A new project to address several longstanding flood control and habitat issues on the Sammamish River at its outlet from Lake Sammamish in King County's Marymoor Park is the focal point of a County-sponsored meeting, set for June 27.
A new project to address several longstanding flood control and habitat issues on the Sammamish River at its outlet from Lake Sammamish in King County’s Marymoor Park is the focal point of a County-sponsored meeting, set for June 27.
The outlet from Lake Sammamish into the Sammamish River is marked by a shallow concrete weir and a straight, rock-lined channel, 200 feet wide and extending 1,500 feet downstream from the weir. This area, known as “Willowmoor,” is also referred to as the “transition zone” where the lake becomes the river.
These transition zone features are specifically designed to pass flood flows quickly downstream, and to help maintain summer lake levels for recreational uses, while still allowing for upstream fish passage, including salmon returning to the Issaquah Hatchery from their time in saltwater.
The meeting is scheduled for 6:30-8 p.m. at Clise Mansion in Marymoor Park, 6046 W. Lake Sammamish Pkwy. At the meeting, staff will discuss the history of the transition zone, what problems this Sammamish River project is trying to solve and how interested citizens can stay involved and updated as the project design and construction moves forward.
A project website with a variety of resources is at www.kingcounty.gov/rivers; click on “Projects” on the left-hand navigation bar, then scroll down the alphabetized project list to “Willowmoor.”
King County is forming a stakeholder committee to provide input on the project, including recruiting members to represent interests of the general public. To volunteer, or for more information about this project, contact Craig Garric or call 206-263-0495.
Historically the Sammamish River meandered through floodplain wetlands, which provided natural storage and release of spring flood waters. When the floodplain wetlands were ditched and drained for agriculture during the last century, their flood storage function was lost.
Consequently, to address springtime flooding, the U.S. Army Corps of Engineers in 1964 straightened and deepened the Sammamish River and created the transition zone.
Through agreement with the U.S. Army Corps of Engineers, King County operates and maintains all Sammamish River flood control facilities, including the transition zone.
The transition zone is not sustainable in its current condition and configuration. In order to ensure the transition zone’s capability to pass flood flows, County crews must perform intensive and costly maintenance including mowing, removing riverside plants and sediment removal.
These maintenance practices degrade habitat and water quality and conflict with the Endangered Species Act, as well as federal, state and local goals to protect ecological functions and species.
The Willowmoor project is multi-purposed: Ensure the transition zone’s long-term capability to continue providing essential flood control for the Sammamish River and Lake Sammamish, while reducing maintenance costs and improving water quality and habitat conditions.
This goal will be accomplished by modifying up to a half-mile of the river channel in and upstream of the transition zone, and utilizing undeveloped King County land adjacent to the west bank of the river channel. Modifications could include widening and realigning the channel with more natural meanders, or possibly constructing a second “habitat friendly” channel with meanders and pools adjacent the flood control channel.
The existing weir or a similar replacement and the reconstructed channel will continue to maintain summer lake levels and control lake outflow. Other features may be included to enhance habitat and public access.
Habitat diversity and conditions are expected to continue to improve as a result of natural ecological and river processes once the project has been completed.
The first phase of the project – planning and preliminary design – is funded by the King County Flood Control District and the City of Redmond, and will be completed in coordination with King County Parks, the Muckleshoot Indian Tribe, and lakeside property owners.
Funding for final design and construction will be pursued following completion of this first phase, and will likely include Flood Control District funds combined with federal and state grants.
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The King County Flood Control District is a special purpose government created to provide funding and policy oversight for flood protection projects and programs in King County. The Flood Control District’s Board is composed of the members of the King County Council. The Water and Land Resources Division of the King County Department of Natural Resources and Parks develops and implements the approved flood protection projects and programs. Information is available at http://www.kingcountyfloodcontrol.org/.