What do you base that on? I may or may not agree with you depending on the numbers.
How much of the presently built up area is in a flood plain? Break down between residential and commercial/industrial.
If the flood plains were abandoned, what other space is available to build on?
100 year? 500 year? 5 year? I don't care if you build right on the beach, but don't expect the rest of us to help.There were a lot of places stupidly build in areas that flood and would not be allowed today. I know of an area in Tuckerton NJ that was built in the 1950's right on man made lagoons. Vacation homes, no heat, but right on the ground. Most have long been raised a few feet, some now year round houses that would. Codes have changed in those areas.
Never building in a flood prone area would make major differences in where we live and work. It would be interesting to see how it would affect us.
Disclosure: My last place of employment was right on a small river and we had 14" of water one time. Took us 3 days to get back in production and we did have flood insurance. Floods was easier to deal with than a fire. Did that ooo.