Suspected Green River landslide prompts reduction in dam release


January 14, 2009 · 1:10 PM

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An apparent landslide along the banks of the Green River, a few miles from Flaming Geyser Park in south King County, is diverting flows of the river.

The U.S. Army Corps of Engineers, Seattle District, has dispatched flood engineers to the area to assess the situation and will work with local officials to respond.

In response, the Corps, which operates and maintains the Howard Hanson Dam along the Green River for flood control, is decreasing flows from 8,000 cubic feet per second to 7,000 cfs. The decrease in outflows from the dam will make flows on the Green River at Auburn approximately 9,500 cfs.

During a post-flood assessment Tuesday, engineers at the dam discovered a depression on the right bank, requiring the reservoir pool be brought down in order to investigate further. As of Wednesday morning, engineers were on site beginning that assessment.

The reservoir-pool level was 1,173 feet before the start of flood-water evacuation Tuesday night. The Corps needs to bring the level down to 1,150 feet in order for maintenance engineers to safely address the depression issue; therefore, the higher river flows at Auburn can be expected to last until approximately Friday.

Emergency managers with King County have been briefed and this is not considered an imminent emergency. Flood Engineers from the Corps will be walking the levee system along the Green River 24 hours checking for integrity issues until the dam reaches its targeted reservoir level.

The Seattle District will continue to work with local officials and will provide public updates via media alerts, on its Web site (www.nws.usace.army.mil) and via its information line at 1-866-562-2635.

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