Contractors use a crane and barge system to move and install a fixed cone valve, part of California Department of Water Resources’ refurbished River Valve Outlet System at Oroville Dam in Butte County, California. Photo courtesy of Sara Nevis, California Department of Water Resources

OROVILLE, CA (MPG) - The California Department of Water Resources has completed a $235 million rehabilitation of Oroville Dam’s river valve outlet system, an infrastructure project designed to improve the dam’s reliability and preserve access to cold water stored deep in Lake Oroville.

The river valve outlet system, known as the RVOS, allows DWR to release cold water from the lower portions of Lake Oroville into the Feather River. The system plays an important role during periods of extreme heat and drought, when colder water releases can help control downstream temperatures for fish populations.

Construction began in October 2022 and required crews to work deep inside one of the dam’s original diversion tunnels.

Contractors install rock anchors into native rock foundation material in preparation for construction of a concrete thrust block. Work is part of a project to refurbish California Department of Water Resources’ River Valve Outlet System at Oroville Dam in Butte County, California. Photo courtesy of  Xavier Mascareñas, California Department of Water Resources

“This investment in Oroville Dam’s infrastructure ensures the reliable and safe operation of the State Water Project’s largest flood protection and water supply facility,” said John Yarbrough, deputy director of DWR’s State Water Project. “DWR will continue to prioritize modernization projects to improve aging infrastructure in an ever-changing climate.”

Oroville Dam stands 770 feet tall and serves as a major component of the State Water Project. Built between 1961 and 1967, the earthen dam provides flood protection, water storage, hydroelectric power generation and recreation while supporting habitat in the Feather River.

The ability to draw colder water from deeper portions of Lake Oroville becomes especially important when reservoir levels fall during prolonged dry conditions, according to DWR.

Cold-water releases help maintain downstream temperatures for Chinook salmon and steelhead trout in the Feather River and support operations at the Feather River Fish Hatchery. DWR monitors river temperatures as part of its environmental requirements.

“Part of DWR’s mission is to operate State Water Project facilities to protect, restore and enhance the natural environment,” Yarbrough said. “This includes operating the Oroville-Thermalito Complex facilities in a way that supports Central Valley fish populations including Chinook salmon and steelhead trout, which spawn each year in the Feather River below the dam.”

A large valve is transported on a barge past the base of Oroville Dam's main spillway. The valve is part of a project to refurbish California Department of Water Resources’ River Valve Outlet System in Butte County, California. Photo courtesy of Andrew Nixon, California Department of Water Resources

DWR Principal Engineer and Project Manager Jason Brabec said the location and operating requirements complicated the rehabilitation work.

“Rehabilitating the RVOS was highly complex,” Brabec said. “It required immense coordination with contractors in a small space, all while ensuring that Hyatt Powerplant met its green energy commitments and cold-water release requirements.”

Crews used barges to transport valves, construction materials and equipment during the project. Workers also installed temporary bulkheads that allowed crews to work on portions of the valve system.

“Because this system is critical to Oroville Dam’s operations, all phases of the work required high construction standards and safety protocols,” Brabec said.

Syblon Reid of Folsom and The Dutra Group of San Rafael formed a joint venture to complete the rehabilitation project.

DWR completed commissioning of the valve system in June.

The department said the rehabilitation forms part of its continuing work to modernize Oroville Dam and other State Water Project facilities as infrastructure ages and California faces periods of extreme heat and drought.