The centuries-old debt that's still paying interest

Right, for Miami, you might want kwelschermen (or a variant thereof: deep impermeable cutoff walls, doesn't need to be concrete, can be made by clay injection too) , californian style water injection, locks that reject salt water. Different place, different geology, different tools. No place is exactly the same. Thing is I figure you need some form of water board to manage it. A political entity that's all about "here we are and here we stay". Once they're set up they're pretty reliable (there's one that's still paying interest on a 370-year old bond ▶ this video )

These are rookie numbers! Tom Scott has a video about bonds that are being serviced continuously for more than 370 years: ▶ this video

Tom Scott has an excellent short video about just this topic if you're interested in further information about it. ▶ this video Quite an interesting video, definitely worth a watch!