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Site and Reach Assessment (pdf 3.4 mb)

Budget Information

SR 106 - Twanoh Falls Improvements

Twanoh Falls construction map
Click for full size map

The Twanoh Falls improvement project, located on State Route 106, replaced a culvert to improve creek flow, allowing for fish passage and reducing sediment buildup. The Twanoh Falls improvement project, located on State Route 106, replaced a culvert to improve creek flow, allow for fish passage and reduce sediment buildup.


October 2014

  • The new culvert is installed, crews have repaved the highway about six feet higher at the site to accommodate the larger culvert, and the previous 40 mile-per-hour speed limit has been restored.


This project is part of the Chronic Environmental Deficiency (CED) program. As part of an agreement with Washington Department of Fish and Wildlife, WSDOT is moving away from the repetitive repair of roadways that require recent, frequent and chronic maintenance repairs. Instead, WSDOT concentrates on long-term solutions that will optimize the improvements for fish and fish habitat, while also addressing transportation needs. 

View the 2008 Twanoh Falls Creek Site and Reach Assessment here (pdf 3.4 mb)

Why is WSDOT improving the Twanoh Falls creek area?
The highway crossing has had a long standing problem of sediment accumulation, requiring frequent excavation by maintenance crews to maintain creek flow and prevent flooding of the highway and adjacent properties. The sedimentation problem also poses fish passage problems.

The cause of these problems is because the previous culvert under SR 106 was too small. WSDOT  replaced the culvert with a structure of adequate size for flow, fish passage, and sediment transport.

The End Result
Replacing the existing culvert with a larger one improves creek flow, allows for fish passage and reduces sediment buildup.

Project Benefits
Reduced highway flooding:
The larger culvert and raised highway allows water to flow freely without sediment build up and flooding to the roadway. This will save money on frequent maintenance costs.

Environmental benefits:
Salmon and other fish need access to freshwater habitat for spawning and juvenile rearing. WSDOT recognizes that removing fish barriers is important to the restoration of fish habitat and salmon recovery efforts.

Since 1991, WSDOT has completed 283 fish barrier removal projects opening up over 970 miles of potential upstream habitat for fish.

Visit our Fish Passage project website for an interactive map of all barrier locations and project details.

What is the project timeline?
This project began in July and ran through October 2013.

Financial Information

Financial Data for PIN 310611A
Funding Source Amount ($ in thousands)
2003 Gas Tax (Nickel Funding) $0
2005 Gas Tax (TPA) $0
Pre-Existing Funds (PEF) $2,876
Total $2,876

Project signage will reflect the cost of construction engineering, project bid award and sales tax.

How can I get more information?
Michele Britton
Project Engineer

Claudia Bingham Baker
Olympic Region Communication Manager

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