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Water and Land Resources Division

King County, Washington

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Water and Land Resources Division, King County, Washington

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Willowmoor Floodplain Restoration Project 

Project area

The project will modify the Lake Sammamish Transition Zone, which is at River Mile 13.0-13.5 on both banks of the Sammamish River. 
Click to enlarge the map of the Willowmoor Project Area in PDF. 


The project began in 2012 and with a 30 percent project design expected to be completed by 2014. Permitting and construction will be scheduled following the initial design phase of the project. 


  • Historically the Sammamish River meandered through wetlands, which provided natural flood storage and release. That function was lost when the river was straightened and dredged in the 1960s, and adjacent land was developed and drained.
  • The outlet of Lake Sammamish is now a straight, armored channel, 200 feet wide and extending 1,500 feet downstream, constructed by the U.S. Army Corps of Engineers in 1964.
  • The Lake Sammamish Transition Zone includes a weir to maintain summer lake levels.
  • Crews currently maintain the area by mowing and removing riverside plants; maintenance could include removing sediment. Intensive maintenance is required annually to maintain channel capacity. 
  • These maintenance practices harm habitat and water quality and conflict with federal, state and local goals to protect ecological functions and species listed under the Endangered Species Act.
  • The desired outcome is to maintain flood control functions in a way that improves water quality and habitat conditions.

Project facts

  • The project will alter the Transition Zone and use adjacent undeveloped King County land to improve natural complexity and habitat values while reducing maintenance costs and allowing sustainable flood control for the Sammamish River and Lake Sammamish.
  • The alterations will include widening the channel and possibly restoring the river’s natural meander to reconnect it to its restored channel or wetlands.
  • The existing weir or a similar replacement and reconstructed channel will continue to keep lake level stable and control outflow.
  • The habitat diversity of the channel and the river system will be improved by these engineered changes, but also by natural ecological processes that will occur over time in the new conditions.
  • The project will be completed in coordination with King County Parks and Recreation, the City of Redmond, the Muckleshoot Indian Tribe, and lake-side property owners.
  • The U.S. Army Corps of Engineers must approve these changes as part of the Sammamish River Flood Control Project built in 1964. 

Public involvement

A public meeting was held on June 27, 2013 at Marymoor Park to kick-off the Willowmoor Project. Staff discussed the history of this reach, what problems the project is trying to solve and how to stay involved and updated as the project design and construction moves forward. View the presentation (PDF, 2MB).

King County has convened a Stakeholder Advisory Committee to provide input through 30 percent design of the project. Membership will represent park users, property owners, environmental interests, tribes, local, state and federal jurisdictions and the public at large. For more information contact contact Craig Garric.

Project documents

(For help viewing PDF files, see Acrobat Help page.)

External links

For more information about the Willowmoor Floodplain Restoration Project, please contact Craig Garric, Project Manager, King County River and Floodplain Management Section.