Feds OK extra storage at rising Lake Mendocino

Russian River water managers and consumers they serve in Mendocino, Sonoma and Marin counties got a break Wednesday from the prospect of watching precious water flow to the ocean from the rapidly filling Lake Mendocino reservoir near Ukiah.

Raised to more than 97 percent of storage capacity by last weekend’s deluge, the reservoir was on the verge of crossing a threshold that would require the Army Corps of Engineers, which operates Lake Mendocino’s Coyote Dam, to begin releasing water in an effort to preserve the reservoir’s ability to prevent flooding in the event of another major storm.

The last time that happened was in December 2012, when a multi-day downpour brought the reservoir to the 94,000-acre-foot level, cutting deeply into the flood protection pool that tops out at 116,500 acre-feet.

Unfortunately, there were no major storms for the next five months, deepening a statewide drought now entering its fourth year.

During the drought, the Army Corps has been trapped in an uncertain game each rainy season, attempting to balance the conflicting goals of impounding enough water in reservoirs to get through another hot, dry summer without jeopardizing the capacity to prevent springtime flooding should the storm doors swing wide open.

It’s a tricky proposition, said Jay Jasperse, Sonoma County Water Agency’s chief engineer, because “everybody knows we have pretty variable weather here.”

It’s also a game that local water managers and Rep. Jared Huffman, D-San Rafael, hope to improve by overhauling the Army Corps’ rule book.

Two weeks into February, the stakes are as high as they get in the North Bay.

On Wednesday, Lake Mendocino was at 66,551 acre-feet : Just shy of the 68,400-acre-foot threshold that would, under the Army Corps’ operations manual for the lake, trigger mandatory releases from Coyote Dam.

The lake had gained 8,000 acre-feet of water since Friday and had a “good chance” of surpassing the threshold with continued runoff from the weekend storm, Jasperse said.

In Ukiah, Sean White, general manager of the Russian River Flood Control and Water Conservation Improvement District, was bracing for a repeat of 2012, when about 24,000 acre-feet of water was released from Lake Mendocino. An acre foot is 325,851 gallons and is generally described as enough water to sustain a family of four for a year.

Relief came Wednesday in the form of an email from the Army Corps’ San Francisco District office advising White that the “minor deviation” he had sought from the Lake Mendocino operations plan had been approved, allowing the reservoir to store an additional 5,825 acre-feet of water.

“It’s smaller than I wanted but it’s not peanuts either,” White said. “I’ll take that all day long.”

The Corps rebuffed his request last year for a 17,000-acre-foot deviation, but said a smaller one could be considered, White said.

The deviation means Lake Mendocino can impound up to 74,200 acre-feet of water without triggering a release, he said. The extra 5,800 acre-feet is about what his water district customers from Redwood Valley south to Hopland used last year while conserving “like crazy,” White said.

The Ukiah-based district holds the rights to 8,000 acre-feet of water in Lake Mendocino.

Meanwhile, the tight limit on Lake Mendocino’s water supply pool will ease in just 16 days.

Starting March 1, the threshold for mandatory water releases - known as the “rule curve” - starts increasing by 600 acre-feet per day, boosting the threshold to 111,000 acre-feet in May and holding it there until October.

Hence, the best case scenario would be a wet month of March, Jasperse said.

Lake Sonoma, about four times larger than Lake Mendocino, held 213,629 acre-feet of water Wednesday, at 87 percent of capacity and comfortably below the release threshold at 245,000 acre-feet , officials said.

The Sonoma County Water Agency draws water from both reservoirs to supply 600,000 customers in Sonoma and Marin counties. In the fall, releases from Lake Mendocino not only satisfy human needs but also provide cool water for endangered fish in the Russian River.

Both local water agencies are backing Huffman’s bill, nicknamed the FORECAST Act, which would update the Army Corps’ 60-year-old operations manual for Lake Mendocino with a dose of modern meteorological science.

The revision would prevent “the untimely and wasteful release of water” that can be dictated by the current rigid rules, Huffman said. His bill would require the Corps to consider revising the operations plan by incorporating satellite weather data from the National Oceanic and Atmospheric Administration regarding the prospects for heavy rain.

Satellite data can’t say exactly when a so-called atmospheric river will arrive, but it can reliably indicate when there isn’t one “on the horizon,” avoiding unnecessary releases of stored water, Huffman said.

The North Coast congressman announced Tuesday that he had reintroduced the bill, which he offered last year. As ranking Democrat on the House Natural Resources Subcommittee on Water, Power and Oceans, Huffman said he will “do everything I can” to get the bill to a vote.

Mike Dillabough, chief of the operations and readiness division for the Army Corps’ San Francisco District, said he can’t express an opinion on Huffman’s bill. But, he said, the Corps and is already considering how it might make use of the weather data, while NOAA is assessing the accuracy of its atmospheric river forecasts.

Reservoir operating standards require data that is “highly reliable,” Dillabough said. “The last thing you’d want to do,” he said, is get caught by a storm that pushes water over the top of a dam.

In February 2006, a storm swelled Lake Mendocino from about the level it’s at today to around 114,000 acre-feet , bringing water uncomfortably close to the spillway that handles an overflow, Dillabough said.

It takes about two days to release 10,000 acre-feet of water from Lake Mendocino, maintaining flow rates that don’t cause damage downstream on the Russian River, he said.

Given the water storage deviation approved Wednesday, he said there probably won’t be any flood control releases from Lake Mendocino this season - barring another major storm or two.

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