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The Tolt River levees and the State Route (SR) 203 road force the Tolt River to flow through a single, narrow bridge opening. The current configuration of the bridge limits the amount of water that can pass under the bridge and increases upstream flood risks. During a major flood, SR 203 north of the bridge becomes flooded, blocking the southern entrance into and out of the City of Carnation. Logs and other woody debris get caught up on the bridge, increasing flood risks.

The SR 203 Bridge Improvements Feasibility Study will evaluate the opportunities, costs, and benefits of providing increased flood water flow through the SR 203 Bridge and road as you approach the bridge. The study will evaluate modifications to the existing bridge and/or the addition of culverts or additional bridges north of the existing bridge to reduce flooding on SR 203.

The study will focus on the lower Tolt River south of the City of Carnation in the vicinity of the SR 203 Bridge.

SR 203 Bridge Improvements Feasibility Study Factsheet - 2.3MB PDF

aerial map of SR 203 study area
Project Area
aerial map of January 2015 Tolt River Flood and SR 203
Tolt River - January 2015 Flood
Photo of January 2009 flood closure of SR 203 north of the bridge
January 2009 flood closure of SR 203 north of the bridge


  • Investigate opportunities to provide increased hydraulic conveyance through the State Route (SR 203) Bridge and road embankment to reduce or eliminate flood impacts to SR 203 caused by overtopping flows in the right bank floodplain.
  • Engage with the tribes, residents, landowners, the City of Carnation, WSDOT, and other interested parties to identify ideas and concerns about improving hydraulic conveyance through the SR 203 bridge and road embankment.
  • Integrate the SR 203 Bridge Improvements Feasibility Study with three other concurrent studies on the Tolt River: Tolt River Level of Service Study, Tolt River Sediment Management Feasibility Study, and Lower Frew Levee Setback and Floodplain Reconnection Feasibility Study.


Benchmark Date
Project planning Early 2019
Data collection and technical studies Spring - Summer 2020
Develop and evaluate alternatives Summer - Fall 2020
Evaluate costs, benefits, and permitting requirements for each alternative Fall 2020 - Winter 2021
Draft study report Spring 2021
Finalize study report and share with public Summer 2021


Tolt River Corridor Planning and Capital Investment Strategy website

About the King County Flood Control District 

The King County Flood Control District is a countywide special purpose government created to protect public health and safety, regional economic centers, public and private properties, and transportation corridors. The members of the King County Council serve as the governing body for the District. The Water and Land Resources Division of the King County Department of Natural Resources and Parks carries out the approved flood protection projects and programs for the District under an interlocal agreement. Information is available at the King County Flood Control District.

For more information about the SR 203 Bridge Improvements Feasibility Study, contact Jay Smith, Project Manager, King County River and Floodplain Management, Water and Land Resources Division, Department of Natural Resources and Park.