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Residents wait on a roof top to be rescued from the floodwaters of Hurricane Katrina in New Orleans September 1, 2005. Authorities suspended an evacuation of New Orleans after a reported shooting at a U.S. military helicopter and President George W. Bush urged “zero tolerance” for lawlessness in the wake of Hurricane Katrina. Image Credit: Reuters

New Orleans: This city always had a different rhythm. It was the opposite of New York: After a stevedore was overheard saying, “If you can’t make it in the Big Easy, you can’t make it anywhere,” the phrase “The Big Easy” made its way from the African-American community into Newsweek, and spread. For decades, the city’s ambitious young men and women loved it yet fled, while those who did move here found places for themselves in existing spaces, slipping into its crevices, embracing it.

Hurricane Katrina, 10 years ago this month, changed much of that. The essence of the city — its rhythms and smells — survived the storm, even if it seems more like Disneyland than ever. But it has also become a dynamic place. After the storm, tens of thousands of volunteers flocked here to rebuild; thousands, many in their 20s, stayed. They did not seek to slip into existing space; they came determined to make, not find, spaces for themselves and to create a new American city.

Their energy — along with $71 billion (Dh260 billion) in federal spending in Louisiana, most of it in metro New Orleans — changed things. Amazingly to those familiar with the city, it is not only thriving, but also attracting talent. In 2014, Forbes put New Orleans at the top nationwide in growth in the number of college graduates, and in 2013, first as the destination where working-age Americans were moving. It has also become a leader in entrepreneurship, with what is now an annual Entrepreneur Week, which drew more than 10,000 attendees this year.

While poverty and crime remain, New Orleans now evinces a sense of possibilities unimaginable a decade ago. But there is one nagging question about the city’s future.

How safe is it?

That question relates not to crime, which is a serious but solvable problem. The question is whether the ocean will engulf the city — whether the city can continue to exist.

The answer is complicated, with important ramifications for other cities, including New York. New Orleans has a new flood-protection system, and unlike the pre-Katrina one, which failed because of mistakes made by the Army Corps of Engineers, the new system should perform as designed. It will protect against a so-called 100-year storm, the same protection New York seeks but does not yet have.

But there are three problems: the 100-year standard itself; geology and sea level rise; and politics. The first two may be solved. The last may be intractable.

“One-hundred-year protection” sounds safe but isn’t. It protects against a storm with a 1 per cent chance of striking in any given year, but during the average person’s lifetime, the odds that at least one storm will equal or surpass that standard exceed 50 per cent. The 100-year protection was originally supposed to serve only as an insurance standard, established in 1973 with the National Flood Insurance Program. It was never intended as a safety standard.

Indeed, before 1973, the Army Corps of Engineers built flood-protection systems to guard against the worst likely flood. That was the standard used in the 1930s when, after a 1927 Mississippi River flood more disastrous than Katrina, the corps built levees and floodways along the lower Mississippi River. That was fortunate, since floods also smashed the 100-year standard along the lower Mississippi in 1937, 1973 and 2011 but did little damage because of the levees and floodways. By contrast, areas of the country with levees built to the 100-year standard have been repeatedly devastated.

For New Orleans, which has always depended on the kindness of strangers, to feel smug about 100-year protection is foolish; for New York, with its immense value, to aim for 100-year protection is ludicrous. At landfall, Katrina had a 400-year storm surge; Sandy, depending on locality, had a 200- to 500-year surge.

The Netherlands protects cities against a 10,000-year storm; that is not affordable on the Gulf of Mexico and the East Coast, which face significantly stronger storms than the Dutch. But a standard higher than 100-year is. The minimum should be 500-year protection.

That is certainly attainable in New York, given its resources. Is it in New Orleans?

To answer that, one has to recognise that Louisiana’s entire coast was formed by the deposit of sediment carried by the Mississippi River. The sediment dropped out when it reached the ocean, first forming sandbars, and then as plants grew, firm land — 7,546 square miles of it, extending west to Texas. Humans have interfered with this natural process, and, since 1932, roughly 2,000 square miles, an area equal to Delaware, of Louisiana’s coast have disappeared. That land once provided a buffer absorbing storm surge.

Land loss is continuing at a rate that would dissolve an area the size of Manhattan in 18 months; if nothing is done, in the next 15 years, another 300 to 500 square miles of Louisiana will disappear — and loss will continue after that, turning New Orleans into a potential Atlantis with walls of levees holding back the sea.

Yet New Orleans does have a chance of surviving, for two reasons. First, it has adopted the concept — though it has done little to implement it — of “living with water,” for example, by raising houses. Second, and much more important, the same natural forces that created the coast could preserve enough of it to give Louisiana’s coastal areas a chance at a sustainable future. Little of what is gone can be rebuilt, and more land will still disappear, but even in the face of sea level rise, if given enough sediment and fresh water, land can be built in strategic places to protect populations.

In fact, New Orleans’ levee system is even now likely to protect against a 500-year storm’s “stillwater” height, the surge without waves. And waves dissipate over land, so rebuilding the land buffer can increase protection significantly. So the Mississippi River gives New Orleans and Louisiana a chance, arguably a better one than, say, Miami or Tampa or Houston, with cannot call upon the Mississippi for help.

Will it be done? The state has developed a “master plan” to do it. The biggest technical problem involves sediment, which has declined as much as 50 per cent, giving engineers less to work with than nature had. The state hopes to distribute the sediment through pipelines or “diversions,” which are openings in levees, to replicate natural flow.

But as difficult as the engineering is, the politics are more difficult. Most experts consider diversions the only long-term land-building option, yet oystermen have mounted a campaign against them, arguing that they will destroy oyster beds and fail to build land, while the shipping industry worries about any changes that could affect the channel.

And the fight over diversions is only a skirmish; the real fight will begin when people outside any planned protection realise their communities will disappear, or if the state adopts a proposal advanced by many experts to create a new river mouth, amputating part of the state. Already one region is angrily protesting a corps proposal that could require people to move from areas of “severe repetitive” flooding. Then of course comes the question of money. Officially, the statewide master plan will cost $50 billion. Approximately one-fifth of that would go to giving New Orleans 500-year protection. But a Tulane University study puts the actual cost for the master plan at more than $100 billion. And even at $50 billion, the state is woefully short.