Sonoma, Mendocino county water managers propose pathway for continued Eel River diversions

Water managers in Sonoma and Mendocino counties seek to preserve water transfer infrastructure as part of PG&E license surrender for Potter Valley power plant.|

Water managers in Sonoma and Mendocino counties have submitted a conceptual proposal to PG&E to buy and maintain portions of the utility’s defunct Potter Valley power plant to enable future water transfers.

The move would be a critical step toward preserving seasonal diversions of Eel River water to supplement supplies in Lake Mendocino and the Russian River.

Working with the Mendocino County Inland Water and Power Commission and the Round Valley Indian Tribes, the Sonoma County Water Agency is seeking to preserve elements of the power plant through which water is channeled from the Eel River to the East Fork Russian River. No electricity would be generated as a part of the plan.

Potter Valley Powerhouse map
Potter Valley Powerhouse map

Pacific Gas & Electric has planned to surrender its license for the 1908 plant with the intent of decommissioning it. Without a proposal to save it, the diversion infrastructure would eventually be removed, leaving upper Russian River communities and agriculture users without sufficient water.

Studies using 110 years of hydrologic data show Lake Mendocino would go dry in roughly two of every 10 years without continued Eel River contributions, Assistant Sonoma Water General Manager Mike Thompson said. In eight out of 10, the reservoir would be unable to satisfy demands on it.

There has long been tension over the diversion of Eel River water, given declining fish stocks and existing water needs in Humboldt County. Fishery interests say Scott Dam, which impounds Lake Pillsbury, is a particular impediment to fish recovery, preventing access to what the California Trout conservation organization calls “prime habitat in the headwaters of the Eel.”

A coalition of fisheries groups — Friends of the Eel River, Pacific coast Federation of Fishermen’s Associations, the Institute for Fisheries Resources, California Trout, and Trout Unlimited — has a federal lawsuit pending against PG&E, saying its operation of the project and the dams violate the Endangered Species Act.

And they greeted Monday’s announced proposal skeptically.

Fisheries groups, said Alicia Hamann, executive director of the Friends of the Eel River, were excluded from the proposal’s development. But “more importantly, the needs of the Eel River fish were excluded,” in that they still bear the burden of diversions if something goes wrong, she said.

“It’s good to see these parties put forward a proposal, but it remains to be seen how much it actually changes anything,” said Matt Clifford, California Director of Law and Policy for Trout Unlimited. “The high-level goals — ensuring unobstructed fish passage past the former dam sites while allowing for continued water diversion at levels consistent with fish recovery on the Eel — are things we have supported for years.

“The hard part has always been coming to agreement on the specifics — how much water will be diverted, and when, and using what infrastructure, and who pays for it. This proposal punts resolution of those issues to the future.”

Scott Dam also has been deemed to be at greater seismic risk than previously believed, so PG&E has opened the gates to the dam permanently, preventing the lake from holding as much water as it used to. The utility said the dam eventually will come down as the plant is decommissioned.

Sonoma Water officials say the new proposal would still allow for removal of Scott and Cape Horn dams, leaving only the infrastructure necessary to funnel river water through the mile-long tunnel that leads to the East Fork Russian River.

Additional infrastructure would be added to improve fish passage and aid restoration of salmon and steelhead trout populations in the Eel River, as sought by tribes and conservation groups, while still channeling water into the diversion tunnel, Sonoma Water officials said.

“Our goals are to restore the Eel River watershed from its degraded condition and to restore our salmon fishery to sustainable and harvestable populations,” Round Valley Indian Tribes Tribal Council President Bill Whipple said in a news release. “We join this proposal because it is one pathway to achieving these goals.”

The diversion of Eel River water through what’s being called the New Eel-Russian Facility also would occur only during wet months, when flows are sufficiently high to support salmon and steelhead trout in the Eel while still contributing to Russian River water supplies on which thousands of consumers depend.

“We are going to dramatically reduce the window in which water can be diverted off the Eel River to times it’s very available and won’t do harm,” Sonoma Water General Manager Grant Davis said. “We really want to see both river basins come out better as a result of this solution.”

But conservation efforts over the last decade show consumers can get by with less water, officials said.

Sonoma Water, for instance, provided its contractors with 66,000 acre-feet of water in 2004. Last year, it sold 36,000 acre-feet, Thompson said.

Proponents of the new plan include the county of Mendocino, the city of Ukiah, the Redwood Valley County Water District, the Potter Valley Irrigation District and the Mendocino County Flood Control and Water Conservation Improvement District — all members of the Mendocino County Inland Water and Power Commission.

Commission Chairwoman Janet Pauli said those dependent on Lake Mendocino water — and who will bear the brunt of financing the project — have become increasingly aware of their reliance on contributions from the Eel River in recent years, owing in large part to the uncertainty created by Pacific Gas & Electric’s deliberations over re-licensing the power plant, which is more than a century old.

Sonoma and Mendocino County water providers, as well as stakeholders from Humboldt County and California Trout, initially had hoped to acquire the power plant license to ensure diversions continued.

Continued conversations resulted in the recent proposal, which was submitted in time to meet a July 31 deadline set by Pacific Gas & Electric to review and consider including it as part of the company’s plan for surrendering its license for the aging Potter Valley project.

PG&E plans to issue a draft surrender plan in November, so stakeholders and interested parties can review and comment on it. A second draft is to be circulated in May, with a final surrender plan scheduled for submission in January 2025 to the Federal Energy Regulatory Commission, which must approve it, spokesman Paul Moreno said.

The entities behind the proposal also must create a regional entity in short order, likely a joint powers authority, to govern and finance the project, which would require stakeholders to cover operating costs.

“There’s a lot more work that will need to be done moving forward,” Pauli said. “We have a pretty aggressive timeline for attaining goals in this effort.”

“We look forward to working with our partners in both the Eel River watershed and Russian River watershed and the environmental community to ensure that the decommissioning plan fully protects our Eel River fish and respects our federal fishing rights and water rights,” Whipple said.

You can reach Staff Writer Mary Callahan (she/her) at 707-521-5249 or On Twitter @MaryCallahanB.

Editor’s note: This story has been updated to correct the schedule for surrender plan circulation and submissions to federal regulators.

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