Look up a graph of rising sea levels after the last glacial age. Writing starts precisely where the graph levels of to current levels.

After reading accounts of floods on the Mississippi before it was embanked and straightened. I'd totally believe that sort of stuff happened on the Tigris and Euphrates's rivers back 5000 years ago when it was wetter.

We can make it to the road in a homemade boat

That's the only thing we got left that'll float

It's already over all the wheat and the oats