Thursday, February 15, 2018

Fish window and Colman Dock construction

By Broch Bender

A fish window sounds like a great way to watch our gilled friends cruise through the water, but it's actually something a bit more important, and marks a significant milestone on our Colman Dock replacement project in Seattle.

You see, our crews can only do in-water construction work like pile-driving, from August to mid-February each year when migrating salmon are less likely to be around. Hence, the fish window. And that fish window closes on Feb. 15.
The fish window only allows in-water construction, such as driving steel piles to support the new dock, between August 1 and mid-February. We use a high power bubble machine in the water to minimize noise from pile driving.
That means that construction will still be happening on the project, but crews won't be driving support piles or doing any other work below the water line until August 1 when the window opens back up again.

The good news is, we've made great progress toward building a new terminal! During the last six months workers successfully installed 167 steel piles to support the future passenger-only dock and one-third of the trestle that will support a new ferry terminal building – all while protecting the environment.  A total of 500 steel piles are needed to make the busiest ferry terminal in the state safer in a major earthquake.
During the 2017-18 fish window, we installed steel piles to support the first part of the new main terminal
building, and the new King County Water Taxi and Kitsap Transit Fast Ferry location.

Keeping protected species safe
All in-water construction at Colman Dock temporarily stops when protected species, such as southern resident orcas or other marine mammals, are in sight. However, unlike our orca neighbors, migrating salmon can be tougher to detect beneath the surface of Elliott Bay. That's where the annual "fish window" comes in. Our biologists work with regulatory agencies to study salmon migration patterns and know when they are most likely to be in the area, and most likely not, and determine the window based on that information.

What's the big deal? What could happen to the salmon? Good question. The impact hammer used to drive in the last 10-15 feet of each steel pile creates underwater shockwaves that could cause them harm.

Though much quieter than pile driving, sediment capping is also done during the fish window, outside of the salmon migration period. Sediment capping carefully drops a layer of sand and gravel onto the bottom of the bay around the dock, to cap off hazardous materials that could threaten marine life. The impact of the sand and gravel hitting the bottom temporarily causes a hazy mix of sediment and saltwater, called turbidity, which could be difficult for fish to navigate. But once that settles down after a few minutes, fish and other species have a cleaner home.

We want to make sure everyone, from workers to wildlife, stay safe during the project.
The noise and vibration involved with installing steel support piles is disruptive
to marine mammals search for food and navigating through Puget Sound.

Upcoming construction at Colman Dock
Just because in-water work will pause doesn’t mean work will stop. Construction to rebuild the state’s largest ferry terminal is like a game of Tetris, fitting in work where it makes sense from the bottom up. Now that the fish window is closed, construction activity shifts to build the new terminal and passenger-only dock atop the steel pile foundation.

Starting in early March, crews will tear down sections of the  existing terminal building. Customers can expect full ferry service throughout construction, with no reduction in the number of sailings. However, there will be fewer amenities and public space while the terminal building is under construction through mid-2019.

Exterior demolition of the existing terminal building begins in late spring 2018, clearing the way to install new steel support piles on the north side of the dock once the next fish window opens this August.