A Closeup View of the New Colgate Penstock Failure

A Lookout Superfan flew their drone over the failed penstock, in Yuba County, yesterday, and sent us the imagery. It shows the actual failure in clear detail, and also draws a good picture of the larger-scale impacts that the spillage of millions of gallons of water had on the slope below. We did a Lookout Livestream about the imagery, today, which is viewable here, and also embedded below the following photos.

View of first area impacted by floodwaters

Broken pipe section in first 100 yards of penstock

Broken pipe section and undermined footings

Undermined footings and wreckage below rupture site

The damage to the penstock is very extensive. Water flowed directly under the pipeline for much of its length, undermining many of the massive concrete footings which hold up the pipe, with ranges from 14.5 feet at the top down to 9′ at the terminus. Repairing the damage will cost hundreds of millions of dollars, and take a very long time. Much of our discussion in the livestream video looks at potential long-term regional impacts of having this piece of critical infrastructure be out of commission. This pipeline was the primary way that the Yuba County Water Agency delivered water from New Bullards Bar Reservoir to downstream water users (agricultural, urban, and environmental users). Without it, the YWCA has only the spillway gates at New Bullards Bar Dam and a relatively small outlet (1/3 the volume of the New Colgate tunnel and penstock) to release water from the dam.

There are also impacts to the regional power grid. The twin turbines at the New Colgate Hydropower Plan were operated with an extremely flexible approach, and provided grid operators the ability to quickly ramp up or down power generation as needed to meet peaks in electricity demand. We don’t yet have much information on the potential impacts on grid operations this summer, but managers have lost some flexibility that this project provided.

Lookout Livestream

Summary (AI-generated, reviewed by The Lookout).

In this livestream, Zeke Lunder explains the recent penstock failure at the New Colgate Powerhouse in Yuba County, using new drone footage to illustrate the damage and its implications for water management, fisheries, and the finances of the Yuba County Water Agency.

The powerhouse sits on the North Yuba River in the northern Sierra Nevada Mountains. A roughly half‑mile‑long penstock (about 14 feet in diameter at the top, narrowing to 9 feet) ruptured where the 4 mile-long tunnel exits the mountain and becomes pipe, releasing millions of gallons of water. This caused massive erosion and gullying, severely undermining the concrete footings and cracking or breaking several sections of the pipe, as well as washing out the main access road.

Although the powerhouse is mostly underground and appears less damaged inside than first feared, the surrounding site—including a PG&E switchyard where multiple transmission lines converge—suffered extensive damage from debris and flood flows. Much of the debris and erosion buried portions of the powerhouse area, and key access roads have been deeply incised and rendered impassable.

Because the powerhouse outlet cannot be used, reservoir releases now depend on the spillway and a small low‑flow outlet. The spillway works only while the lake is above its crest; once the lake falls below that level, operators must rely on a six‑foot‑diameter outlet that, while designed for 3,600 CFS, can safely pass only about 1,200 cubic feet per second (CFS)—far below the roughly 3,500 CFS the main powerhouse used to handle. This significantly reduces flexibility for both the YWCA to quickly release water from the dam if needed for flood management ahead of a major series of storms, and water their ability to deliver water to downstream user in the summer months.

The incident has major implications for agricultural and environmental water users. Rice growers and other irrigators in Yuba County, along with instream flow needs for fisheries on the lower Yuba River, depend on water stored behind Bullards Bar and routed through Englebright and diversion dams. With only 1,200 CFS capacity at the bottom outlet (about 2,500 acre‑feet per day), meeting typical annual allocations for agriculture and fish flows could quickly use up most of the system’s practical delivery capacity.

The powerhouse is also a critical, fast‑ramping resource on the regional power grid, with two large generators that could go from idle to full output in about 15 minutes. Losing this plant reduces the grid’s ability to respond quickly to peak electricity demand, shifting more strain to other, less flexible power sources.

Lunder notes that the Yuba County Water Agency is unusually large and sophisticated for a county‑run entity, operating a 600‑foot‑tall dam and major powerhouse, and that the financial hit could be enormous, potentially on the order of a billion dollars in repair costs plus lost revenue from power and water sales. The agency’s public communication and transparency have been relatively strong, which has helped maintain public goodwill.

The discussion also places the incident in a broader historical and environmental context: the region’s legacy of gold‑rush‑era waterworks (such as old hand‑dug ditches and hydropower origins) and concerns about oil spills from barrels swept into the river. Early tests have not detected PCBs, which were commonly used as cooling oils in large power transformers in the past, have which sometimes been stored in barrels for years at power plants after being phased out in the late 1970s. The situation underscores the age and fragility of California’s water infrastructure. For now, reservoir levels and spillway capacity appear adequate for near‑term flood control, but if a series of large storms or rain‑on‑snow events arrives, the loss of high‑capacity outlet and powerhouse operations could limit how aggressively operators can draw down the lake.