If you dig tunnels under an island a few feet above sea level.
At least have the sense to put storm gates on all of the openings to prepare for the storms that have historically flooded the island.
Most of the NYC tunnels had no storm doors. The few subway stations that did have doors failed because they were built more for aesthetics than functionality.
People will understand if you tell them the truth.
The hurricane barrier at the entrance to New Bedford MA harbor is ugly to look at everyday, but it works the once every 30 years it has been needed.