Well I was once a HK resident so I was kinda mad that they'd sunk my native home.
Anyways, here is a bit of geography lesson. Hong Kong is made up of 2 large islands and a peninsula (ignore the remaining small islands) From what I can tell, it was only the Hong Kong Island that went submerge, while the Kowloon Peninsula and the Lantau Island remain surfaced ...
Episode 14 really solve a lot of mysteries.