Modern day New Orleans was a city that defied the odds. Built on a mosquito-infested swamp surrounded by water, it sits in a bowl 2.5m below sea-level. Its very existence seemed proof of the triumph of engineering over nature.
But on the 29 August 2005 the city took a direct hit from Hurricane Katrina and overnight turned into a Venice from hell. In the chaos that followed the worst natural disaster in American history, a forensic investigation has begun to find out what went wrong and why. Scientists are now confronting the real possibility that New Orleans may be the first of many cities to face extinction.
Professor Ivor Van Heerden of Louisiana State University’s Hurricane Centre used computer modelling to simulate hurricane paths across New Orleans. He had been appointed by the state to discover why New Orleans flooded so catastrophically and had his own unique methods of gathering data. By collecting eye-witness testimonies from residents and the stopped clocks from their flooded homes, Van Heerden pieced together a timeline of the levee breaches. He also took samples from the breach sites for analysis.
His results were shocking. He believed they showed that there was a design fault in the levees. “The old system that led to the design and the building of them, the funding, the decision making process, didn’t work. We’ve got to change that and part of that is going to be for the federal government and the engineers corps to step up to the plate and say we screwed up.”
Over the years the levees and dams stopped annual floods from the Mississippi River. As a result sediments that were brought down by the river to replenish the land were prevented from reaching their natural destination. Gradually Louisiana started to lose its coast. Today it has the highest rate of coastal land loss in North America. Every 20 minutes an area the size of Wembley stadium is swallowed up by the sea.
Shea Penland, a coastal geologist at the University of New Orleans, knows every inlet, every cove and every stretch of marsh that surrounds the city. He also knows that Louisiana’s wetlands, thought of as wasteland for years, are in fact critical to the survival of the city. Providing protection against storm surges, these wetlands are a natural defence against the onslaught of hurricanes. As he says: “The first line of defence isn’t the levee in your backyard, the first line of defence is that marsh in your back yard and we’re learning what that means.”
After the disaster, he chartered a seaplane to investigate the overnight loss to Louisiana’s precious wetlands. What he discovered sounded like the death knoll for the city. In just one night, Louisiana had lost three-quarters of the wetland that it usually loses in one year. Without this protection, New Orleans is a sitting duck against future storms.
And the problems don’t just stop there. The city itself is sinking. Since 1878 it has dropped by 4.5m, one of the highest rates of subsidence in the entire United States. Once again it’s mainly human intervention that is to blame. According to Professor Harry Roberts, a geologist at the Louisiana State University: “It’s been accelerated by man’s efforts to keep the water out of the city. When you pump the water out of those kinds of soils they start to collapse and even more importantly the organic material oxidises and goes away so you’ve taken out one component of the soil, and all that adds up to subsidence.”