By Steven Schauer, Deputy Executive Director and King County Staff
The King County Flood Control District (KCFCD) has been working diligently since its creation in 2007 to safeguard our communities from flooding. The KCFCD, in collaboration with King County as service provider, has spearheaded over 370 capital projects aimed at mitigating the risk of levee and revetment failures. These projects, along with the operation and maintenance of over 500 flood protection facilities, cover 118 linear miles and approximately 800 acres of land crucial for flood mitigation.
While the KCFCD’s weekly blog typically shares information about new and ongoing projects, each month, we will shine a spotlight on a completed project that is quietly doing its job to safeguard our community against the threat of flooding. The project we’re covering this month is the Sinnema Quaale Upper Project between Duvall and Carnation.
Reconstructing for Resilience: The Sinnema Quaale Upper Project
Nestled along the Snoqualmie River between Duvall and Carnation, the completed Sinnema Quaale Upper Project stands as a testament to the KCFCD’s commitment to safeguarding community resources and enhancing local ecosystems. Originally constructed using repurposed materials, the project site has undergone a significant transformation since its 1961 inception, evolving from a practical but rudimentary flood control measure to a comprehensive, multi-functional infrastructure asset.
Fun fact: the original repurposed material utilized to construct the revetment was used car bodies – the site was known locally as the “car body curve.”
Why Rebuild?
Over the years, the Snoqualmie River’s powerful floodwaters and shifting riverbanks compromised the original car-body revetment, weakening slope stability and threatening critical infrastructure along a 1,000-foot stretch of the river. The bank’s erosion endangered the popular Snoqualmie Valley Trail, a buried regional fiber-optic line, and nearby State Route 203 (SR 203), which serves as a crucial transportation link for local communities. To address these threats, King County, as service provider to the KCFCD, designed a solution that would not only protect essential infrastructure but also foster healthier aquatic habitats along the river.
Designing a Robust Solution
Collaborating with Herrera Environmental Consultants, the KCFCD and King County conducted a comprehensive analysis of twelve potential designs, weighing factors such as cost, effectiveness, habitat improvement, and hydraulic performance. The result was an innovative, layered revetment that combines strength with environmental stewardship. The river-facing structure is built primarily from wood, supported by timber piles to enhance habitat conditions and natural aesthetics. Behind it, two steel sheet-pile walls and a structural earth wall stabilize the slope, supporting both the trail and embankment.
Achieving Project Goals
The reconstructed Sinnema Quaale Upper Revetment now stretches approximately 750 linear feet and effectively shields the Snoqualmie Valley Trail, fiber optic infrastructure, and SR 203. This layered design approach improves slope stability and significantly reduces the risk of erosion, even during heavy flooding. The structure has already withstood several high-water events, confirming its resilience and long-term durability. The project also successfully incorporates environmental enhancements, providing a better habitat for fish and other aquatic species by creating a more stable and naturalized riverbank.
“We have taken a critical step toward safeguarding both our infrastructure and natural resources for the Lower Valley communities with the completion of the Sinnema Quaale Upper Project,” said Sarah Perry, King County Flood Control District Vice Chair. “This project embodies our commitment to resilient, forward-thinking solutions protecting essential roads against erosion as well as the associated fiber optic cables to ensure communication lines stay open, all while enhancing the ecological health of the Snoqualmie River. It’s a powerful example of how we can prioritize public safety, support regional connectivity, and foster environmental stewardship all at once, and I’m excited to have been a part of it.”
Community and Environmental Benefits
In addition to safeguarding vital transportation and communication resources, the Sinnema Quaale Upper Project enriches the area’s recreational and ecological value. Protecting the Snoqualmie Valley Trail means preserving a beloved pathway for hikers, cyclists, and nature enthusiasts. Moreover, the project’s focus on habitat-friendly materials reflects the dedication of the KCFCD and King County to supporting the region’s biodiversity.
With projects like Sinnema Quaale Upper, the KCFCD, together with King County, continues to innovate and prioritize sustainable infrastructure that serves the needs of both people and nature. This undertaking not only mitigates flood risks but also enhances the resiliency and quality of life in the Snoqualmie River Valley. As we look to the future, the KCFCD remains committed to projects that support vibrant, sustainable, and flood-resilient communities.