Mike Stone, left, and Andy Sherman in the pumping station for Hannibal, Mo., during a flood in 1993. The city has since constructed a flood wall, and flood managers have built up levees to protect against flooding. But scientists warn those structures are making flooding worse.

Mike Stone, left, and Andy Sherman in the pumping station for Hannibal, Mo., during a flood in 1993. The city has since constructed a flood wall, and flood managers have built up levees to protect against flooding. But scientists warn those structures are making flooding worse.