This King County map of the Green River shows where gages are to monitor levels starting at the Howard Hanson Dam. COURTESY GRAPHIC, King County

This King County map of the Green River shows where gages are to monitor levels starting at the Howard Hanson Dam. COURTESY GRAPHIC, King County

Army Corps running emergency operations, deploys spotters on Green, White rivers

Levels continue to rise with constant rain

  • Thursday, February 6, 2020 3:21pm
  • News

The U.S. Army Corps of Engineers, Seattle District, is running its Reservoir Control and Emergency Operations centers 24 hours per day and sending spotters to monitor conditions on the Green and White rivers, addressing current weather conditions and increasing reservoir storage at two Corps dams near Enumclaw.

Inflows are predicted to be as high as 27,500 cubic feet per second (cfs) at Mud Mountain Dam on the White River and 22,000 cfs at Howard A. Hanson Dam on the Green River, according to a Army Corps news release Thursday afternoon. These inflows are within the scope of what the dams are designed to handle, but Corps staff must manage the reservoir storage space carefully to prevent overfilling the reservoirs.

“Earlier this week we were pushing outflows to reduce both dam’s pools and make reservoir space,” said Western Washington senior water manager Jon Moen. “We are now again storing water to reduce outflows and greatly reduce flood risk on those rivers as the event ramps up.”

Moen expects inflows to peak late Thursday or early Friday morning.

“This is a significant event with the potential to reach inflow levels not seen in over 10 years,” Moen said.

Mud Mountain Dam releases are expected to be around 6,000 cfs. Completed in 1948, the dam’s single authorized purpose is managing flood risk and typically does not store a pool, except during flood events. When completely filled, the reservoir stretches 5.5 miles, covering 1,200 acres.

The Corps’ White River spotters will be in the Pacific and Sumner areas monitoring conditions because of unpredictable channel capacity there. Historically, large channel capacity losses have happened in these areas.

Moen and Corps water managers are regulating Howard Hanson Dam releases to target Green River flows up to 12,000 cfs at the Auburn gage. Completed in 1961, the dam’s primary purposes are flood control in the winter, and fish enhancement and water conservation in the summer. During winter, the reservoir is kept nearly empty for flood risk reduction.

“Corps river spotters are integrating with King County to assist with monitoring and assessing conditions on 30 miles of Green River levees,” said Seattle District Emergency Manager Doug Weber.

Public Law 84-99 enables the Corps to assist state and local authorities in flood fight activities and cost share in the repair of flood protection structures. The purpose is to prevent loss of life and minimize property damage associated with severe weather.

“Public safety is the Corps’ number one priority,” said Weber. “Our authorities allow us to work with state and local governments. Private citizens should contact their local government for assistance.”

King County’s Emergency Blog is currently live at

Phase 3 level on Green River

King County issued a notice Thursday morning that the Green River is in flood phase 3.

Moderate flooding is expected in rural lowland areas. Urban areas of the Green River Valley are generally protected by the levee system. Be aware that flood conditions can change rapidly.

For more information, go to

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