The Idea behind this is to transition old buildings that are located at the coast or rivers, that regularly flood or are going to get permanently flooded, into new water safe buildings.
Yes a dike or dam is cheaper but buildings don't last forever, so why not prepare new ones and transition old ones to be future-proof.

Not sure if this is possible but it's an idea that can be worked with. Using the water pressure to anchor a building in the ground.

Using the water pressure to anchor a building in the ground. Version 1.2. I've decided to rework this. The first one was just too goofy.