Trees called threat to King County river levees

Large trees must be removed from 19 King County river levees before they damage the earthen structures that hold back raging water during storms, the Army Corps of Engineers said Thursday.

King County has more levees at risk of failing than any other state except California, where 37 levees have been identified as suspect, according to a Corps of Engineers list obtained under a Freedom of Information Act request, The Associated Press reported. All of the endangered levees in Washington are in King County.

Levees on parts of the Green, Cedar, Tolt and Snoqualmie rivers received "undesirable" ratings from the federal government because of "excessive riverward vegetation and large trees that threaten the structural stability," Corps of Engineers Seattle District Commander Col. Michael McCormick wrote in a letter to County Executive Ron Sims.

Sims said the county will follow the Corps' instructions, as it did on the Green River in Tukwila, where the federal agency asked for the removal of large trees. A larger number of smaller trees are being planted on the levee.

"We're going to meet their standards," Sims said. "If we've got to remove trees, we'll continue to do that, but we'll replace those trees with far more than we take out — I can assure you of that."

Trees have been a source of friction between the county, which wants some trees to improve habitat for endangered chinook salmon and other animals, and the Corps, which warns that large trees will weaken levees if they are uprooted.

Paul Komoroske, chief of the Corps' Emergency Management Branch in Seattle, said thick vegetation on some King County levees has made it impossible to inspect the structures thoroughly. "Once they cut the trees," he said, "we'll determine whether they need to put more rock on it or something else."

The County Council last month adopted Sims' flood-control plan, which calls for spending up to $335 million over 10 years to repair or rebuild substandard levees.

Several Snoqualmie River levees failed during heavy rains in November, and levees or flood walls on the Green and Cedar rivers received damage.

Pam Bissonnette, county director of natural resources and parks, said the November storms showed problems worse than excessive vegetation. "To us, the actual movement and failure of slopes, undercutting and washing away of banks, is of much more concern than speculation about whether a bush or a tree is going to do something," she said.

Keith Ervin: 206-464-2105 or kervin@seattletimes.com