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Lake Mendocino is drying up, and 1,600 Russian River water rights are about to be halted

Trigger levels for Russian River curtailments

Lake Mendocino was at about 33% of capacity Friday, holding 28,120 acre-feet of water. An acre-foot is 325,851 gallons, or enough water to cover an area about the size of a football field with a foot of water.

The regulation allows curtailment orders to be issued for Russian River diverters only if lake storage falls below the following levels prior to the specified dates:

— 29,315 acre-feet before July 1

— 27,825 acre-feet before July 15

— 26,109 acre-feet before Aug. 1

— 24,614 acre-feet before Aug. 15

— 22,745 acre-feet before Sept. 1

— 21,251 acre-feet before Sept. 15

— 20,000 acre-feet on any date while the emergency regulation is in effect.

More about the Russian River system

The Russian River watershed takes in 1,500 square miles of landscape between Mendocino and Sonoma counties, with the 110-mile river at its center stretching from the headwaters north of Redwood Valley and Ukiah to Jenner, where it empties into the Pacific Ocean.

It is the lifeblood of communities throughout the region, providing water to more than 600,000 people served by Sonoma Water, which manages flows released from Lake Mendocino and Lake Sonoma, the basin’s two main reservoirs.

It also provides habitat for wildlife, including imperiled chinook and coho salmon and steelhead trout; supports a thriving outdoor recreational industry; and is critical to the region’s agricultural sector.

Flows in the Russian River are determined by runoff from rainfall, but also substantially by:

— Water diversions into the upper river from the Eel River, through the century-old Potter Valley powerhouse

— Management of the dams at Lake Mendocino, on the East Fork of the Russian River, and Lake Sonoma, which drains into Dry Creek, a tributary that meets the Russian River southwest of Healdsburg

For real-time river flow and reservoir information, visit sonoma.onerain.com.

Water supplies in Lake Mendocino are shrinking at a faster rate than they were a month ago, raising the risk the reservoir could be depleted by fall and setting regulators up to halt diversions from the Russian River for about 1,600 water rights holders before the end of July.

Two-thirds of those diverters, including farmers, ranchers, vineyard operators, rural residents and municipal suppliers, already were put on notice a month ago, when authorities said not enough water existed in the upper river to support irrigation, household use and the watershed’s imperiled fish species.

Now, amid the hottest and driest months of a deepening, two-year drought, regulators are poised to move forward with a more aggressive crackdown, called a curtailment of water rights.

It is likely to be unprecedented in scope, affecting hundreds of property owners along the upper river as well as public agencies, including the cities of Healdsburg and Cloverdale, that rely partly on the river for drinking water.

The action is meant to preserve minimal flows in the driest parts of the Russian River’s main stem and dwindling supplies in Lake Mendocino, which, like larger Lake Sonoma, hit record seasonal lows even in early spring.

Supplies behind Coyote Dam at Lake Mendocino are now dropping close to a key threshold that will trigger regulators’ move to halt downstream diversions.

Even as that grim scenario is unfolding, withdrawals from the river remain high between Cloverdale and vineyard-dense Alexander Valley.

That use has surprised water managers, especially after more than 900 water rights holders in the area were told starting last month that there was not enough in the upper river to sustain diversions for irrigation and household use. The notice stopped short of official curtailment but came with a host of potential fines — up to $1,000 a day or more based on quantity of water used.

“It was supposed to go the other way,” said Don Seymour, principal water engineer with Sonoma Water. “We were supposed to see a lot less water jumping out of there. And in some areas, we’re seeing that. And in some areas, we’re not seeing really any change from last year.”

River gauges show that consumption is heavy particularly between Geyserville and Jimtown, a lightly settled but heavily cultivated grape growing area north of Healdsburg.

Twilight pastels accentuate the meandering, uneven flow from the East Fork of the Russian River east of Ukiah, draining into the rapidly receding Lake Mendocino, Thursday, July 15, 2021 (Kent Porter / The Press Democrat) 2021
Twilight pastels accentuate the meandering, uneven flow from the East Fork of the Russian River east of Ukiah, draining into the rapidly receding Lake Mendocino, Thursday, July 15, 2021 (Kent Porter / The Press Democrat) 2021

Twice in recent weeks, Seymour said, dam managers at Lake Mendocino have had to send more water downstream to make up for flows that have gone missing along that particular stretch of the river and to ensure federally mandated minimum levels for the river’s diminished salmon and steelhead trout populations.

