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Lake Mendocino benefits from high-tech weather forecasting system

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Lake Mendocino made it through a typically long, hot summer with an abundance of water and now, thanks to an ongoing experiment with high-tech weather forecasting, the reservoir can retain more water through the winter, benefiting people, fish and farmers along the Russian River.

A dollop of spring rain pumped up the 3-square-mile reservoir near Ukiah, and water managers are now hailing the initial success of an experimental program intended to maximize storage in the second largest source of water for more than 655,000 people in three North Bay counties.

“It looks very promising,” said Jay Jasperse, chief engineer at Sonoma Water, the county agency that delivers Russian River water to 600,000 people in Sonoma and Marin counties. Another 55,000 people and nearly 43,000 acres of cropland from Mendocino County’s Redwood Valley to Healdsburg depend on water drawn from the river’s upper reach.

The new water management program, he said, aims to avoid the “mud puddle syndrome” that occurs when Lake Mendocino falls precipitously low in late summer and early fall.

Households, businesses and prime grape-growing areas, including Alexander Valley, rely on the reservoir, which is also the sole source of water needed to sustain federally protected fish in the upper river.

Officials say there are now about 8,000 more acre feet of water in the reservoir than there would have been without the program, which was implemented last fall.

That may not look like much to the casual observer, but it means more water for boaters and anglers on the reservoir and cooler water for the fish — all while maintaining its role in preventing floods.

“It was a doozy of a year,” said Nick Malasavage, chief of operations and readiness at the U.S. Army Corps of Engineers office in San Francisco, which controls wintertime operations at Coyote Valley Dam, built in 1958 on the east fork of the Russian River. “We prefer to keep things boring.”

High water in the lake kept the South Boat Ramp closed into late spring and Bushay Campground at the lake’s northeast end opened only two weeks ago.

Because Lake Mendocino’s primary purpose is flood control, the reservoir is usually held to 60 percent of capacity during the rainy season from November through February.

For the past 60 years, the reservoir’s operating manual has compelled water releases above the reservoir’s mandated wintertime level at 68,400 acre feet, or 22 billion gallons, to ensure there is sufficient space for inflow from winter storms.

Each acre foot is enough to supply an average California household of four for a year.

But that can be a dicey proposition, given the state’s propensity for swinging from flood to drought.

Local water managers haven’t forgotten the bitter experience of December 2012, when an atmospheric river dumped an unwanted 25,000 acre feet of water into Lake Mendocino.

Officials played it by the book, dumping the water down the Russian River as a precaution against more rain.

But the end of that storm marked the start of a prolonged drought that dropped Lake Mendocino to a mere 25,000 acre feet a year later, exposing vast expanses of dry gravel.

Atmospheric rivers, which deliver up to half of California’s precipitation each year, have been both a drought-busting blessing and a flood-causing curse to the Russian River region.

The 2012 experience drove Sonoma Water and the U.S. Army Corps of Engineers to seek a more refined way to manage Lake Mendocino.

Last fall, they activated a program devised by a cadre of scientists at UC San Diego using forecasting technology — computers, satellites, wind- and rain-measuring radar, weather balloons and sensors on land and sea — that did not exist when the dam and its rulebook were created in the 1950s.

“We had active weather (last winter) that allowed us to see how the system might work,” said Marty Ralph, director of the Center for Western Weather and Water Extremes at the Scripps Institution of Oceanography, which did the program’s scientific heavy lifting.

“It did what we hoped it would.”

Rep. Jared Huffman, D-San Rafael, who pushed for approval of the Forecast Informed Reservoir Operation program, or FIRO, said it was “proving to be a vastly superior operating strategy for facilities like Mendocino.”

The crux of the program is a formal “deviation” that allows the Army Corps to retain as much as 11,650 acre feet above the 68,400-acre-foot wintertime limit, depending on a reliable forecast of dry weather. FIRO also provides flexibility to manage flood risks by releasing water ahead of potentially major storms.

Jasperse said the program enables water releases “before rain starts hitting the ground,” while it is also a hedge against a repeat of the 2012 experience, when the reservoir was prematurely lowered.

Computer simulations using 32 years of weather history showed FIRO would be effective in wet and dry years, he said, but the “proof of concept” will await the outcome of the upcoming rain season.

“There are a lot of eyeballs on us,” Jasperse said, noting that two other facilities — Prado Reservoir in Riverside and San Bernardino counties and a pair of reservoirs in Butte and Yuba counties — are considering FIRO.

Lake Sonoma, the region’s major water source four times larger than Lake Mendocino, is better able to accommodate winter weather fluctuations, but FIRO could be adapted to it, as well, officials said.

Huffman said he would like to see the program made permanent “as soon as we can” to deal with potential changes in the relationship between the Eel and Russian rivers.

Climate change is also a pressing consideration, given the expectation of “more intense droughts and floods” in California’s future, Jasperse said.

You can reach Staff Writer Guy Kovner at 707-521-5457 or guy.kovner@pressdemocrat.com. On Twitter @guykovner.

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