To the hurricane-battered residents of southern Louisiana, the Mississippi is more than a river, more than the mythologised waterway that splits the north American continent neatly in two. It is also a sinkhole that is slowly draining away their land, and with it their prospects of surviving another withering storm like Katrina.
Every year, the river carries 120 million tons of silt out of the bayous and lowlands to the south and east of New Orleans, and dumps it in the deep waters of the Gulf of Mexico. In other words, 120 million tons of land is simply scooped up by the Mississippi's murky waters and lost to the great north American land mass.
The delta region is losing land at the rate of a football field every half-hour or so. Or, to use alternative sporting imagery, the area of a tennis court every 13 seconds. This is not only a loss in and of itself. It is also stripping the big urban centres of Louisiana - New Orleans, primarily, but also the state capital of Baton Rouge, 80 miles further upriver - of a vital buffer from hurricane winds and ocean storm surges.
For years, environmentalists and some of the region's more far-sighted civil engineers have raged against the loss of Louisiana's coastal wetlands, and for years they have been ignored. Too much was riding on keeping the Mississippi delta just the way it was: the shipping companies who relied on certain waterways to gain access to the port of New Orleans, the energy companies who wanted to extract the oil from beneath the fragile surface of the land, and the property developers who thought about rising house prices and desirable water views long before they worried about the long-term viability of the terrain on which they planned one new subdivision after another.
That, though, was before Katrina caused New Orleans to flood. Coastal erosion was not a significant factor in last year's hurricane - the winds moved away to the east at the last moment, and the worst of the damage was done by the failure of the levees protecting the city from Lake Pontchartrain to the north - but it is becoming increasingly clear it could be crucial as and when the next big one hits.
It's no longer a question of pitting one interest group against another. Already in the wake of Katrina, some politicians questioned the wisdom of rebuilding New Orleans. A second storm of similar severity - or worse, since Katrina was only a Category 3 when it hit the Big Easy, having blown as strong as a Category 5 - could well deliver a death-blow to the city, and to the region. Who would want to live in a place whose weather patterns carry the stench of decay and death?
Desperate times call for radical solutions, and an intriguing one is being floated by a brand-new governmental body, the Coastal Protection and Restoration Authority. CPRA's proposal, which is finding a surprising degree of scientific unanimity, if not yet a solid outline with a dollar figure attached, is to shift the course of the lower Mississippi entirely. Instead of allowing the river to follow its current course, which takes it another 80 miles downstream from New Orleans to an artificial outcrop of land shaped like a bird foot, the idea would be to allow it to wash out into the Gulf sooner, where the millions of tons of silt it carries could come to rest in shallow waters. Over time, the bird foot peninsula would turn into a barrier island, while the new delta would develop into something of a natural land-reclamation project, building up the very wetlands that have been progressively lost over the past 80 years.
It's a dauntingly ambitious idea, one that could never have gained traction without a sense of crisis. But the crisis is unmistakably here, and the idea is taking off. "One of the major obstacles to doing any of this pre-Katrina was the navigation industry," James Tripp, an environmental lawyer and member of the state commission on coastal restoration, told The New York Times this week. "As a result of Katrina, everyone's thinking has become more flexible. Katrina brought all that home: how vulnerable this economic infrastructure has become... Is it practical? Yes. Will it be expensive? Yes. But when you look at the alternatives it's very cost effective."
In an era of global warming, shifting weather patterns, increasingly violent storms and rising tides, the outlook is less than rosy for a place like the Gulf coast, with its wide stretches of below sea-level marshland. The rate at which southern Louisiana is disappearing is believed to be the fastest instance of land erosion anywhere on the planet.
The notion of manipulating the course of the Mississippi is not as eccentric as it might at first sound. Human intervention has determined the direction of the river for the past century and a half, to the point where there is absolutely nothing natural about its current course at all.
