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Observations

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Protecting New Orleans five years after Hurricane Katrina

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louisiana-flood-barrierThis Sunday, August 29, is the fifth anniversary of the day Hurricane Katrina inundated New Orleans, which touched off one of the most egregious and most publicized tragedies in modern American history. Scientific American published an article in 2001 that predicted precisely the kind of destruction the storm wrought, based on computer models of hurricane paths and storm surges. Unfortunately, politicians and engineers responsible for flood protection did not listen to the scientists who were running the models. After 1,400 people died in the wake of Katrina and the nation’s pitiful emergency response, Louisiana and the federal government convened several independent panels of scientists and engineers to propose ways to better protect New Orleans and the entire Mississippi Delta from future hurricanes.


The initial plans that emerged did not necessarily agree, so Scientific American sat a subset of the experts in a room and asked them to hammer out the most promising options, which we published in February 2006. After several years of delay, the U.S. Army Corps of Engineers, which is essentially chartered by Congress to protect the nation from floods, began building the first new structures intended to keep floodwaters out of New Orleans, which the media has been covering this week. High walls are being erected around certain parts of the city, old levees that had collapsed under the pressure of high water are being raised and strengthened, and gates have been built across some of the open canals and navigation channels that allowed the Katrina storm surge to topple those levees. The Corps has released a map and an animated video of the plan.


Interestingly, the plan looks a lot like the first of three options we described and diagrammed in our 2006 article


"Scientific American 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.


Residents in the hurricane danger zones hope that whoever gets the job incorporates new understanding of how Katrina and Rita ravaged New Orleans, and some worry that the Corps may not be fully responsive to external scientific information. For example, Hassan Mashriqui at Louisiana State University has determined that a wide breach in the Industrial Canal, which flooded the eastern section of the city after Katrina, was caused by what is called a funnel effect. Computer simulations, and physical evidence Mashriqui obtained in October as a member of the state inspection team, show that Katrina pushed water from the east up a wide navigation channel called MRGO and simultaneously up an adjacent channel, the Intracoastal Waterway. The two wave fronts met where the inlets join and narrow into the Industrial Canal. This geometry amplified the height of the water by 20 to 40 percent, Mashriqui says. That increase raised the water pressure so high that the canal wall burst."


It seems the Corps has listened this time, because the linchpin of the system now under construction is a 1.8-mile wall that has been built across the funnel area, separating the Intracoastal Waterway and the Industrial Canal from surges that would come in from the Gulf of Mexico. It has also installed gates across several of the canals that would stop a surge that entered into Lake Ponchartrain, on the northern edge of the city, from flowing down into city streets.


The Corps’ plan looks a lot like the “tight ring” around the city that was recommended in our 2006 article. The work is schedule to be finished in 2011 and is estimated to cost $15 billion. This approach still leaves the rest of the delta south of the city vulnerable—to hurricanes, as well as to oil that might wash ashore because of, say, an oil spill in the gulf. The vast but rapidly disappearing wetland regions are vital to fishing, shrimping and oyster farming, migratory birds and even pipelines that head to offshore oil platforms. Whether these areas will ever be protected by expanded strategies remains to be seen.

Image: Courtesy of U.S. Army Corps of Engineers

The views expressed are those of the author and are not necessarily those of Scientific American.

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