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 SR 169 Flood Risk Reduction Project along the Cedar River.
Rebuilding Resilience: The SR 169 Flood Risk Reduction Project
When heavy rains fall in King County, the stretch of State Route (SR) 169 near Cedar Grove Road has historically transformed into more of a lake than a street. Flooding in this critical corridor has created hazardous road conditions, isolated homes, and closed a vital route that connects communities along the Cedar River. Thanks to the KCFCD—and in partnership with King County, Washington State Department of Transportation (WSDOT), and the Cedar River community—flooding at this location is now a challenge of the past.
“I’m proud to support the SR 169 Flood Risk Reduction Project,” said Reagan Dunn, Chair of the King County Flood Control District. “It’s a project that delivers important long-term benefits for nearby homes and businesses while also caring for our environment. By addressing the root causes of flooding in this critical corridor, we ensure that first responders and everyday commuters can rely on this route—especially when it matters most.”
Project Background and Site Context
Flooding along SR 169, just north of the Cedar Grove Road intersection, has caused repeated road closures in 2009, 2015, and 2020. These events didn’t just inconvenience commuters—they isolated nearby residences and created major public safety concerns. Closure of this road results in a detour of up to six miles to Renton and three miles to Maple Valley, delaying emergency response and affecting hundreds of daily drivers.
To investigate the cause of these issues, a feasibility study was completed in 2019. It revealed that the cause of roadway flooding wasn’t the Cedar River overflowing—but an undersized and partially blocked storm drainage system that couldn’t handle runoff during high-intensity rainfall events. Blockages were worsened by sediment buildup and beaver activity, and the existing culverts were also identified by WSDOT as fish passage barriers.
A Smart, Sustainable Solution
Completed in Fall 2021, the SR 169 Flood Risk Reduction Project replaced the existing 18-inch culverts beneath SR 169 and the Cedar River Trail with much larger 15-foot-wide box culverts. These improvements now allow stormwater to move efficiently from upland areas to the river, even during severe storms. The system is now built to function up to a 100-year storm event and beyond —dramatically reducing the risk of highway flooding and improving access to homes, schools, and emergency services.
A 100-year storm event is also known as a 1% annual chance storm event.
More Than Just a Road Fix
This project goes beyond protecting asphalt. By eliminating fish passage barriers, the new culverts open access to potential off-channel habitat, providing ecological benefits alongside transportation and safety improvements. It’s a win-win for salmon and people.
Additionally, the project is compatible with WSDOT’s long-term vision to widen SR 169—readying this section of highway for the future growth and mobility needs of our region.
Moving Forward
The successful completion of the SR 169 Flood Risk Reduction Project is a testament to what thoughtful engineering, strong partnerships, and community-focused planning can accomplish. By reducing flood risk, restoring ecological function, and ensuring safe access along a vital roadway, this project reinforces the King County Flood Control District’s commitment to protecting people, property, and the environment.