Two dams in Washington state are being actively monitored by the Washington Department of Ecology’s dam safety division, as sustained rain has swelled and battered them with debris.
Over the past week, ecology engineers have repeatedly visited Lake Sylvia Dam near Montesano in Grays Harbor County, a site managed by Washington State Parks where cracks were discovered during an inspection earlier this year. There is no imminent threat to people if the dam were to fail, but property and infrastructure could be damaged, Department of Ecology spokesperson Andrew Wineke said in an email Monday.
Risks posed to the Lake Sylvia Dam have lessened in recent days, but the monitoring of them has not, he said. So far, waters behind the dam have stayed at levels below the emergency spillway.
That’s not the case at the Tortorice Dam, an earthen structure on private property near Sultan. An ecology engineer visited the site Monday as part of the ongoing work. The dam’s spillway is blocked with debris, so the Department of Ecology assisted the property owner in installing pumps to prevent it from overtopping. As of Monday evening, the pumps were effectively keeping water levels at a safe height.
Snohomish County Emergency Management and the Department of Ecology continue to monitor the dam closely. Several dwellings downstream from the dam could be at risk if it fails or breaches, but the situation is now stable and no evacuations have been ordered, Wineke said.
As rain returns to Western Washington this week and swells its dams, the U.S. Army Corps of Engineers is reducing their flows by withholding water to mitigate flood risk.
The corps announced Sunday it was reducing outflows from Howard H. Hanson Dam, 35 miles east of Tacoma, to spare the surrounding areas from further flooding. The trade-off is that holding more water than usual puts the dams at greater risk of breach or failure.
“The dams’ ability to protect downstream communities is lessened as more water is stored behind them,” the corps announced Sunday in a news release. “Communities will be at higher flood risk until all stored water is drafted.”
