Potter Valley Hydroelectric Project License Expiration Paves The Way For Eel River Dam Removal Plans

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The future of a little-known dam on the Eel River in Lake County could be shaped this year as the license expires for a failed PG&E hydroelectric project that plays a vital role in supplying water to 600,000 residents from the counties of Sonoma and Marin.

The demolition of the Scott Dam, a 138-foot concrete structure built a century ago to impound Pillsbury Lake, is an “absolute requirement” for a coalition that includes the counties of Sonoma, Mendocino and Humboldt interested in the getting the permit, said Rep. Jared Huffman, Congressman from the North Coast.

But the coalition – known as the Two-Basin Partnership – failed to fundraise and plan the complex and costly process of taking over the project owned and operated by Pacific Gas & Electric since 1930.

This is not a David vs. Goliath competition. PG&E gave up its interest in the small unprofitable power plant in Mendocino County’s bucolic Potter Valley in 2019. When the federal licensing agency opened the door to new owners, only the partnership registered interest. .

It now faces an April 14 deadline to submit an application to the Federal Energy Regulatory Commission.

“It’s very close,” said Pam Jeane, deputy managing director of Sonoma Water, the county agency that supplies water to more than 600,000 residents in parts of Sonoma and Marin counties.

The power plant’s turbines produced just 9 megawatts of electricity, which is about 0.1% of PG&E’s total 7,700 megawatts, before a recent shutdown due to a transformer failure. PG&E has not decided to replace it, a spokesperson said.

Water from the Eel River now flowing around the closed power plant and into the headwaters of the Russian River, however, is critical to sustaining farms, ranches, vineyards, and thousands of rural residents.

The Scott Dam is located 11 miles upstream of the much smaller Cape Horn Dam, which collects water at the entrance to a kilometer-long tunnel dug into a mountain and a series of pipes that divert approximately 20 billion gallons of water per year from the Eel River into the Potter Valley Power Plant, completed in 1908.

The diversion, which critics see as a water intake that tapers the wild and scenic Eel River, turned 7,000 acres of Potter Valley into a cornucopia producing $ 34 million in wine grapes, pears, livestock and other products per year.

Flowing south into the eastern branch of the Russian River, the diverted water flows into the Lake Mendocino reservoir near Ukiah and eventually into the main branch of the Russian River, supporting agriculture worth 743 million dollars from Redwood Valley to the famous Alexander Valley wineries near Healdsburg.

Sonoma Water relies on the Diversion to provide mandatory flows for federally protected fish in the upper Russian River.

Maintaining the diversion is “very critical,” Jeane said.

Without it, Lake Mendocino would be “constantly lower and would likely empty in four out of ten years,” according to the agency’s studies, she said.

Upper Russian River flows would decline to “similar or worse” than the paltry levels seen last year, Jeane said.

The diversion typically adds 60,000 acre feet of water per year to the river, while Sonoma Water has delivered an annual average of 45,591 acre feet to its customers over the past five years.

One foot-acre is equivalent to 326,000 gallons, or a year’s supply for about two households.

The premise of the Huffman-organized coalition is that Eel River’s interests would be served by the removal of the Scott Dam while the diversion to the Russian River is maintained – hence a “two-basin solution”.

The biggest loss would be Pillsbury Lake, a 2,300 acre recreational reservoir deep in the Lake County portion of the Mendocino National Forest, about 100 miles from Santa Rosa.

The Potter Valley Project is a holdover from the Old West, born in 1905 when a San Francisco entrepreneur had the answer to Ukiah’s quest for an alternative to burning coal for electricity at the county seat and commercial center of the Mendocino County with approximately 2,000 residents.

WW Van Arsdale had discovered a point at the northern end of the Potter Valley where a narrow ridge separated the upper reaches of the Eel River from the upper reaches of the eastern fork of the Russian River, about 475 feet below.

He drilled a tunnel eight feet in diameter for a mile through the mountain and built the pipes and penstocks that supplied gravity-weighed water to turn the turbines at the power plant that began to operate in 1908.

The Scott Dam, built to provide a year-round water supply to the Eel River, completed the Potter Valley project in 1922.


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