Will a Landslide on the Eel River Cause California’s Next Dam Disaster?

An historic landslide looms above Scott Dam, owned by Pacific Gas & Electric Co. The utility is trying to sell off the dam without acknowledging the danger posed by this geologic threat and a nearby earthquake fault.

Written by Scott Greacen Published on Read time Approx. 5 minutes
Scott Dam, owned by Pacific Gas & Electric Co., on the Eel River in California. The landslide that may threaten the dam is just outside the photo on the right. Photo courtesy PG&E

Pacific Gas & Electric Co. (PG&E) wants to sell its two dams on California’s upper Eel River as soon as possible. Part of a diversion scheme called the Potter Valley Project, the utility wants to get the dams off its balance sheet so badly it is moving to auction them off right in the middle of a Federal Energy Regulatory Commission (FERC) relicensing process. Scott Dam will be 102 years old, and Cape Horn 112 years old, when their current federal license expires in 2022.

Wouldn’t it make sense to be sure the dams are actually safe before PG&E auctions them off, or before FERC grants a new 50-year license?

new study commissioned by my group, Friends of the Eel River, shows there are risks associated with the Eel River dams nobody has troubled to analyze before. In this case, a landslide hanging just above Scott Dam presents “a significant geological hazard” to the dam itself thanks to the earthquakes that are likely in this area. This assessment adds to the portfolio of threats from the nearby Bartlett Springs fault complex.

Mendocino County interests, which have long enjoyed diversion of Eel River flows into Potter Valley and the upper Russian River, don’t seem particularly concerned about the safety of Scott Dam. Through the obscure Mendocino County Inland Water and Power Commission, agricultural and urban interests such as the Potter Valley Irrigation District and the city of Ukiah are seeking a deal with PG&E to keep the dams in place. Others surely are as well.

Neither PG&E nor state and federal regulators have much incentive to uncover the Potter Valley Project’s huge liabilities. PG&E is still trying to sell the project, after all. And FERC sees its mission as promoting and protecting electrical generation – even the relatively tiny, and entirely uneconomic, amount of hydroelectric power produced at the PG&E powerhouse in Potter Valley.

For its part, FERC has flatly refused to discuss dam safety issues during relicensing of the Eel River dams. Nor will FERC address the need to consider dam decommissioning and removal. (FERC says it will analyze dam removal only if the dam owner asks for it. That PG&E has declined to request dam removal studies may have something to do with the fact that the company is trying to sell the dams, rather than get stuck with $100 million or more in federally mandated removal costs.)

Make no mistake, our primary interest at Friends of the Eel River is the recovery of Eel River fisheries, especially salmon and steelhead now listed under the federal Endangered Species Act. We are focused on the opportunity to restore Chinook and steelhead to hundreds of miles of prime spawning and rearing habitat on federal public lands by removing Scott Dam, which blocks fish passage completely. But the more we dig into questions of dam safety, the more cause for alarm we’ve found. It’s important to note that these safety issues undermine all the putative benefits of leaving the dams in place: A water supply that depends on a suspect dam next to a fault is anything but sustainable.

We asked Miller Pacific Engineering Group to address some key questions: Could a significant earthquake on the nearby Bartlett Springs fault cause the landslide above Scott Dam to fail? If it did fail, what might be the effects on the dam itself?

The answers are sobering. The landslide – which began moving before Scott Dam was built – is not stable. The larger an earthquake, the more likely the slide will be to move a lot. If the slide were to move substantially, it could put significant forces on the dam that could lead to dam failure.

For all its public assurances that Scott Dam may be just fine for another 50 years, PG&E has not been eager to share the dam safety information it does have. Much of this material is hidden from public view as so-called critical energy infrastructure information, on the basis it might be useful to terrorists. We’ve asked the company to consider releasing more of this information. It has not responded.

It is shocking to us that Scott Dam was built so close to a fault capable of producing very significant earthquakes. However, this is not uncommon. There are two reasons why many dams across the American West were built near faults.

The first is ignorance. When Scott Dam was built in 1920–21, the idea of continental drift had just been proposed as a scientific concept. The theory of plate tectonics was still three decades from winning scientific acceptance. Discovery of the Bartlett Springs fault was 50 years in the future.

The second reason is that where rivers cross faults, we find tight spots downstream of wide areas: seemingly perfect places for dams. As the two sides of a fault move relative to one another, the shifting sides pinch the river canyon, forming narrow places that are easier to dam. Meanwhile, upstream sections of riverbed are pushed away from the watercourse, creating wide valleys ideal to hold water. As many as 100 California dams may be at serious risk from faults. High-profile examples include Isabella Dam, on the Kern River above Bakersfield; Oroville Dam on the Feather River; and Martis Creek Dam, above Truckee. Calaveras Dam, near San Jose, has just been rebuilt to withstand a 7.25 magnitude quake, at a cost of $823 million.

As we noted, we have asked FERC to examine dam safety in relicensing the Eel River dams, to no avail. We’ve also asked FERC, in light of the recent disaster at Oroville Dam, to consider updating its inspection protocols for older and at-risk dams such as Scott Dam. Again, FERC has declined to respond.

Of the 1,246 dams under jurisdiction of the California Department of Water Resources’ Division of Safety of Dams (DSOD), only Oroville – now having its spillway rebuilt on an emergency basis – is rated “unsatisfactory.” DSOD rates Scott Dam as “satisfactory,” by which it means “no existing or potential dam safety deficiencies are recognized.” We have asked DSOD to explain how they will reevaluate this rating in view of Miller Pacific’s finding that the landslide above Scott dam poses “a significant geological hazard” to the dam.

PG&E is walking around in the scientific equivalent of the emperor’s new clothes. The utility is offering to sell a dam built less than a mile from what turns out to be the most active portion of a very substantial earthquake fault: The Bartlett Springs fault is the easternmost extension of the San Andreas fault system. And it hasn’t even taken a hard look at how a significant earthquake could affect the landslide perched pretty much right above Scott Dam.

It’s time to get real about risks and solutions. It’s time to negotiate a deal to remove Scott Dam.

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