Earlier quoted context omitted.
What's wrong with below-ground power distribution for metropolitan areas?
I’m not an electrical or civil eng, but I imagine it’s very expensive to dig so many tunnels. Groundwater (especially for coastal cities) and people drilling holes would be very problematic too.
Power lines that are rated for conduit burial (which implies indefinite direct submersion in water is fine -- conduits leak, even if they're not supposed to) are readily available and not particularly expensive vs. above ground lines. Most of the cost is in the conductor, and that's the same either way.
If memory serves me right, you need to trench 6ft (which is usually done with a backhoe that has a narrow bucket and straddles the trench), then place a PVC pipe to act as conduit and fill the trench. The last step is using a (typically) pickup-truck mounted cable puller to pull the line through the conduit.
If the wire fails, you can pull it out and put a new one in without retrenching.
When you bury the conduit, you also bury a piece of warning cloth about one foot above it. If you see that while digging, then you should stop digging. (Also, call the "call before you dig" number before you dig.)
There are also trenchless systems that I've seen used for fiber optic cables. It's basically a tiny little boring machine (like they use to bore holes for tunnels) on the end of a cable. One person steers the boring machine, and the other stands above ground with a metal detector that tells them where it is, and how deep.