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 Sammamish River Bank Repair Project in Bothell.
Restoring Resilience: The Sammamish River Bank Repair Project
The Sammamish River has long been a vital natural and recreational resource for King County residents. Stretching 13.9 miles from Lake Sammamish to Lake Washington, this federal flood protection facility is not only a key flood management structure but also a beloved recreational corridor. In 2018, the Sammamish River Bank Repair Project addressed critical deficiencies in two segments of the river’s right bank to ensure continued flood protection and safeguard the adjacent Sammamish River Trail.
“The Sammamish River Bank Repair Project is a shining example of how we can protect urban infrastructure while enhancing our natural environment,” said King County Flood Control District Supervisor Rod Dembowski. “This project not only safeguards communities and critical trails in north King County but also supports salmon recovery efforts, a vital part of our region’s ecological heritage. By funding initiatives like this in urban areas, the King County Flood Control District demonstrates its commitment to equitable investment in flood risk reduction and environmental stewardship across all corners of the county.”
Project Objectives
The primary goal of the Sammamish River Bank Repair Project was to restore the integrity of two compromised segments—the West Site (downstream) and the East Site (upstream)—spanning 720 linear feet of riverbank. This effort was critical to maintaining the pre-damage level of flood protection for local communities, infrastructure, and the environment.
Secondary objectives included:
- Reducing risks to trail users along the Sammamish River Trail.
- Enhancing habitat in alignment with the Sammamish River Corridor Action Plan and WRIA 8 Salmon Recovery Plan.
- Implementing a self-mitigating design for sustainable riverbank management.
Background and Challenges
The Sammamish River’s current form dates back to the 1960s, when it was dredged and straightened by the U.S. Army Corps of Engineers (USACE) as part of the Channel Improvement Project. While effective for flood mitigation, these modifications altered the natural dynamics of the river, increasing the risk of erosion and habitat degradation.
During regular annual inspections of the Sammamish River, King County’s River and Floodplain Management staff identified significant sloughing in two sections of the right bank. (King County is the KCFCD’s primary service provider.) The condition worsened in 2017, necessitating emergency riprap placement to mitigate immediate risks to the Sammamish River Trail. A comprehensive repair was clearly needed to restore stability and address long-term concerns.
Design and Considerations
The project team navigated a complex set of constraints and opportunities to develop a robust design:
- Key Design Objectives:
- Stabilize the riverbank to maintain flood protection.
- Safeguard trail users by addressing erosion risks.
- Integrate habitat-friendly features, including engineered log structures and native vegetation.
- Challenges:
- Limited space for bank stabilization and trail realignment.
- High-traffic areas requiring extensive safety and traffic control measures.
- Regulatory requirements, including a narrow window for in-water construction (July 1–August 31).
Four design alternatives were assessed, balancing stability, ecological benefits, and feasibility. The KCFCD approved a “soft touch” approach for the West Site, emphasizing habitat restoration and monitoring opportunities. For the East Site, where erosion risks were greater, the KCFCD approved the implementation of more substantial stabilization measures, including engineered log structures.
Implementation and Results
Construction, carried out by Trimaxx Construction, Inc., began in July 2018 and concluded in October 2018. Highlights of the repair work include:
- West Site: The emergency riprap was removed, and the bank was reshaped with a gentler slope. Native plants were installed, and a small alcove below the Ordinary High Water Mark was created to enhance fish habitat. The adjacent trail alignment was also modified slightly to accommodate the new bank profile.
- East Site: With its location on an outside river bend, the East Site required reinforced measures. The bank slope was flattened, the trail was realigned, and engineered log structures were installed at the river’s toe to ensure stability and provide refuge for Chinook salmon and other fish species.
Advancing Sustainability and Safety
The Sammamish River Bank Repair Project exemplifies the KCFCD’s commitment to balancing infrastructure needs with environmental stewardship. By enhancing aquatic habitat while mitigating flood and erosion risks, the project not only protects local communities and trail users but also contributes to regional salmon recovery efforts.
We’re proud of this collaborative effort that brought together innovative engineering, ecological enhancement, and thoughtful planning. The Sammamish River and its surrounding communities are more resilient thanks to these improvements, ensuring this treasured resource remains sustainable for generations to come.