If the Mississippi were allowed to flow freely - something some of the more radical environmentalists have been demanding for the past several decades - it wouldn't flow past New Orleans, and the vast port and petrochemical industries there, at all. It wouldn't even cut through Baton Rouge. It would take a more directly southerly course from a point near Lettsworth, about 250 miles inland, and seep down the Atchafalaya River to Atchafalaya Bay 100 miles west of New Orleans.
The reason it doesn't is because of the system of concrete levees built up along the river bank for much of its progress through southern Louisiana. The levees were originally designed, starting in the 19th century, as flood protection. Over time, though, they have interfered with the river's natural rhythm of "switching", which is to say, changing direction according to long-term silt deposit patterns.
It is impossible, in fact, to divorce the course of the Mississippi with the history of human settlement and development in the region. Lousiana's legacy of slavery provided the first levee builders with a ready pool of low-wage black workers who made the anti-flooding barriers cost-effective for the landed classes. During one bad flood in 1913, blacks were used as human sandbags to protect the assets and property of their white overlords. In the great Mississippi flood of 1927, the fathers of New Orleans chose to dynamite some of the levees north of the city to save themselves from inundation. The fact that poorer rural areas were devastated by the rushing waters that jumped the Mississippi's banks was not something that bothered them unduly.
The 1927 disaster marked the beginning of federal government intervention in regional flood control, including the more robust system of levees carrying the Mississippi along its current course. At the time, scientists saw a straight trade-off between land preservation and flood prevention: Louisiana could have one or the other, but not both, and flood prevention became the priority. The wetlands have been receding at their alarming rate ever since.
The industrialisation of the region only added further layers of complication. Shipping channels, most notably the Mississippi River Gulf Outlet (known locally as Mr Go), have kept the region's economy humming, but they also provide an entry way for storm surges and flooding from the Gulf.
Oil, gas and the petrochemical industry have also wreaked damage that is only now being seriously discussed. The network of canals and pipelines the energy sector has created has in turn triggered severe marsh erosion and collapse. The celebrated journalist A J Liebling noticed the damage being wrought by oil extraction more than half a century ago, memorably writing that Louisiana "floats on oil like a drunkard's teeth on whiskey". And it's only got worse since.
Oliver Houck, an environmental law professor at Tulane University in New Orleans and another prominent coastal restoration activist, told a local newspaper recently that state politicians were to blame for their "slavish defence" of the oil and gas industry.
"Over 10,000 miles of canals are now eroding and the marshes are caving in," he said, "and somebody big is walking away from the table."
Even without another hurricane, the erosion patterns are deeply disturbing. Within the next 50 years, shallow water is going to be lapping all the way up to the New Orleans city limits. And that's an optimistic scenario. A less optimistic scenario, according to Randy Hanchey of Lousiana's Department of Natural Resources, is that the city will actually be on the Gulf Coast by mid-century. One storm surge, and, like the resort communities in Mississippi a few dozen miles to the east destroyed by Katrina, the whole place could be wiped off the map.
This week, Mr Hanchey told The New York Times: "A major diversion in the lower part of the river is something that needs to be done." In practical terms, that would probably involve opening the levees 45-55 miles south-east of New Orleans. To accommodate shipping, the scientists are thinking of creating a slack-water channel - a protected entrance way to the Mississippi controlled by a gate or system of locks. Residents of a handful of small towns in the bird-foot peninsula would have be relocated, but the population there is negligible.
There would be land compensation issues and land rights issues, all of which are likely to be complicated. There would also be the question of whether the scheme - costly and complicated as it would be - would really work. Nobody would want to spend the next 15 years carrying out a river diversion scheme only to discover it caused more harm than it repaired.
Mr Hanchey told the Times: "Our ability to understand and model river responses to actions like this has improved. The technology of hydrodynamic modelling has improved, and of course we have tremendously increased computational power we did not have before. We can run models today in a matter of hours that took weeks even 20 years ago. All of that has improved.
"Still, whether we can model the river precisely I don't know. It's going to require a lot of data. It's going to require a lot of brains."Reuse content