Break in storm eases Russian River flood threat as reservoirs rise

A break in the storm is allowing swollen creeks and waterways to begin receding, reducing flood threats after days of a drenching rains closed several roads and kept residents hunkered down inside.

Though the lower Russian River was not forecast to crest until 10 p.m. Monday, it was not expected to reach even 28 feet in Guerneville, well below flood stage of 32 feet.

River levels farther upstream already have reached their peak and began falling around midmorning, though Highway 175 in Hopland remained closed due to river flooding, according to the CHP. The river also reached minor flood stage in the Geyserville area.

Much of Sonoma County remained under a flood warning set to expire at 7 p.m., National Weather Service meteorologist Dalton Behringer said.

But clearing skies and falling river levels mean reservoir managers will have a chance Tuesday to begin easing the pressure on Lake Mendocino and Lake Sonoma, which, while not as full as they were at their peak during successive atmospheric rivers last year, are well above target levels, said Nick Malasavage, chief of operations and readiness for the U.S. Army Corps of Engineer’s San Francisco District.

After holding inflow behind the dams until it was safe to release some of it, the Corps plans to bump up dam releases at both facilities beginning early Tuesday to create additional storage capacity for future storms, Malasavage said.

But both lakes could still hold more water were it needed, as proven last year when Lake Mendocino, currently at about 749 feet high, reached 753 feet in January 2023, he said. The water rose even higher after late-season storms that brought the level to 756 feet high in April and May.

The reservoir outside Ukiah held about 87,900 acre-feet of water on Monday, substantially more than the 68,000 threshold typically allowed at this time of year, though recent changes in reservoir management have allowed more water to accumulate depending on forecasts for future rain. An acre-foot of water equals 325,851 gallons, or about the amount of water needed to flood most of a football field one foot deep.

Lake Sonoma, which is substantially larger, stands at about 467 feet compared to a peak last March of 470. Though the difference is only a few feet it accounts for a large amount of stored water across the lake’s more than 4-square-mile surface.

The lake held about 289,000 acre-feet of water Monday, well over its historic winter target of about 255,000 acre-feet. The lake can hold 381,000 acre-feet if needed.

“In 2023, we experienced higher levels at both lakes,” Malasavage said.

A bit more rain is still in the forecast for Wednesday after a few scattered showers Monday and Tuesday as the bomb cyclone exits the region, Behringer said.

But rainfall totals Wednesday are likely to be under a quarter inch, with just a few tenths in many areas, he said.