The Colgate Tunnel and Penstock Improvement Project focuses on maintenance to the five-mile-long tunnel and one-mile-long penstock pipe that move water from New Bullards Bar Reservoir to New Colgate Powerhouse to generate hydropower. This is major maintenance that happens very infrequently but is needed to ensure the longevity of the tunnel and Yuba Water’s hydropower operations.

During the project, the flow of water is shut off between New Bullards Bar Dam and New Colgate Powerhouse to allow crews to safely access the inside of the tunnel to remove debris, repair and reinforce worn areas and to install a new protective valve at the top of the penstock pipe. While this work is being done, Yuba Water will also be doing several other large capital improvement projects in its powerhouse.

Flows in the North Yuba River will be maintained, as Yuba Water will make releases through another outlet at New Bullards Bar Dam.

The project will improve the reliability of Yuba Water’s hydropower operations by upgrading a critical protective valve system, reinforcing parts of the tunnel and removing debris like rocks and sediment to prevent future unplanned outages and improving access for maintenance in the future. All of the work for the project is considered critical.

Pre-construction staging will begin in September 2025. The main work will take place from October 2025 through mid-February 2026.

The contract awarded for this project is $76.8 million. Because we will not be able to generate at our New Colgate Powerhouse during the work, we will also lose revenue during the outage. Yuba Water is also dedicating significant staff time and resources to this project.

Yuba Water is paying for the project with revenue generated from our hydropower along with some state grant funding. Yuba Water is a wholesale power and water provider; we do not provide residential water or power or earn income from ratepayers or taxpayers.

Yuba Water is working with a joint venture company made up of Obayashi and Drill Tech Drilling & Shoring, Inc. to complete the work. Additional professionals who have worked on similar projects will also be involved, including Delve Underground, TCB Industrial Contractor, Bay-Area Coating Consultants and others. Yuba Water's own staff will also be heavily involved and on-site throughout the outage.

These upgrades will improve the overall reliability of our operations, reduce the risk of unplanned outages and ensure we can continue providing clean, carbon-free hydropower – and revenue to reinvest back into Yuba County communities – for decades to come.

Starting in spring 2025 through the fall, Lake Francis Road residents may notice a slight increase in traffic and activity in the area. This includes oversized trucks (about one truck a week) transporting equipment and large, heavy pieces of pipe that will be used during the outage.

Construction staging areas will be set up starting in early September. The actual outage will begin October 1 through late February 2026. During this time, residents can expect additional traffic in the area. Although some work will take place at night, Yuba Water is committed to minimizing the impacts from construction as much as possible.

Residents are encouraged to subscribe to our alerts for this project to be informed of specific impacts on specific days that will be firmed up as we get closer to construction.

Due to the relative depths of domestic wells in the area and the disconnected nature of groundwater in the foothills, Yuba Water does not anticipate significant impacts to groundwater in the area while the tunnel is dry. If that changes, Yuba Water will work directly with individual property owners to reduce any potential impacts.

Additionally, we are not completely sealing the rock tunnel, which means and modest contributions to local groundwater through seepage will continue following the outage.

Yuba Water will maintain flows in the North Yuba River by making releases through another outlet at New Bullards Bar Dam.

Check out engage.yubawater.org for the latest project information and updates.

We welcome your questions and discussion on our project website. For construction-specific questions or concerns during the project, please contact Kush Chohan with Delve Underground. You can also email us with general questions or feedback at communications@yubawater.org or call (530) 741-5000.