Lake Mendocino reservoir at capacity; will use new water release guidelines

By John Ramos

A new approach for deciding when to release water from reservoirs is being used in the North Bay, and it could soon be applied to reservoirs across the nation.

The persistent rainstorms the past few weeks has Russian River swollen to its banks, and while other cities may see that as a flooding danger, in Healdsburg, they welcome it.  

Back in 2021, the drought was all anyone was talking about.

“The water shortage is the only topic of conversation on anyone’s mind right now,” said one man.

“It’s going to come to a point where we don’t have enough water for our city. And it’s got to that point,” said another.

“We’re in trouble. That’s all I can say,” said a third.

The reservoir had shrunk to the point where, from the boat launch, it looked like an open field of dirt and weeds. After two years of very little rainfall, Lake Mendocino had fallen to a level where it was in danger of not being able to release anything at all. Don Seymour, Sonoma Water’s Deputy Director of Engineering, said things got pretty dicey.

“So, the lake had a minimum of about 12,500 acre-feet,” he said. “And that’s only happened once before and that was in 1977. And so, that was a — I think everybody was getting pretty panicked at that point.”

Currently, Lake Mendocino sits at 109 percent of capacity, which means some water will have to be released. But the process for doing that has changed as well.  

In 2013, it rained really hard in December and then stopped for the rest of the winter. But by its own flood control guidelines, the US Army Corps of Engineers continued to release water until sometime in May, wiping out a lot of the summer supply.

Seymour said it got all the agencies involved thinking.

“Can these reservoirs be operated more efficiently, more resiliently?” he said. “And that’s what has led to this new operation at Lake Mendocino.”

The new system is called FIRO, short for “Forecast Informed Reservoir Operations.” Instead of just following mandated tables in a book, the Corps can now use long-range weather forecasts to help determine if it’s safe to keep more water in the reservoir. Seymour said it will probably save about 29,000-acre feet of water this year.  

That’s good news for Healdsburg, which has learned from experience that these times of plenty don’t always last.

“It’s just for the summer. We know that next summer we’ll be good,” said Public Works Director Larry Zimmer. “Whether there’s an impact on the following year really depends on how much rain or how little rain we get. But it’s always great to see it full. It makes everyone happy.”

Seymour said the new operating guidelines at Lake Mendocino have been so successful at conserving water that they are also being used at Lake Sonoma, with a plan for the US Army Corps of Engineers to extend them to other reservoirs across the nation.