Yuba County-based public entity Yuba Water Agency has awarded a $76.8m contract to upgrade key components of its hydropower generation infrastructure in the Yuba County foothills.
The contract was given to a joint venture of Obayashi and Drill Tech Drilling & Shoring. The project focuses on the Colgate tunnel outage and is scheduled to begin in fall 2025.
The tunnel outage will target a four-mile-long rock tunnel and a one-mile-long penstock pipe.
These components carry water from New Bullards Bar Reservoir to New Colgate Powerhouse, located at the base of Lake Francis Road in Dobbins.
During the outage, Yuba Water will remove rocks and debris, repair and reinforce worn parts, and install a new protective valve system at the top of the penstock pipe.
According to Yuba Water Agency, the upgraded valve will improve downstream infrastructure protection and allow easier maintenance without needing to dewater the entire tunnel.
Yuba Water hydro engineer Casey Peterson said: “Even though recent inspections show the tunnel is in good condition, this project will reinforce key areas to help prevent future unplanned outages and ensure reliable operations for decades to come.”
Yuba Water has been planning for the tunnel outage since 2017, conducting remote inspections of the tunnel system and working with contractors and manufacturers to design and fabricate specialised parts.
The public agency worked for more than one year to secure three 14ft diameter, 11 tonnes connectors, called flanges, which will be installed as part of the new protective valve.
Staging for the project is set to begin in September 2025, with major work scheduled from October to January 2026. During this period, Colgate’s hydropower generation units will be offline.
Yuba Water is funding these essential improvements through hydropower revenue and state grant funds.
In December last year, Yuba Water committed over $2.9m to improve water delivery reliability for Yuba County farmers by lining several miles of canals in the Hallwood Irrigation Company’s service area.
