The Gap is not prone to flooding, as khopki30 said but recently the creeks did creep up and there was water across the road on Waterworks Road. St. Johns Wood, just down from The Gap is more known for flooding.
It is a large suburb and for the majority of the suburb it is NOT a flood prone area. However there are creeks that run through the suburb that will flood and overflow if enough rain falls.
That said, the heavy rain over the Australia Day weekend caused a flooding issue the likes of which I have never seen. So I put some of the footage in a montage and posted on Youtube. Note that this house is on the side of a hill, not in a suspected flood zone.