The Corps and industry also tore up the marsh by dredging hundreds of miles of channels so pipelines could be laid. Even bigger navigation channels were dug, and wave erosion from ships turned those cuts into gashes that allow hurricane-induced surges to race into the city. Similar practices are in play at many of the world's deltas, which could well benefit from plans such as those now being considered in Louisiana.

Too Late to Be Saved?
The 1998 plan for protecting the Mississippi Delta region, titled Coast 2050, and a modified scheme in 2003 known as the Louisiana Coastal Area plan (LCA), called for gates to be inserted into the river levees. The gates would open at certain times of the year to allow freshwater and sediment to wash down into the wetlands, gradually restoring them. But "a growing number of people are recognizing that Katrina and Rita changed the landscape enough that they may have made Coast 2050 and LCA obsolete," laments Len Bahr, a leader in the Louisiana Governor's Office of Coastal Activities for 15 years and an architect of Coast 2050.

Furthermore, because the storm surge entered New Orleans from Lake Pontchartrain to the north and navigation channels to the east, "those plans would not have stopped Katrina," observes Hassan S. Mashriqui, an assistant research professor at L.S.U.'s Hurricane Center who has enhanced the university's 1998 surge models. He says the models show that gates across certain channels into the city would also have been needed to divert the surge.

Those gates would have done nothing for the rest of southeastern Louisiana, however. Scientific American therefore asked a wide range of experts to present solutions for the region. Three strategies emerged: a tight ring around the New Orleans metropolitan area alone; a comprehensive, 440-mile levee system that would snake from the Mississippi border halfway to Texas but lie only partway to the shoreline, leaving the coast for lost; and an outer shield around the region's perimeter, such as the one in the Netherlands, which would spare every locale. The ring and comprehensive plans would inevitably leave some people "outside the wall." All three plans include gates of some kind that are not now in place.

Although each approach has its proponents, the parties agree on one thing: critics who say it is foolish to rebuild in such a vulnerable place are missing the big picture. In addition to being a cultural center, "the Gulf Coast is the economic engine that drives the country," Bahr declares. "We can't possibly abandon it." The delta produces one fifth of the country's oil, one quarter of its natural gas, and one third of its seafood. Trillions of dollars of goods and crops flow through the ports there. These activities require extensive infrastructure and tens of thousands of employees who cannot live in temporary trailers or in homes two hours away.

A New Path
Before any plan is implemented, designers should understand fully why the existing levees failed, so weaknesses can be avoided in the future. Four teams are investigating the levee and canal wall collapses in New Orleans--from the American Society of Civil Engineers, the Corps, the state of Louisiana and the National Science Foundation.

In October, Secretary of Defense Donald Rumsfeld announced that the National Academy of Sciences would review all the reports to ultimately determine why flood walls crumbled [see Working Knowledge, on page 92]. Rums¿feld said the academy would finish by June 2006. Yet hurricane season officially begins June 1, and Richard Wagonaar, a U.S. Army colonel and commander of the Corps' New Orleans district, says his goal is to restore all federal levees to their pre-Katrina level of protection (able to withstand Category 3 hurricanes) by that date. President Bush had asked Congress to appropriate $1.6 billion to repair levee damage from Katrina and in December requested another $1.5 billion to improve city levees at Category 3 levels.�

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