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Those who've spent years planning a transformation of Seattle's waterfront closely watched the final leg of Bertha's journey and celebrated when the tunnel boring machine finished digging on Tuesday morning.

Seattle Mayor Ed Murray called Bertha's breakthrough a "major construction milestone" in the plan to reclaim the city's waterfront.

The folks with Waterfront Seattle had a similar message, describing Bertha's big finish as a "major historic milestone" that will bring the city one step closer to removing the Alaskan Way Viaduct and transforming the waterfront area.

That's because the bulk of the waterfront makeover can't happen until the viaduct comes down. And of course, the viaduct can't come down until the new tunnel opens to traffic. That's why Bertha's breakthrough is such a big deal for the waterfront area.

"It is huge," said Heidi Hughes, executive director of Friends of Waterfront Seattle. "This is a moment for the city that we're all so excited and proud of because we've been getting ready for this moment for years. Six years of public input; 10,000 public comments - all about what the future waterfront can be to serve all citizens of Seattle and become this common gathering space."

Friends of Waterfront Seattle is the non-profit that was established to partner with the city on the waterfront project. The organization's goal is to ensure the project's legacy as a beloved park.

"Think about having 26 blocks from Pioneer Square to Belltown with something like the Olympic Sculpture Park in the middle," said Hughes. "You remember when you could go to concerts on the piers, when you could come to the waterfront to hear great music? We want to do that and more with 26 blocks of programmable public space. You can come and listen to music, play soccer, have a fun day with your family, all without spending a dollar."

But again, all of that hinges on the removal of the Alaskan Way Viaduct, now slated for 2019.

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Waterfront business owners said they too were rooting for Bertha to finish.

"We can now hopefully look forward to the tunnel being completed so we can change the waterfront and the feel of it, and maybe create some more excitement down here," said Jennifer Martin, who works at the newly opened Seattle Shop at Pier 56. "I think when the viaduct is gone it will open this area up and make it a more beautiful place to come and visit."

A project overview from Waterfront Seattle describes the rebuilt Elliott Bay Seawall, along with 20 acres of new public space, improved connections between center city neighborhoods, and new Alaskan Way and Elliott Way surface streets to serve all modes of travel.

"We will build a waterfront for pedestrians, transit, and sensible car trips without a freeway wall casting a shadow over our vision of a well-connected 21st-century city," said Murray.

So what's the next big milestone for the waterfront project?
"Completion of the seawall, we're almost there," said Hughes. "Then the new Pike Place Market front in June, followed by Pier 62's rebuild and re-opening in 2019."
The viaduct will be demolished once the new tunnel opens to traffic in 2019. At that point, construction of the new waterfront park will really kick into high gear.
"So it's a series of milestones. There's going to be a lot happening down here in the next few years, and we're ecstatic," said Hughes.

Photos: What will Seattle's waterfront look like when the tunnel's completed?