Officials gauge misting systems, falling river levels

An experimental vineyard-cooling project under way at Beaulieu Vineyard in Napa has caught the eye of the Sonoma County Water Agency for its potential to reduce the amount of water that grape growers draw from the Russian River watershed during the critical summer months.

Grapes are one of the most water-efficient crops grown in California, using just a few inches a year per acre under normal circumstances.

But with an estimated 61,000 acres of vineyards in the Russian River watershed in Sonoma and Mendocino counties, vineyards can have a significant impact on the river, especially when the weather doesn't cooperate.

"They're a big water user. No doubt about it," said Don Seymour, principal engineer for the Water Agency.

This past spring, when growers turned on their frost-protection systems, there were several days when the flow of the river was reduced by between 60 and 80 cubic feet per second, or more than a third of the river's total volume, Seymour said.

And last week, the river's flow dropped by 20 cubic feet per second -- nearly a fifth of its flow this time of year -- quickly plunging the river below the minimum level required by the state, Seymour said.

Grape growers are believed to be major contributors to this latest drop. Many turned on their drip irrigation and overhead sprinkler systems to protect the vines from the latest heat wave, which saw temperatures hit 110 in Ukiah and 106 downriver in Sonoma County's hot spot of Cloverdale.

When temperatures soar past 100 degrees, many grape growers cool their grapes the only way they can, using the same high-pressure overhead sprinkler system they use for frost protection.

But these systems use a lot of water, as much as 50 gallons per minute per acre.

An informal study conducted for the Water Agency by vineyard consultant Mark Greenspan concluded that about half of the vineyards in the Russian River region used water to cool grapes last year.

On average, growers turned on their sprinkler systems for only three days during the year, but that was enough to suck up plenty of water. Cooling vines this way drank 2 inches per acre, an improvement over the previous year, but still more than half of the amount used for irrigation during the rest of the year.

Since the Water Agency has no regulatory authority over vineyards, it is hoping to build relationships with the growers to better understand their water use, Seymour said.

This in turn will give the agency a better feel for how their water use affects the river, and help the agency make informed decisions such as when to release additional water from Lake Sonoma and Lake Mendocino.

"If we could reduce these swings, then we're in better control of the river environment," Seymour said.

If there's a way for growers to reduce their water use through systems like the one being studied in Napa, then the agency wants to share that information with growers.

Preliminary indications are that misting systems use between 11 and 22 gallons per minute -- less than half of the water consumed by overhead sprinklers.

Nick Frey, president of the Sonoma County Winegrape Commission, said the county's grape growers are already highly conservation-minded.

Moving water around is an expensive proposition, since most well pumps run on diesel generators, so growers already have a strong incentive to reduce their water use, he said.

Misters may provide them a way to do so even further.

"They'll absolutely save water over the sprinklers," he said.

The Water Agency already has committed $10,000 to the Napa study, and is considering how to bring a similar study to Sonoma County next year, Seymour said.

You can reach Staff Writer Kevin McCallum at 521-5207 or kevin.mccallum@pressdemocrat

.com.