On ancient Susquehanna, flooding's a frequent fact

Early settlers called the Susquehanna River "a mile wide and a foot deep." It's just a folk saying, but it hints at the forces behind a river that is, in fact, exceptionally likely to flood.

And flooding it is, with record or near-record levels recorded along its path from New York state to Chesapeake Bay after a wet summer that included storms Irene and now Lee.

"The Susquehanna is one of the most flood-prone rivers in America," said Chris Duffy, a professor of civil and environmental engineering at Penn State University.

It's an especially shallow river, Duffy said, and that means big rainfalls can create floods rapidly. But another issue is what's underneath the water....