The Army Corps of Engineers was able to reduce flooding on the Skagit River with emergency operations of two hydropower dams upstream.

Big dams have big downsides, including killing salmon and drowning whole valleys under reservoirs.

But they also have major upsides, including climate-friendly electricity and, as became apparent last week, flood control.

As the Skagit’s flood waters were building, the Army Corps took over Ross Dam, a 540-foot tall concrete dam owned by Seattle City Light, and Upper Baker Dam, a 300-foot high concrete dam, owned by Puget Sound Energy.

The goal: holding back water to reduce flooding downstream.

As flows surged into the reservoir known as Ross Lake, engineers turned off Ross Dam spigot.

The dam held back 99% of water flowing into the reservoir, according to Army Corps officials.

Even that wasn’t enough to keep downstream flooding from breaking records.

But dam operations were able to shave 4 to 5 feet off the river’s peak height of about 37 feet, according to the Army Corps’ preliminary estimates.

“Without this strategic reduction, peak [river] stages in Concrete and Mount Vernon could have been much higher, leading to more severe flooding,” according to an Army Corps press release.

The waters of the Skagit basin are mostly wild, with 60% of the Skagit River’s flow never passing through a dam. Undammed tributaries include the Cascade, Sauk, Suiattle, and White Chuck rivers high in the North Cascades.

Seattle City Light spokesperson Jenn Strang said Ross Dam generated no hydropower during the Army Corps’ takeover. Two other City Light dams on the Skagit kept producing power.

After the flooding risk dropped on Friday, engineers started releasing water again to make space in the reservoirs for the next round of flooding.

The Army Corps returned control of Ross Dam to Seattle City Light over the weekend but took over the dam again as forecasters predicted river flows at the town of Concrete would rise past 90,000 cubic feet per second again.

News Source : https://www.opb.org/article/2025/12/16/army-takeover-of-skagit-dams-lowers-flood-waters/