SEATTLE -- U.S. Army Corps of Engineers (USACE) water managers are conducting 24-hour operations for five dams to reduce downstream flood risk as a series of powerful, back-to-back atmospheric rivers deliver overwhelming rainfall across Western Washington.
USACE owns and operates Howard A. Hanson (Green River) and Mud Mountain (White River) dams. But to better coordinate regional flood response, Seattle District is regulating Ross Dam (Seattle City Light), Upper Baker Dam (Puget Sound Energy), and Wynoochee Dam (Tacoma Public Utilities), under established agreements allowing USACE to regulate waterflow for city and utility-owned dams during flood events.
“Our Reservoir Control Center is fully activated, and our teams are working around the clock to regulate flows at Howard A. Hanson, Mud Mountain, Ross, Upper Baker, and Wynoochee dams,” said Kyle Comanor, the district’s Western Washington senior water manager.
Seattle District’s water management officials took over regulating Ross Dam at 2:00 p.m., Dec. 8, Upper Baker Dam at 2:00 p.m., Dec. 8 and Wynochee Dam at 7:00 p.m. Dec. 8.
The public should consult their local or county emergency management officials for the latest information on their specific area.
“Public safety is our absolute number one priority” said Krystle Walker, Seattle District emergency management chief. “This is an extremely dangerous weather event, and conditions can change rapidly. We urge everyone, especially those living near rivers or behind levees, to stay vigilant, be prepared and have a “go kit” ready.”
While USACE officials saw receding inflows to dams on Tuesday evening, Dec. 9, inflows picked up again today, Wednesday, Dec. 10 at the front end of the atmospheric river.
“We are using every available bit of storage space in these reservoirs to capture floodwater and lessen the impact on downstream communities, but residents need to prepare for sustained high-river levels,” said Comanor.
As the Skagit River basin braces for record flooding, USACE is regulating Ross and Upper Baker dams to absorb as much of the peak flow as possible.
Forecasters expect river flows at Concrete, Washington, to reach 213, 000 cubic feet per second (cfs) early on Thursday, Dec. 11 – more than double the threshold for major flooding. While Ross and Upper Baker will help shave off the peak flow, residents will still see unprecedented river levels.
On the White River, Mud Mountain Dam will store a massive amount of water, with the reservoir potentially reaching its highest level on record. Seattle District water managers forecast inflows to peak at 31,000 cfs. To preserve storage space, they targeted a release of 7,000 to 7,500 cfs on Dec. 10 and will continuously evaluate throughout the week.
These operations are critical to reducing flood risk for the communities of Pacific, Sumner and Puyallup.
Howard A. Hanson Dam continues to balance storage with downstream levels on the Green River. To maintain space for a forecast peak inflow of 25,000 cfs, they’ll manage releases to keep the river at Auburn flowing around 10,000 to 11,000 cfs.
For additional information, King County’s Emergency Blog is currently live at https://kcemergency.com, and Pierce County residents can visit www.co.pierce.wa.us/dem.
The National Weather Service issues flood watches and warnings and should be consulted for that information at https://www.weather.gov/sew. Visit https://water.noaa.gov/wfo/sew to see updated Western Washington river levels and monitoring info.
The public can also find reservoir data for Corps-managed dams online at https://www.nwd-wc.usace.army.mil/nws/hh/www/index.html. Reservoir data for Corps-managed dams is available online at: https://www.nwd-wc.usace.army.mil/nws/hh/www/index.html.