This illustration shows the preliminary design of the new US Highway 101 span across the Duckabush Estuary.

Image courtesy of the Washington State Department of Fish and Wildlife

The saltwater marsh below US 101 will be restored following construction of the new span.

Image courtesy of the Washington State Department of Fish and Wildlife

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Washington state continues to refine design plans for replacing the US Highway 101 bridge that spans the Duckabush Estuary. A new and taller span, officials say, will improve wildlife habitat while reducing flooding in the network of channels and streams that flow into Hood Canal.

At a recent online update of the state and federal highway reconstruction project, officials said some of the land that’s needed to remove and replace the existing lanes of US 101 and bridges that cross the estuary has already been purchased.

What’s envisioned is a massive do-over of the highway and bridges that cross the Duckabush Estuary, a natural area of tidal wetlands of national significance. 

The project includes a new 1,600-foot-long elevated bridge across the estuary, along with wider shoulders along US 101 and a re-designed intersection at Duckabush Road.

Officials noted the Duckabush Estuary is currently impacted by fill, dikes, and road infrastructure that was built in the 1930s, which blocks water channels and limits critical habitat for fish and wildlife, including endangered salmon species.

The project would reconnect the Duckabush River to neighboring floodplains and wetlands by modifying local roads and elevating Highway 101 onto a bridge spanning the area where freshwater from the Duckabush River meets saltwater of Hood Canal.  

Officials stressed that the existing bridge, along with the fill and dikes that were put in place when the span was built, has blocked historic water channels and has reduced the habitat in the estuary. Removing the existing bridges and building a raised span across the estuary will benefit Hood Canal summer chum, as well as Mid-Hood Canal Chinook, two salmon species that are listed under the Endangered Species Act.

During the project update meeting Sept. 22, officials said completing the Duckabush River estuary would add to the Puget Sound-wide objective to restore river deltas and their wetlands.

The Duckabush Estuary project is eligible for federal restoration funding, said Theresa Mitchell, manager of the project for the Washington Department of Fish and Wildlife.

“Congress has created a limited time opportunity to direct federal funding to this location that supports broader Puget Sound recovery goals,” Mitchell said.

“There are feasible steps that can be taken here to improve the condition of the estuary,” she added.

The primary challenge to the estuary is the massive amount of dirt fill supporting the highway, Mitchell explained. 

“The placement of this fill, along with associated levees and other local roads, has locked the two main river channels in place to pass,” she said.

There are also six places where smaller channels have been completely blocked by the fill or forced into small culverts.

That’s completely changed where water flows and sediment moves in the estuary, Mitchell said, which impacts what type of vegetation can grow and how fish and wildlife use the habitat.

“The fill also creates a bathtub effect during high river flows,” she added.

Most people don’t notice the amount of fill that’s been used to create the highway crossing through the estuary.

“It is a bit hard to fully appreciate this impact because most of us experience the fill by driving on top of it on Highway 101,” she said. 

Tidal wetlands provide habitat for fish, shellfish, birds, and other wildlife, while also giving space for tidal and floodwaters to be absorbed.

State officials noted that more than half of Puget Sound’s historical wetlands in its 16 largest river deltas — roughly 57,823 acres – have disappeared due to development. That means less space for natural habitat for fish and other wildlife.

Officials noted the estuary project is a collaborative effort between Fish and Wildlife, the U.S. Army Corps of Engineers and the Hood Canal Salmon Enhancement Group, with support from the Washington State Department of Transportation.

Officials said removing the existing bridges and fill, and reestablishing the marsh under the new bridge, will mean greatly improved habitat for fish and other wildlife. And that’s important for the salmon population that relies on the estuary to survive. 

Removing the two old bridges, levee, and causeway would allow six historic channels of the Duckabush River to reconnect with other habitat areas of the estuary.

“Estuary habitat is considered extremely important for summertime salmon populations,” explained Mendy Harlow, executive director of the Hood Canal Salmon Enhancement Group. “And this is because salmon need to go through a physiological change when they go from freshwater to saltwater as juveniles, and from saltwater to freshwater as adults.”

“The mix of fresh and saltwater provides a good place to do that for both adults and juveniles. Estuaries are also important to juvenile salmon, because they need a high amount of edge habitat along riverbanks in order to avoid predation and forage for food,” she added. “More estuary channels means an increase of edge habitat to ensure their safety and their growth.”

The Duckabush Estuary is also important to salmon that are making their way out of Hood Canal from other watersheds further south, Harlow said.

The project also includes significant restoration efforts for the saltwater marsh along the highway. Large woody debris will be placed to improve habitat, and officials said any areas disturbed by construction will be replanted.

With the tidal channels reconnected, officials with the Corps of Engineers estimate that flood depths upstream of US 101 will be reduced during 100-year flood events.

Depths will be increased, however, at places where the levee and causeway for the existing bridges are removed.

A left turn lane from Highway 101 onto Duckabush Road is also in the project plans, along with additional public parking next to the wildlife area along Duckabush Road at the north end of the new bridge.

The new bridge will be roughly 6 feet higher than the existing span, which officials said would give greater room for high tides and flood conditions. 

Two existing culverts under US 101, and one under Shorewood Road, are also in the plans for the preliminary design. The new culverts would allow for better fish passage at both ends of the new 1,600-foot-long bridge. 

Officials said Duckabush Road would also be raised and realigned as it approaches the estuary bridge.

Plans for the new bridge include 12-foot-wide lanes, with shoulders 5 feet wide on both sides.

The Hood Canal Salmon Enhancement Group has been working with Fish and Wildlife to acquire land needed for the project, and has also done community outreach on estuary restoration efforts.

Harlow said property acquisition started in 2018 with the purchase of the old fire station building, and the enhancement group has coordinated the removal of the building from the land.

Earlier this year, the group acquired a parcel needed for the project near the highway’s intersection with Duckabush Road.

“We are currently in the process of acquiring the last major parcel for the project, which will bridge the gap between WDFW-owned parcels in the estuary,” Harlow added.

The preliminary design for the project was created by the Washington State Department of Transportation and the U.S. Army Corps of Engineers.

Design work on the project is expected to be finished by 2023.

Construction is estimated to take three to four years.

Preliminary plans predict some impacts to travelers during construction.

Officials said temporary signals will be installed and vehicles will be limited to one-way traffic.

Nighttime closures are also expected at Duckabush Road as the final tie-ins to the new bridge are finished.