A river view is a priceless asset, or so the residents of Davenport, Iowa, believed. Now, however, they are realizing that their postcard vistas came at a price. Two weeks ago, the town, which had chosen not to build a levee, was swamped by millions of gallons of murky water. Yet while Davenport flooded, the business district of nearby Rock Island, Illinois, barely got its feet wet. Reason: in 1971 Rock Island decided to build a rock-and-clay floodwall.
In spite of the impression created by images of levees and houses being overrun by rising waters, the mounds of earth and rock...