A worker planting a new tree as part of the environmental mitigation work along the Blue Line.

Restoring and creating new wildlife habitat along East Link

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Although the Blue Line isn’t set to open until 2023, Sound Transit crews are already hard at work to offset the environmental impacts of East Link light rail construction.

When East Link goes into service as the Blue Line it will connect the Eastside to downtown Seattle with 10 new stations, including in Mercer Island, Bellevue and Redmond.

The alignment runs along Mercer Slough Nature Park, one of Bellevue’s largest parks and one of Lake Washington’s freshwater wetlands.

Wetlands are protected under the Clean Water Act, as are streams, ponds and lakes. When developments impact wetlands, they must be mitigated to ensure there is no net loss to the environment.

In honor of Earth Month, Sound Transit is celebrating the near completion of a six acre wetland rehabilitation and enhancement project at the Sweyolocken mitigation site, adjacent to the Mercer Slough and the future South Bellevue Station.

Planting crews walk through the Mercer Slough area being restored as part of the Blue Line construction project.
Crews walk the mitigation site near the Mercer Slough where wetlands are being restored as part of the Blue Line project.

Early work for long-lasting results

East Link has both both temporary and permanent impacts to these critical areas, but Sound Transit is following a new requirement for this project: that mitigation must start within a year of when the impacts begin.

“Sometimes mitigation comes at the end of a project. This was done early,” said Sound Transit Environmental Compliance Manager Marti Louther. “We’re trying to replace it as quickly as we can.”

Louther, a wetland biologist by training, led the project. It’s one of three mitigation sites in Bellevue, along with Coal Creek and the West Tributary of Kelsey Creek.

So far, 18,749 shrubs and 1,175 trees have been planted at Sweyolocken, in addition to 934 shrubs and 566 trees at Coal Creek and 6,529 shrubs and 222 trees at the west tributary of Kelsey Creek.

“We’re doing a lot of mitigation, and we always do more than what’s required,” she said. “We try really hard to be good stewards for our local resources and make them accessible to people so they can enjoy them. And part of it is to make it accessible to the wildlife, who really need it. We do a little bit more because we recognize the impact of past development, and the importance of maintaining what we have.”

Some of the native plants ready for their new home near the Mercer Slough.
Some of the native plants ready for their new home near the Mercer Slough.

After a detailed design and permitting process that involved local, state and federal agencies, work started about this time last year to restore the site. Bellevue has a deep agricultural history, and the Sweyolocken site used to be a private blueberry farm.

Sound Transit crews filled in two agricultural ditches to restore a more natural wetland hydrology, and removed invasive plants like reed canarygrass. Louther said the native system in the wetland is very robust and new native plants area already returning.

“When you remove invasives, you find some stuff that’s been repressed,” she said.

Sound Transit was mindful in reusing some of the trees in the area that had to be removed to make way for the light rail tracks.  

Much of the materials from the tree clearing operations was reused elsewhere, including for hundreds of habitat structures, like standing snags and log piles, built by Sound Transit for birds and animals to hide, shelter and forage in.

One of the stumps that will provide habitat in the expanded wetland area.
One of the stumps and root balls that will provide habitat in the expanded wetland area.

Things will change a lot at the site over the next few years. New plantings “sleep, creep then leap,” meaning that both the root and above ground growth will be in full swing about the time East Link opens in 2023.

“People riding light rail over the next 10, 20 years will watch the site progress, because it’s right next to the guideway when it starts to turn onto Bellevue Way,” Louther said.

And over time, the South Bellevue Station could become a destination for park visitors since it's right next door.

It includes the Mercer Slough Environmental Education Center, the Sweyolocken boat launch and seven miles of trails, along with another blueberry farm and the historic Winters House that will reopen after the Blue Line construction is finished.

In the meantime, you can see our work up close from the water. Launch your canoe or kayak at the Sweyolocken or Enatai Beach Park and head up the slough for a taste of wilderness wedged between two highways and the future Blue Line. 

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