Foiled Terror Plot

In a New York Daily News article titled Bomb tunnel, flood city I came across this:

The terrorists sought to drown the Financial District as New Orleans was by Hurricane Katrina, sources said. They also wanted to attack subways and other tunnels.

Naturally, I take all these kinds of things as seriously as they deserve. However, my question is this: Is it possible to flood New York? I haven't been there since 1975, so I don't really remember where anything is located. Even though this sort of thing would be devastating, in many areas, would it literally cause a flood in the city? I mean other than the obvious, the tunnels and subways.