A dam more than a century old in Lake Sylvia State Park in Grays Harbor County is “showing signs of increasing stress,” the county’s emergency management department said Tuesday.
The dam, which is east of Aberdeen and north of Montesano, hasn’t failed, “but could continue to worsen if weather conditions persist,” the department said.
The dam appeared to be a significant hazard to nearby roads and property, said Jimmy Norris of the Washington State Department of Ecology. There is no safety concern for people, should the dam fail, as there are no nearby residences at risk.
Nevertheless, Washington State Parks advised residents in the Sylvia Creek area downstream in Montesano to prepare for additional flooding and be prepared to move on short notice.
Up to an inch of rain is forecast for Montesano through Thursday night as the atmospheric river tapers out, according to the National Weather Service. East of Lake Sylvia, the Satsop River is under a flood warning and forecast to see minor flooding Wednesday night.
Incoming rain may cause the lake’s level to rise again, Washington State Parks said, despite water levels receding about a foot between Monday and Tuesday. The lake’s level has yo-yoed over the past couple of days.
Cracks in the dam were identified by crews during their most recent inspection earlier this year. The dam was partially reinforced between 1988 and 1995 after it was built in 1918, said Washington State Parks spokesperson Sarah Fronk.
Lake Sylvia was lowered five feet to the height of its reinforced section in response to the inspection.
A consultant’s report from November and December last year noted that “the dam was not stable and there was a potential risk of failure,” Norris said.
Washington State Parks has closed Lake Sylvia State Park due to public safety concerns, Fronk said. Though the park is still accessible via numerous trail systems on government and private properties, the agency is urging visitors to stay away.
A mudslide occurred at the park’s entrance, Fronk said. Though it has since been cleared, conditions “can change on a dime.”
Montesano received more than 5 inches of rain in the 48 hours before the county emergency management’s announcement Tuesday, according to NWS.
The extent of the “stress” put on the dam as a result of the rainfall is unclear, Fronk said.
There have been “no visual structural changes” to the dam as a result of the recent rains, Washington State Parks said. Crews are continuously monitoring it and will conduct an official inspection after the weather clears.
The agency said it “installed an electronic monitoring system and implemented safety protocols for high-water events” and is currently developing a scope of work to “further assess the dam and identify long-term solutions.”
Crews are on site clearing logs and debris from the water and dam spillways, and monitoring the dam and its water levels, Washington State Parks said.
