Storage behind Hanson Dam helps prevent flooding in Kent

The U.S. Army Corps of Engineers Seattle District helped fight flooding in Kent and other cities over the past couple of weeks.

Seattle District Commander Col. Kathryn Sanborn gave updates on the district’s flood response efforts, during a joint press conference in Kent with Gov. Bob Ferguson, according to a Dec. 20 Army Corps news release.

The press conference came on the heels of the district’s response to back-to-back atmospheric river storms and record-breaking flooding that impacted Washington over the past two weeks.

Sanborn discussed the structural integrity of the state’s levee systems and ongoing management of federal dams, including the Hanson Dam on the upper Green River, which helps protect Kent, Auburn, Renton and Tukwila, and the Mud Mountain Dam along the White River.

“We operate Howard A. Hanson and Mud Mountain Dams to provide flood risk reduction in the valleys downstream,” Sanborn said. “We were successful in those efforts during this flood event. Storing a record amount of water behind Howard A. Hanson Dam, for example, prevented an additional 5 feet of floodwater in the Green River at Auburn, which would have overtopped nearly all the levees.”

The Army Corps’ Reservoir Control Center has managed prolonged high inflows at Howard A. Hanson and Mud Mountain Dams, significantly reducing the peak crests of the Green and White rivers to prevent catastrophic downstream flooding, according to the news release.

Outlining the application of Public Law 84-99, which allows the Army Corps to provide emergency assistance for flood fight efforts and repair eligible flood control works, the district commander said:

“We also recognize that sustained high flows puts pressure on the banks, levees, and other infrastructure. As we always do, we will operate our dams over the next few days with public safety of the entire valleys at the forefront. That means a slow and smooth decrease of outflows, so that we manage both levee function and reservoir elevations as we prepare for future storm events. The risk of levee failure decreases as the river levels drop, but it does not go away.”

Together with their local partners, the Army Corps will continue monitoring several areas around the Green and White river basins, and coordinating on potential emergency actions, upon request.

“Looking forward, it appears we may be seeing less precipitation in the forecast,” Sanborn said. “While the Green and White rivers will start to slowly come down in coming days, it’s still important for the public to know that water levels will stay above normal for several days.”