No safety hazards found in dams at Lake Sonoma and Lake Mendocino, Army Corps says

The two dams stockpiling a total of more than ?100 billion of gallons of water in Sonoma and Mendocino counties are holding steady amid the deluge of rain this winter, with no safety concerns detected, federal officials said Tuesday.

That message was delivered to a commander for the federal agency overseeing dams in the southwestern United States as part of his visit to Lake Sonoma.

Col. Peter Helmlinger, who leads the United States Army Corps of Engineers’ South Pacific Division, came to Lake Sonoma to check the status of the reservoir and Warm Springs Dam, where the volume of impounded water this week reached the highest level since January 1995, topping out at 125 percent of seasonal capacity.

“Col. Helmlinger oversees 60 to 70 dams and other projects, and we’re high on his list,” said Mike Dillabough, chief of the Operations and Readiness division for the United States Army Corps of Engineers’ San Francisco Division.

“Our dams are doing just fine. We haven’t identified any safety hazards,” Dillabough said. “Sonoma rates really well. On a scale of one to five, with five being ‘perfect’ and one meaning ‘run for your life,’ Lake Sonoma is a four.”

The visit comes in the aftermath of the failure of an emergency spillway at the Oroville Dam in Butte County that triggered the precautionary evacuation of nearly 188,000 people who live downstream of the reservoir and could have been affected by a collapse of the damaged spillway. Dams and reservoirs across the state have faced increased scrutiny in the wake of the emergency.

The Army Corps’ rating system ranges from a one - considered “critically near failure” - to a five, which carries some “residual risk considered tolerable,” according to agency documents. Only one dam in the country has been given a rating of five, Dillabough said.

Coyote Valley Dam at Lake Mendocino scored a three but could be upgraded to a four because of ongoing maintenance and upkeep, he said.

Lake Mendocino and Lake Sonoma undergo annual inspections by both the Army Corps and the Sonoma County Water Agency. Every five years, the Army Corps conducts an “aggressive” inspection and every 10 years the dams are inspected “like they never had been done before,” Dillabough said.

He drew a contrast between Lake Oroville, the state’s second-largest reservoir, and the two local reservoirs, which he said had more available space to absorb runoff from future storms.

“Unlike the Lake Oroville Dam, the dams here were both for flood protection as opposed to water storage,” he said. “Thirty-five to 60 percent of the space in Lake Sonoma and Mendocino reservoirs are water pools for flooding. Oroville only had 20 percent of space for flood protection.”