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SE 472nd Street Culvert Replacement Project
Construction of this project is expected in Summer 2025
The current metal pipe culvert under SE 472nd Street is rusted and at risk of failing. A new, much larger, concrete box culvert will be constructed to stabilize the road. The new culvert will also be easier for fish to pass through and creates an additional one and a half miles of useable habitat for fish.
Status update
Winter 2025
Construction requires an eight (8) week road closure. We plan to begin work in July 2025. Please check this website and sign up to receive email/text notifications about the project at Road Alerts.
Project overview
King County will replace a narrow, worn-out metal pipe culvert with a much larger and wider concrete box culvert under SE 472nd Street. The improvements will stabilize the road and make it easier for fish to pass under SE 472nd Street and continue their migration to and from the White River.
The existing metal pipe culvert is wide enough to prevent the road from flooding. However, it is rusted and old and must be replaced before it collapses. If the pipe collapsed the force and volume of the water could cause the entire roadway to fail.
Construction will take approximately two months during summer 2025. The limited work area requires the county to close both directions of SE 472nd Street between 261st Ave SE and 268th Ave SE for up to eight straight weeks to install the culvert underneath the road.
There will be no through access whatsoever when the road is closed, and alternate routes will be available for all travelers including cars, trucks, bicycles, and pedestrians.
Why is King County replacing this culvert?
We are replacing the narrow metal culvert because it has outlived its useful life.
Rust has eaten away at the bottom of the metal pipe, and it must be replaced before it fails.
Benefits of the concrete box culvert
Concrete box culverts have many benefits, including durability, strength, and ease of installation.
The new box culvert will accommodate a much larger volume of water and has a longer lifespan than a metal pipe.
Road closure information
SE 472nd St will be closed to all vehicles, bicycles and pedestrians for most of summer 2025.
There will be no official detour route for this project because there are many alternate routes and travelers will use alternate routes to go around the closure.
Alternate routes include:
- SE Mud Mountain Road
- 248th Way SE
- SE 464th St
- 268th Ave SE
What to expect during construction
During the eight-week closure, crews will:
- Dig a large pit in the road to remove the existing four-foot metal pipe and prepare for the installation of the new culvert.
- Using a large crane, crews will place the bottom and sides of the new culvert in the ground. Then they will place natural materials inside of the box culvert. It will be made to resemble a streambed making it easier for fish to pass through when they return to the area after additional barriers have been removed.
- The crane will return and lower the lid of the culvert into place.
- Finally, crews will rebuild and pave the road.
The project team will work to prevent dust and dirt caused by construction work from spreading in the air and water. In addition, people living near the work area might experience the following while the culvert is being removed and replaced:
- Noise and odor from saw cutting, jackhammers, excavators, generators and pumps.
- Trucks hauling materials to and from the construction site.
- Large construction cranes in the roadway.
After the new culvert is opened to traffic, crews will continue low impact restoration work including native landscaping and site clean-up.
Budget and funding sources
This $2 Million project is funded through the Fish Passage Restoration Program.
Frequently asked questions
The existing metal pipe culvert is wide enough to prevent the road from flooding. However, it is rusted and old and must be replaced before it collapses. If the pipe collapsed the force and volume of the water could cause the entire roadway to fail. The proposed culvert will reduce flood elevations upstream of the culvert.
The existing metal pipe will fail if it is not replaced soon. Now that it is time to replace it, the county is replacing it with a larger box culvert that is built to current road and stream crossing standards that require a much larger culvert that can accommodate a natural stream bed.
The existing metal pipe culvert is 48 inches (4-feet) in diameter. The new box culvert will be 16-feet-wide, 8.5-feet high and 40-feet long.
It will take approximately eight weeks to remove the old pipe and install the new box culvert under the road.
The existing metal pipe is deteriorating and will fail if it is not replaced soon. If the pipe is not replaced and fails, this will cause roadway hazards to drivers.
Fish have not been observed at this culvert due to a significant barrier to fish passage downstream. Design work on replacing this downstream barrier has begun, however the SE 472nd culvert began first due to the deteriorating condition of the pipe. Once this and the additional downstream barrier are removed there are several species of fish that will have their historic access to this stream restored.
A fish passage barrier is anything that makes it difficult for fish to swim upstream or downstream.
Many fish barriers in unincorporated King County are round pipes (culverts) that channel streams and water underneath the road. Many of these culverts were installed between 30 and 100 years ago. These older culverts allow water to flow but are so narrow and steep that they prevent fish from swimming through them.
This project, in partnership with the Department of Natural Resources and Parks Fish Passage Program, will make it easier for fish to pass under SE 472nd Street once additional barriers are removed. Deteriorating culverts and other barriers block fish passage and undermine the state and county recovery efforts.
The new culvert and creek habitat restoration is designed to move water through at its natural pace, just like a real stream.
Pipe culverts may block fish migration because the water flow is too swift, too shallow, or the culvert is perched too high above the stream.
The ability of salmon and trout to swim upstream to their traditional spawning grounds is vital to their recovery across Washington and King County.
One of the most effective ways to ensure the survival of native fish – and the southern resident orcas that rely on them as a food source – is to remove barriers to their habitat.
The following fish species are found in the White River Basin. There is the potential for these fish to return to the tributary under SE 472nd Street after barriers in the system are removed.
- Winter steelhead trout
- Bull trout
- Coho salmon
- Chum salmon
- Chinook salmon
- Resident cutthroat trout
