U.S. Army Corps of Engineers is releasing water from Mud Mountain and Howard Hanson dams to create space for flood damage reduction operations.
As of 4 p.m. today Mud Mountain had inflows of 5,500 cubic feet per second (cfs) and was releasing 11,350 cfs. Howard Hanson had inflows of 4,600 and was releasing 7,900 cfs. Corps hydrologists expect the moderately high releases to continue through the next several days and could be adjusted as conditions warrant.
During the height of the flood event Mud Mountain operations reduced flood levels downstream in Puyallup by 4 feet. Inflows to Mud Mountain were as high as 29,000 cfs and releases at that time were held to 1,000 cfs.
Corps flood engineers will be on the job through the federal holiday and the weekend working with local communities to help with assessing damage to flood structures, make repairs and monitor saturated levees as waters recede. The conditions of many levees is unknown at this time due to a lack of access to some areas.
Levees damaged from over toping and erosion can fail when the flood waters recede and the Corps is working with the local communities to identify trouble spots, prioritize work and patch up those sites.
During this record rainfall event the Corps had flood engineers in seven river basins, has distributed more than 300,000 sand bags and continues to supply materials, equipment and assistance to communities as requested.
In the Snohomish/Stillaguamish basin, the Corps is assessing damage to French Creek and Marshland dikes and has placed rock at the Startup Levee on the Skykomish River which was damaged by overtopping. The river crested 8 feet over flood stage in the lower Snohomish basin, severely testing non-federal levees there.
The Skagit River basin flood team is monitoring levees at Fir Island, Lyman and Cockreham where crews placed sandbags and rock to shore up levees. The team has supplied ecology blocks to protect the Sedro-Woolley sewage treatment plant and placed rock adjacent to the Sauk River at Bryson Road at a section that was in danger of giving way.
In the Nooksack basin, engineers are assessing levees for damage and determining where repairs are needed.
In the Puyallup basin, several sections of levees breached, and crews continue to work in the Orting area to make emergency repairs.
The Seattle District Reservoir Control Center and Emergency Operations Center began 24-hour operation Nov. 5 and will continue to operate throughout the weekend.
Dams reduced flood levels significantly
Howard Hanson Dam on the Green River received peak inflows of 24,000, and the Corps held outflows to as low as 5,000 cfs, reducing the flood stage in Auburn by 7 feet.
Mud Mountain Dam operation reduced the flood stage downstream in Puyallup by more than 4 feet. Peak inflows to Mud Mountain Dam were 29,000 cfs, and the dam held outflow to less than 1,000 cfs.
During flood events, the Corps regulates Upper Baker, Ross and Wynoochee dams. The Corps is no longer regulating these dams.
In the Skagit River basin, Upper Baker and Ross dams inflows peaked at 39,000 cfs, and the Corps held flows to minimum outflows until the Skagit peaked, reducing the flood stage downstream at Concrete by about 5 feet.
When inflows peaked at Wynoochee Dam, the Corps held back about 13,000 cfs, reducing the river stage downstream by about 6 feet.
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