For years, forecasters have warned of the nightmare scenario a big storm could bring to New Orleans, a bowl of a city that's up to 10 feet below sea level in spots and dependent on a network of levees, canals and pumps to keep dry. It's built between the half-mile-wide Mississippi River and Lake Pontchartrain, half the size of the state of Rhode Island.
Estimates have been made of tens of thousands of deaths from flooding that could overrun the levees and turn New Orleans into a 30-foot-deep toxic lake filled with chemicals and petroleum from refineries, and waste from ruined septic systems.