Four rivers, four counties and nine levees. One of the busiest emergency levee repair seasons meant to safeguard life and property in Western Washington is nearing its end, but work remains before the start of the fall flood season. Repairs to the King County Mason Thorson Ells levee on the Middle Fork Snoqualmie River begins today, September 12, located near the popular "Blue Hole" recreation site in North Bend, Washington. The estimated two-week-long project will repair a 60-foot-long segment damaged in a 2020 flood event.
The $108,400 project is safeguarding a mix of property with an estimated value of $158 million. The river will remain accessible for boating use during construction. Under a cost-share agreement, U.S. Army Corps of Engineers (USACE) pays for 80% of the project and King County Flood Control District covers the remaining 20%.
In the damaged state the levees flood defense is reduced to a one-year flood level protection, or a 99% chance of flooding in any year. USACE will remove a portion of the damaged area then add embankment material and rock armor to restore the levee to its originally designed and built 10-year level of protection, or a 10% chance of flooding annually.
“The Middle Fork Snoqualmie River has recent flood history, so it’s imperative we tackle this repair quickly, ensuring people at-risk of a levee breach are protected,” stressed Janet Curran, USACE levee program manager. “The fully-restored levee will reduce risk to homes, private agricultural and public infrastructure in the area protected by the levee.”
Construction is taking place during the in-water work window of July 15 to October 31 to minimize impacts to local fish populations and follow best managed practices according to Curran, who is also an aquatic biologist. This project area is above Snoqualmie Falls, so there are no anadromous and federally listed salmonid species in the area. The local fish populations include mountain white fish, cutthroat and rainbow trout.
While construction impacts are expected to be minimal, the "Blue Hole" recreational area will be closed during repairs, and passing boaters are advised to be aware of their surroundings with construction ongoing. A memorial bench will also be temporarily moved during construction and placed in its original location when repairs are complete.
The project includes environmental measures meant to enhance and protect the surrounding natural wildlife and vegetation. USACE will remove invasive species and retain as much existing native vegetation as possible, while planting 10 native willow tree bundles every six feet. Nine Douglas fir trees will also be planted to compensate for removing one sequoia and two deciduous trees on the levee’s landward side.
Throughout the planning process USACE officials coordinated, consulted and worked with federal, tribal and state agencies, including: Environmental Protection Agency, National Marine Fisheries Services, U.S. Fish & Wildlife Service, Yakima Nation, Muckleshoot Indian Tribe, Snoqualmie Indian Tribe, Tulalip Tribes of Washington, Washington's State Department of Ecology, State Historic Preservation Office and King County.
To learn more about this levee project and other King County capital projects, visit: https://kingcounty.gov/depts/dnrp/wlr/sections-programs/river-floodplain-section/capital-projects