Dams that take longer than 10-12 turns should basically never be hard-built, since almost certainly it's going to be better to build it using engineers. And generally speaking, by the time Dams become available, they are already roughly even in cost with the Engineer costs, not even counting discounts you can get on engineers. I mean, it rarely gets this far, but my current game passed the -50% gold buy on units and I was suzerain of Ngarzagamu, so by that point, my ME could be bought for like 85 gold apiece in my cities. So in that case, yeah, it's definitely worth the dams.
But overall, yeah, builder costs are pretty marginal for flooding. and honestly, half the time a river floods, it adds +1 food back to the tiles, so if all I'm doing is farming the river, I'd almost rather not have my floods be mitigated. Where the cost matters more are the turns to repair a district that was placed on a floodplain. 3-4 turns lost on a big IZ or campus or even a couple turns lost when a commerce hub floods can be pretty annoying to repair back.
But overall, yeah, builder costs are pretty marginal for flooding. and honestly, half the time a river floods, it adds +1 food back to the tiles, so if all I'm doing is farming the river, I'd almost rather not have my floods be mitigated. Where the cost matters more are the turns to repair a district that was placed on a floodplain. 3-4 turns lost on a big IZ or campus or even a couple turns lost when a commerce hub floods can be pretty annoying to repair back.