Those releases have made it likely that the all-important threshold at Lake Mendocino will be hit in the next 10-12 days, Seymour said.

Reduced diversions from the Eel River into Lake Mendocino account for part of the difference in reservoir storage, he said. Evaporation and uptake of the water streamside plants and trees are other factors, he said.

New state rules that took effect Monday allow state regulators ultimately to suspend the water rights of up to 2,400 landowners, ranchers, grape growers and others throughout the Russian River watershed, if conditions get bad enough.

The roughly 1,600 diverters in the upper river watershed would be affected first to safeguard supplies in Lake Mendocino.

The reservoir on Friday stored almost 9.2 billion gallons of water, or 28,120 acre-feet, down 195 acre-feet from Thursday. (An acre-foot is 325,851 gallons, or enough water to cover an area about the size of a football field with a foot of water.)

Under the emergency regulation, curtailments are triggered if the lake falls to 26,109 acre-feet by Aug. 1.

The Russian River watershed, which runs through Mendocino and Sonoma counties, supplies water to cities and towns along the river as well as to cities and districts served by the Sonoma Water Agency.
The Russian River watershed, which runs through Mendocino and Sonoma counties, supplies water to cities and towns along the river as well as to cities and districts served by the Sonoma Water Agency.

During the month of June, daily storage was declining by an average of about 145 acre-feet per day.

During the first week of July, the daily loss rose to an average 175 acre-feet.

If the state threshold is hit, water right holders would be allowed only enough water necessary to supply each domestic user with 55 gallons per person per day to meet minimum health and safety standards. Many still have access to groundwater wells or have other water rights permitting them to continue drawing on the river.

Ailene Voisin, spokeswoman for the State Water Board’s Division of Water Rights, said the agency was “encouraged” by the fact that storage levels in Lake Mendocino had remained above threshold targets so far.

“That being said, we’re cautiously watching depletions and releases from the reservoir, and note that both depletions and releases have picked up over the last week or so,” Voisin said. “We’re now entering the time of the year when depletions and use are greatest, and based on projections there’s a significant chance that the threshold targets could be reached by the end of the month.”

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

Trigger levels for Russian River curtailments

Lake Mendocino was at about 33% of capacity Friday, holding 28,120 acre-feet of water. An acre-foot is 325,851 gallons, or enough water to cover an area about the size of a football field with a foot of water.

The regulation allows curtailment orders to be issued for Russian River diverters only if lake storage falls below the following levels prior to the specified dates:

— 29,315 acre-feet before July 1

— 27,825 acre-feet before July 15

— 26,109 acre-feet before Aug. 1

— 24,614 acre-feet before Aug. 15

— 22,745 acre-feet before Sept. 1

— 21,251 acre-feet before Sept. 15

— 20,000 acre-feet on any date while the emergency regulation is in effect.

More about the Russian River system

The Russian River watershed takes in 1,500 square miles of landscape between Mendocino and Sonoma counties, with the 110-mile river at its center stretching from the headwaters north of Redwood Valley and Ukiah to Jenner, where it empties into the Pacific Ocean.

It is the lifeblood of communities throughout the region, providing water to more than 600,000 people served by Sonoma Water, which manages flows released from Lake Mendocino and Lake Sonoma, the basin’s two main reservoirs.

It also provides habitat for wildlife, including imperiled chinook and coho salmon and steelhead trout; supports a thriving outdoor recreational industry; and is critical to the region’s agricultural sector.

Flows in the Russian River are determined by runoff from rainfall, but also substantially by:

— Water diversions into the upper river from the Eel River, through the century-old Potter Valley powerhouse

— Management of the dams at Lake Mendocino, on the East Fork of the Russian River, and Lake Sonoma, which drains into Dry Creek, a tributary that meets the Russian River southwest of Healdsburg

For real-time river flow and reservoir information, visit sonoma.onerain.com.

Mary Callahan

Environment and Climate Change, The Press Democrat

I am in awe of the breathtaking nature here in Sonoma County and am so grateful to live in this spectacular region we call home. I am amazed, too, by the expertise in our community and by the commitment to protecting the land, its waterways, its wildlife and its residents. My goal is to improve understanding of the issues, to find hope and to help all of us navigate the future of our environment. 

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