Amsterdam also sits on porous (in theory) sand. Compacted sand lets only little water through though and that is pumped out. Bigger problem with his argument is

Amsterdam also sits on porous (in theory) sand. Compacted sand lets only little water through though and that is pumped out. Bigger problem with his argument is that Amsterdam is lot more like London or Philadelphia than Miami - it's not really at the sea. There was an inlet Zuiderzee that was dammed, just like river Thames or Delaware river could be (expensive but probably doable). Miami is surrounded by sea