Eli5 – How do you build a dam?

Question

The recent dam collapse had me thinking how on earth do you build a dam? Huge river with loads of water – how do you even start without the water washing everything away? How do the workers manage to cope in such conditions?

In: 21

Answer 1

Typical is to go upstream from the desired dam location, and make a diversion around the area. Then build a simple dam (fairly small) called a coffer dam to force the river to flow through the diversion. This dries and exposes the final dam site for construction.