Yuba Water Agency has awarded a $76.8 million contract to upgrade key components of its hydropower generation infrastructure in the Yuba County foothills. A joint venture company made up of Obayashi and Drill Tech Drilling & Shoring, Inc. was awarded the contract for the agency’s Colgate tunnel outage project, set to begin in the fall of 2025.
The tunnel outage will focus on a four-mile-long rock tunnel and one-mile-long penstock pipe that carries water from New Bullards Bar Reservoir to New Colgate Powerhouse 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. The upgraded valve will enhance the agency’s ability to protect downstream infrastructure and improve maintenance access without requiring the entire tunnel to be dewatered.
“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,” said Yuba Water Hydro Engineer Casey Peterson, one of the lead engineers on the project.
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 specialized parts. For instance, the agency worked for more than one year to secure three 14-foot-diameter, 11-ton connectors, called flanges, which will be installed as part of the new protective valve.
Staging for the project is expected to begin in September 2025, with the bulk of the work planned for October through January 2026. Colgate’s hydropower generation units will be offline during the entirety of the outage.
Yuba Water is funding these critical capital improvements with revenue generated from its hydropower sales along with state grant funds.