Sunday, January 29, 2023

Army Corp of Engineers Holding Back the Rising Waters of Lake Mendocino to Prevent Flooding in Hopland and Western Sonoma County

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A flooded vineyard in Hopland [Picture by Matt LaFever]

For now, federal officials are planning to hold back releases from the rapidly filling Lake Mendocino because of continuing high water flow downstream on the Russian River.

High river flows are still threatening to flood areas at Hopland and the historically vulnerable Guerneville area in western Sonoma County.

“We are going to hold back the stormwater for now,” said Nick Malasavage. He is chief of the Operations and Readiness Division of the U.S. Army Corps of Engineers district headquarters in San Francisco.

Malasavage said Lake Mendocino, while it has reached its annual capacity for water storage, is capable of holding back significantly more runoff if needed. 

“We have room available to manage it for flood control now, and help ease the threat of flooding downstream,” said Malasavage.

More rainfall is expected this weekend but Corps officials, who assume control of the lake’s management once water levels enter a so-called flood pool, believe the lake can handle more heavy inflow.

Lake Mendocino’s waters, muddy with silt [Picture by Mike Geniella]

“The rise in the lake’s level in just the past month is dramatic (30 feet) but it is designed to hold more, and historically has before releases are made, said Malasavage.

Malasavage said the Corps’ goal is to ‘never contribute to downstream flooding.’

While Guerneville suffers periodic flooding from surging inflows into the Russian River downstream from Coyote Dam at Lake Mendocino, the man-made reservoir north of Ukiah is critical to limiting flood damage.

Lake Mendocino is believed to hold back the equivalent of an additional one foot of water that might reach Guerneville when the Russian River floods.

Lake Mendocino was created in 1950 for flood control and water supply. It was a joint project of the Army Corps and the Sonoma County Water Agency which secured 87 percent of the water stored in the lake for domestic, fisheries, and irrigation supplies. The agency has since constructed Lake Sonoma on Dry Creek, and now serves 600,000 customers in Sonoma and northern Marin counties. 

A family looks out over the rising waters of Lake Mendocino [Picture by Mike Geniella]

Mendocino County declined to participate in the Coyote Dam building project. A Ukiah Valley special district ended buying rights to only 8,000 acre feet of the available water for local use.

The Russian River watershed in total, unlike most Northern California fed by Sierra Nevada snowpack, relies only on rain, and a small diversion from the Eel River for hydroelectric power production. 

Typically, rainfall on the North Coast is enough to replenish annual supplies and keep streams flowing healthily for fisheries. But the drought of the last three years sent water levels plunging, including in Lake Mendocino. Gov. Gavin Newsom used the dry flatbeds of Lake Mendocino as a backdrop for a highly public drought emergency proclamation in April 2021.

The unexpected but steady rainfall since Christmas is replenishing lakes and reservoirs and ending fears of another summer of low lake levels and little recreation uses. Lake Mendocino and Lake Pillsbury upstream on the Eel River are popular visitor attractions during good weather months.

Malasavage and other water officials credit a more sophisticated weather forecasting system called FIRO, developed with the help of the Scripps Institute of Oceanography and first implemented at Lake Mendocino, for being able to balance the demands of water supply and flood control.

“Right now, we can sit tight and see what happens over the next several days,” said Malasavage.

Malasavage, an East Coast native who has a doctorate from Drexel University in civil/geotechnical engineering, has more than a professional interest in the Russian River, and its effects on the region.

“My family and I live in Forestville in Sonoma County. I keep an eye on things,” said Malasavage.

Innovations in forecasting methods over the past 25 years, and new ways of looking at a region’s hydrology, allow for new federal confidence.

“We are better able to refine our management techniques. We don’t have to just build more dams to do that,” said Malasavage.

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