I bought a block of land smack bang in the middle of a flood prone zone, quite clearly showing on the map it went under a number of times. Why did I buy it? because my further investigations uncovered that the developer had not only installed and widened existing water catchment areas as retention, but they had also elevated my block of land with fill by 10m. Not only that I witnessed two rain events where 600ml was dropped over a period of days & the next one over a period of hours, both times my lot was untouched.
Building in a flood prone area does not necessarily mean a no go zone, it just means you need to do further due diligence on the land.
Find out the problem areas in Brisbane or a specific address in order to plan for you building design or development and mitigate any unwanted costs down the track.