Dry winter spurs water managers to cut Russian River flows to retain reservoir supplies

In a stark reminder that drought has once again taken hold on the North Coast, Sonoma County is preparing to ask state water regulators for permission to reduce water levels in the Russian River this summer to conserve water stored in Lake Mendocino and ensure minimal late-season flows for fish.

The request, to be filed with the State Water Resources Control Board as soon as this week, comes in recognition that the inland areas of Mendocino County, where Lake Mendocino retains runoff into the upper Russian River, has had less than half the normal rainfall this year.

In addition, supplemental flows from the Eel River have been reduced under a separate move by PG&E, further straining supplies that would normally help replenish Lake Mendocino and sustain water levels in the upper Russian River. Those flows support farmers, imperiled salmon and steelhead trout and municipal supplies stretching downstream to Healdsburg.

In a bid to retain reserves across the system, Sonoma Water, the region’s main wholesaler, is also set to reduce flows on the lower Russian River below the confluence with Dry Creek, the outlet for Lake Sonoma.

The combined impact means water managers, just 15 months after historic flooding on the lower Russian River, are having to maneuver to safeguard drinking water supplies for up to 600,000 Sonoma and Marin county residents, while also lowering minimal flows to ensure enough water exists for salmon and steelhead through the year.

“It’s been a really dry year … the third-driest year for the last 127 years,” said Don Seymour, principal engineer for Sonoma Water, the county water agency. “We don’t take it lightly to file with the state board to change the minimum in-stream flow.”

The agency is required to maintain certain flow rates in the upper and lower reaches of the river, as well as Dry Creek, which flows into the river downstream of Healdsburg.

During normal dry-year ?conditions, the minimum flow between July 1 and December would be 75 cubic feet per second from Lake Mendocino to the confluence with Dry Creek and 85 cfs from Dry Creek to the Pacific Ocean at Jenner.

Sonoma Water is requesting permission to reduce releases from Lake Mendocino to 50 cfs in the upper river and 60 cfs in the lower river. The agency is seeking permission to drop even lower - to 25 cfs and 35 cfs in the upper and lower stretches, respectively - if storage in Lake Mendocino drops to a critical level.

The plan is similar to one pursued on three successive occasions during the last drought to the dismay of anglers and those who depend on river recreation to draw tourists. Already, those businesses are suffering greatly amid the pandemic shutdown.

“We can’t catch a break this year,” said Sonoma County Supervisor Lynda Hopkins, who represents the lower river.

Reduced water levels also means slower moving water, raising concerns about the potential for harmful blue-green algae blooms, Hopkins said.

“Of course, the concern is always water quality,” she said. “Lower slower, shallow in combination with high temperature and, of course, nutrients are what results in toxic algal blooms.”

But water agency officials said there’s little choice.

Where Santa Rosa recorded a paltry 17.82 inches of rain since Oct. 1, about 59% of the 30-year average, Ukiah had just 14.66 inches, less than half the average, National Weather Service meteorologist Steve Anderson said.

The area around Lake Pillsbury, which supplies Eel River water for PG&E’s Potter Valley hydroelectric project, was especially dry this year, which is why the utility since May has reduced diversions through its project and into Lake Mendocino.

“It’s probably going to be about 40 percent less water per month from the Potter Valley diversion,” Seymour said.

Lake Mendocino still has more than 77% of its water supply, however, because the U.S. Army Corps has agreed in recent years, including last winter, to be more flexible about scheduled flood control releases through more carefully calibrated operations spearheaded by the corps, Sonoma Water, Scripps Institute and other partners.

“We’re actually in much better shape at Lake Mendocino than we would have been normally for such a dry year,” Seymour said. “We would actually be in much worse a situation than we were in 2013.”

Lake Sonoma, the region’s largest reservoir and main source of drinking water, sits at about 87% of its capacity.

The U.S. Drought Monitor last week showed all of Sonoma and Mendocino counties in the “severe drought” category.

The public will have an opportunity to comment on the petition when it is filed with the State Water Resources Control Board. The order would last a maximum of 180 days and would likely go in effect July 1.

You can reach Staff Writer Mary Callahan at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.