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Every other Friday, the Outside/In team answers a listener question about the natural world. Got a question of your own? The Outside/In team is here to answer your questions. Call 844-GO-OTTER to leave us a message.

Outside/Inbox: How do we build things underwater?

Pile casing for a bridge foundation
Pile casing for a bridge foundation

Every other Friday, the Outside/In team answers a listener question about the natural world. This week’s question comes from Todd in Buffalo, N.Y.

He asks: “I work on a boat in Lake Erie, and we have a water intake facility that takes in hundreds of millions of gallons of water a day…through a 12-foot wide pipe. And I just don’t understand how they built that. If you could help me out, how do we build things underwater?”

Outside/In’s Felix Poon and Nate Hegyi looked into it, and here’s what they learned.


This has been edited for length and clarity.

Felix Poon: What are your thoughts, how do you think they build things underwater?

Nate Hegyi: I think that they build it outside of the water, and then I guess they probably have divers that lead it down, and then the divers just smash it into wherever it needs to go.

Felix Poon: That’s not a bad guess. But I spoke to Justin Alves. Justin’s a pile driver and he builds offshore wind turbines. In fact he was at work on a ship just off the coast of Halifax, Canada when I called him.

Nate Hegyi: Oh cool!

Felix Poon: And Justin says diving is part of some types of underwater construction. But that’s not the case for most projects, and probably not with this underwater pipe either.

Justin Alves: I would imagine they built a cofferdam. You would barrier that off, and you would be able to do your work in that area.

Nate Hegyi: Barrier it off, like they would create a dam where it moves the water away?

Felix Poon: Yeah, pretty much. Humans have been using cofferdams for literally thousands of years. They could be as simple as building walls out of dirt, if it’s a shallow project. But for deeper projects they use different materials, like these tall sheets of steel that get pounded down into the ground underwater, and linked together, kind of like Legos. Once the area is totally sectioned off and the water’s drained out, then they get to work.

So that’s probably how this pipe got put in under Lake Erie. But the work Justin’s doing, he’s building support structures for things like piers and wharves, bridges, and offshore wind turbines. And these foundations are made from piles, basically these giant poles or tubes made of steel or concrete that go deep into the ground. The ones used for wind turbines are called monopiles.

Justin Alves: They start with the monopile. They put that in the ground, hammer it in the ground, and then they put what's called the transition piece on top of that.

Felix Poon: I mean these things are basically manufactured on shore, and then they bring them out on these barges and the barges have these giant massive cranes.

Justin Alves: The capacity of this crane for the vessel that I'm on is 5000 tons.

Nate Hegyi: Wow!

Felix Poon: Justin’s job as a pile driver is actually a lot of rigging – like, tying and hooking up monopiles – so then the crane picks it up, puts it in the water, puts it in place, and then a big hydraulic hammer keeps hitting the top again and again, thousands of times, driving it down into the ocean floor.

Nate Hegyi: So there’s no divers or anything else like that? Like, is he ever diving?

Felix Poon: Yeah no. They don’t need to do that because they have robots with cameras to see underwater.

Justin Alves: They use what's called “ROV,” which is “remote operated vehicles.” They kind of just navigate with controls. Honestly it's like playing a video game for these guys.

Nate Hegyi: I should’ve thought about drones, the fact that they have these underwater drone robots to do all the work of divers these days.

Felix Poon: Yeah, exactly.

Nate Hegyi: A lot safer.

Submit your question about the natural world to the Outside/In team. You can record it as a voice memo on your smartphone and send it to or call the hotline, 1-844-GO-OTTER.

Outside/In is a podcast! Subscribe wherever you get yours.

Felix Poon first came to NHPR in 2020 as an intern, producing episodes for Outside/In, Civics 101, and The Second Greatest Show on Earth. He went to work for Gimlet Media’s How to Save a Planet before returning in 2021 as a producer for Outside/In. Felix’s Outside/In episode Ginkgo Love was featured on Spotify's Best Podcasts of 2020.
Outside/In is a show where curiosity and the natural world collide. Click here for podcast episodes and more.
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