Transportation / Municipal & Federal
Tillicum Creek Fish Passage Culverts
*Replacement of four undersized pipe culverts under a state route with bottomless precast arch structures, restoring access to 11 miles of upstream salmon and steelhead habitat.
- Client
- Cascadia Regional DOT
- Engineer
- Northbank Engineering Group
- Location
- Chehalis, WA
- Value
- $5M–$25M
- Delivery
- Design-Bid-Build
- Status
- Completed
- Completed
- 2023
Spec sheet
By the numbers
- Structures
- 4 precast arches, 28 to 44 ft spans
- Total precast
- 1,240 LF
- Streambed material
- 3,800 CY engineered mix
- Excavation
- 31,000 CY
- Habitat restored
- 11 stream miles
- Contract value
- $14.6 million
Story
Challenge, solution and outcome
Challenge
Four culverts on a 1.8-mile stretch of the highway were blocking fish passage under a court-ordered barrier correction schedule. Each site required full-depth excavation of the roadway, in-water work and a temporary diversion of a live stream in a 10-week window.
The highway carried 11,000 vehicles per day, and detours for the log haulers ran 24 miles.
Solution
We prepared a work sequence that kept two sites in active construction while the others stayed open, using temporary signals and a single-lane alternating pattern. Streams were diverted through pumped bypass lines after fish salvage by a qualified biologist, and arches were set within 36 hours of excavation reaching grade.
The engineered streambed was placed in lifts and compacted with water flushing, and woody debris and boulder clusters were installed to match the habitat design.
Outcome
All four crossings reopened 29 days ahead of schedule. Spawning surveys the following fall counted coho and steelhead redds upstream of the old barriers for the first time in the agency's records, and the owner has since used the project as a model for its next barrier correction packages.
The crew worked 71,000 hours with 0 lost-time incidents and zero fish-handling mortalities.
Safety
Safety highlights
- 0 lost-time incidents over 71,000 work hours
- Excavation protection with precast-arch setting plan for each site
- Fish salvage by qualified biologists with zero mortalities
- Temporary signal system with no reportable traffic incidents
From the owner
“These four crossings were on a court deadline, and the crew delivered them with a month to spare. The stream restoration looks like it has always been there.”
Gallery
Project gallery
