It isnt a question of local tides it is a question of how a tide can overtake you on a sand flat. When the sand is just wet it is like firm ground, as soon as the water reaches your level it is impossible to walk on, you just sink in it. A sand flat is nominally completely flat and smooth so when the sea level rises by a foot you are a mile from firm ground, that is what those poor Chinese and you dont and didnt understand, and that is the point I just made. You understand the theory, you actually just proved you dont understand what it means.