The answer lies in the levees themselves. Not the hurricane levees, but the river levees, the ones that hold back the great water of the Mississippi as it flows through New Orleans and the rest of south Louisiana. These huge earthen dikes have kept the city mostly dry from river floods for 300 years, thus making the town habitable. But the river levees also created the giant bathtub we all saw fill disastrously with water right after Katrina. And they've triggered the disappearance of one million acres of critical coastal wetlands and barrier islands in the last century alone that once protected New Orleans from storms like Katrina. Therefore, to protect New Orleans from future hurricanes we must do more than just build bigger levees. We must restore the battered coastal land between New Orleans and the Gulf of Mexico - and we must do it in a hurry.

A History of Lost Land

Every great river delta in the world is shaped by two unforgiving geological phenomena. The first involves flooding. The annual, repeated overflow of the sediment-rich Mississippi River is what created Louisiana's vast deltaic coast to begin with, depositing water-borne sediments and nutrients flowing down from two-thirds of America over the past 7,000 years.

The second major deltaic feature is "subsidence" or sinking. Those deposits of alluvial soil are extremely fine and unstable. Over time they compact, shrink in volume, and sink. Historically along the Louisiana Coast it was new flooding, new annual deposits of sediments, that counterbalanced the sinking and in fact led to net land building.

But by corseting the river with levees right out to the continental shelf of the Gulf of Mexico, we are left only with one half of the age-old equation: subsidence. The land just keeps sinking and sinking with no mitigation. Every day, even without hurricanes, 50 acres of land in coastal Louisiana turn to water. Every ten months, an area of land equal to Manhattan joins the Gulf of Mexico. It is, hands down, the fastest disappearing land mass on Earth.

This, fundamentally, is why Katrina happened. This is why people drowned and lost their homes and fled to refugee shelters or died of diabetic shock at the Superdome for lack of doctors.

When French colonists first settled Louisiana 300 years ago, there were vast tracts of dense hardwood forests between what is today New Orleans and the Gulf of Mexico. There were extensive fresh-water marshes and endless saltwater wetlands and a formidable network of strong barrier islands. Today, all that land is essentially gone. Because of the dikes and the "law of unintended consequences," New Orleans is a sunken, walled city essentially jutting out like an exposed chin toward the fast-approaching fist of the Gulf. Had Katrina struck two hundred or one hundred or even fifty years ago, the destruction would not have been the same. In 2005, there simply were no land structures left to slow Katrina's sledgehammer blow.

A Ray of Hope

The good news is there's a plan to recreate much of that lost coastal land between New Orleans and the Gulf. A detailed restoration scheme has been on the table since the 1990s to literally "re-engineer the coast." The plan is to build a dozen or so dam-like "control" structures right into the levees of the Mississippi River. These would then release the sediment-thick river water into canals or pipelines that would surgically direct the liquid soil toward the barrier islands and the buffering marshlands that need immediate restoration.

This so-called "Coast 2050" plan (visit www.crcl.org) will take many years to fully implement, but the cost is ridiculously cheap at $14 billion. That's just six weeks of spending in Iraq or the cost of the "Big Dig" tunnel-building project in downtown Boston. Yet tragically, even now, the Bush Administration has refused to fund this land-restoration plan so critical to New Orleans' future. Instead of $14 billion it has offered only $250 million, which is to say virtually nothing.

Given the horrors of Katrina and the prospect of another direct hit in the coming years, one can only hope the President will reassess his budgetary priorities. As a nation, our first responsibility is to assist the victims of Katrina who still lack housing and jobs. However, it would be criminally irresponsible of us to repair homes and levees in New Orleans without simultaneously committing - as a nation - to the massive plan to rebuild the Louisiana coastal wetlands and barrier islands. To do one without the other is to simply set the table for the next nightmare hurricane.