by Mondolithic Studios: Mondolithic Studios

By now you know that engineers had long predicted the cataclysmic flooding that struck New Orleans. But what you might not realize is that Katrina-a category-4 cyclone when it made landfall in Louisiana on August 29-was not the worst-case scenario. That would be a direct hit from a category-5 hurricane, which would send a storm surge over the city's levees and submerge New Orleans in minutes. Anyone who had ignored evacuation orders would drown.

New Orleans needs more protection than levees alone can offer. But in Louisiana, a comprehensive flood-control program had been repeatedly rebuffed-by environmentalists who fretted over the effects on ecosystems, by fishermen who feared for their livelihood, by engineers dead- locked over competing proposals, and by administra- tors who dismissed the plans as too expensive.

Katrina changed everything. All ideas-no matter how costly or far-fetched-are back on the table. In the end, officials might opt for a Band-Aid approach. They shouldn't. Relying solely on patched-up old levees is like asking the U.S. Border Patrol to fend off a full-scale military invasion.

Shielding New Orleans will require an arsenal of technologies that work collectively. We consulted experts from around the world to identify five innovative solutions that together could provide a category-5-strength de- fense. Although such a system would entail a ground-up reengineering of New Orleans and much of its nearby coastline, the payoff is a city more defensible against nature's wrath than any other. Here's our vision for safeguarding the city.