I keep a flotation vest as part of my kit, for crossing water obstacles and for flooding. I live on the third floor, though I'm only a block from the river, I should be good if for some reason I don't leave in time.
I think some type of boat or a floating platform would be a good idea. One of my stories had a guy build his deck next to, but not attached to the house. It was built with the big float chambers that they build floating docks with underneath. There were four guide posts, one at each corner. Steel rings fastened to the deck went around the posts to guide it upward without it floating away if it began to flood.
The story was based on something my father did that was similar. He not only kept a boat tied up at the back door of the house, his radio shack and hang out building was built with flotation just like the deck in the story. We lived between the Mississippi and St. Francis rivers in the bootheel of Missouri and could get floods any given summer.
Definitely want to get a PFD for everyone. Might want to invest in a canoe or jon boat, or an inflatable. Personally I want to get one of these for both floods and for water crossings when bugging out. https://www.alpackaraft.com/index.cfm?fuseaction=store.catalog&categoryID=53&ProductID=87
Just some ideas.