resident engineering, construction inspection, quality assurance, environmental compliance and coordination among contractors, designers and regulatory agencies throughout construction.
The construction contract concludes a procurement that used California’s legislatively authorized Best Value selection process, allowing Valley Water to evaluate technical qualifications, project approach and price for one of the state’s most technically complex public works projects.
