The three gorges dam was recently built; and closer to SV, Site C is under construction in British Columbia. There's definitely folks alive who know how to build dams.
I think the issue is less the lack of knowledge, and more the lack of political will to meaningfully tackle the problem.
Capital spending and construction are far more friendly to electoral politics than ongoing maintenance and operating expenditures.
People see what a good job you've done getting a dam built or a bridge constructed, they vote for you. People don't vote for you because they didn't suffer the consequences of reduced maintenance. People vote against you if you raise taxes to pay for maintenance or if they're inconvenienced by shutdowns while they repair your dam or bridge.
I'm currently on a project in California to repair and rehab a dam to extend its service life, working for a contractor that just finished a dam rehab job and is bidding on two more in the future.
The work is being done, probably not at a scale or pace big enough to meet the needs of the infrastructure (see: all those old and ailing bridges across the country) but it is being done at some level.
The problem is you need to burn alot of dead trees to make a dam and EROEI is dwindling too fast for this to become a viable option. Nuclear and hydro will never be rebuilt to the same level we have now.
If anything nuclear's problem is even more political than practical.
We could fulfill the world's nuclear waste storage needs with a couple landfills if the will was there (though any geologist will tell you are better options than near surface storage).
From an ecological perspective nuclear is the best option by a mile because the amount of stuff you need to pull out of the ground, move around, use and dispose of is so small per energy produced.
Nuclear has 1.000.000.000x the energy density of batteries so yes, but you need dead trees to build and maintain power lines, the power grid cannot be remade after it's current decline.
Tiny local hydro (with natural dam) is the future, but getting a building permit is near impossible. (I leave it to the reader to guess why)
We need to switch off electricity for everything except (low power) computers and networks. = hand pumped water, wood stove for water heater, earth cellar as fridge!
Mass transports are completely over, grow/breed/preserve your food locally!
Even ignoring the CO2 aspect, the particulate emissions from this would be quite problematic in any sort of dense area. Not to mention what fraction of those particulates would end up inside the house...
Also, you don't mention heating (houses, not water). That is a huge part of energy consumption in many parts of the world.
> Site C is under construction in British Columbia.
Not sure if this is a good example of "know how to build dams". It's a dam foolish design, built on an earthquake fault zone that's been made unstable by the excavation that's being done to build the dam. The design has been changed to include this ridiculous earthfill section (https://www.sitecproject.com/about-site-c/site-c-project-com...) to compensate for the weirdness of the geography there. It's probably going to fail catastrophically at some point and destroy a lot of homes downstream from it, and the controversy over the project basically caused the downfall of BC's last government.
My friend does some auxiliary work for Site C. He said everything is over budget and a mess. The initial contractor underbid because they thought they could get migrant workers in. But now they are dealing with union workers so the contractors messed it up badly.
I think the issue is less the lack of knowledge, and more the lack of political will to meaningfully tackle the problem.