You just dig around the water.

Make a hole somewhere else, pick it up on a crane, drop it into the water. Job done.

Amusingly close to the truth.

The sides are made elsewhere, and craned in. They are then pile-driven into the riverbed. You can then pump the new hole dry, and start working on the foundations.
No Just put sand on the parameter until it reaches the surface then use sponges to dry out the water inside
- Just use a straw doofus

Just bucket the water source block, duh

It's all source blocks, we're gonna need to spam sponges

But like… how did they even do the first step of ramming the wood piles into a deep ass river without big machinery of some kind?
- Long time and unlimited resources is usually the way to go. Sure machinery would make it fast, but you can get 10 guys to hammer for 2 years to drive it. Then move on. Even today it's a huge logistics and financial problem to build bridges which is why typically it's always governments that did it.
- The machine that shows up about 3 seconds in looks to me like a manual piledriver, uses pulleys and cranks yo pull the weight up, then just gravity to drop it down the track.
- Sledgehammers (or similar) and lots and lots of manpower I'd guess. It's how they made it watertight before they drained it I'm interested in
- The oldest way to do it is to start from a bank and work your way in section by section.
  
  It's a cofferdam if anyone is interested.
- Aliens

Step 1: Cut a hole in the water

Moses, that you?

This thread is just like reddit threads. All quips and one liners and minimal actual conversation, these posters are indistinguishable from karma-farming bots.

Literally all but 1 top level comment at the time I posted this one.

Why is the quality so damn low? It's honestly depressing, part of the reason for leaving reddit was to get away from what is essentially auto-generated drivel/spam to actually interact with other humans interested in interacting with other humans.

This is done by pounding metal pilons & sheets into the riverbed side-by-side to create a semi-sealed off section surrounding the work site This can be done in two layers, an outer and an inner wall, and the gap filled with soil. Then the water is pumped out and workers can effectively work in the now exposed riverbed.

Sir, this is a c/humor
What meaningful conversation did you want from a post that shows a hole in a large body of water? XD
If I wanted to know how bridges work, I wouldn't be in c/humor.
Isn't lemmy.world supposed to be reddit but not reddit? Honestly this is kind of expected.
- Well it's supposed to be Reddit for the tankies. Only they've mostly gone over to lemmygrad now, but there's still enough wingnuts hanging around to remind us of them.
...and yet half the posts are memes, unlike Reddit.