If your property meets the requirements for the federal flood insurance, you can buy it before the flooding happens.

Chuck, think I forgot to say I live in Manitoba Canada, what happens here?

With all the flooding that's going on, it seems like a good idea. I know that in each State it's a bit different. Try calling up your insurance rep and asking for premiums. Or indeed check how it is with the federal law. Hope no flooding will happen, though.