Hurricane Katrina caused the levees surrounding New Orleans to fail due to poor design and the storm’s ferocity. The United States Army Corps of Engineers (USACE) admitted that the levees were only designed to protect from a category three storm due to restrictive funding. However, further investigations revealed that low-quality construction and poor design caused the levees to burst. USACE eventually admitted guilt in a series of Senate hearings. Early plans to replace the levees were of even lower quality than the original levees.
Anyone who has seen the media reports of August 2005 when Hurricane Katrina made landfall in New Orleans will remember images of water flooding the levees that were designed to protect the city. A number of factors caused the levees surrounding New Orleans to fail, ranging from poor design to the sheer ferocity of the storm, and these factors were considered when rebuilding the levee system in the storm’s wake. Other low-lying American cities have also considered the failure of levees in New Orleans when assessing their storm preparedness.
New Orleans is a city in a rather unique location, as it is entirely below sea level. Residents must contend with the surrounding Mississippi River, Lake Pontchartrain, and the Gulf of Mexico with a series of levees designed to keep floodwaters out of the city. When circumstances caused the levees to burst in the aftermath of Hurricane Katrina, the effect was similar to pouring tea into a saucer; water piled up with nowhere to go.
In the storm’s first 24 hours, 28 levees were broken, and the total level of broken or failed levees rose to over 50 within a week. The United States Army Corps of Engineers (USACE), which had built the levees, released an official explanation within days of the storm. According to USACE, the levees were only designed to protect New Orleans from a category three storm, and the storm surge generated by Hurricane Katrina was simply too massive for the levees to handle, which caused the levees to burst.
USACE officials justified the inadequate protection by explaining that funding for the levee project had been too restrictive for additional safety measures. The funding decision was based on a careful risk analysis, which weighed the potential for storms above category three against the cost of installing levees and the potential cost of dealing with the aftermath of a severe disaster. Risk assessment is often a gamble, and in the case of Hurricane Katrina, it would appear that the house won.
However, within weeks of the hurricane, more information about levee failures emerged, and professional engineering organizations speculated on several other scenarios that could have caused the levees to burst. One of the most significant pieces of information in these surveys was the debris line, which in many cases was below the level of the levee top. This means that the flood waters could not have overcome these levees, and therefore must have failed in some other way.
The engineers who criticized the levee failure pointed out that many of the levees were either poorly reinforced or built on substrates with low shear strength, which meant that when floodwaters pushed against the levees, they simply gave way. Additionally, sections of levees were often not interconnected, which would have increased their strength, and some of the levees were built on earthen or peat levees that had been severely eroded by floodwaters, causing them to break.
Independent studies concluded that low-quality construction and poor design caused the levees to burst. While USACE officials initially objected to this conclusion, they eventually did their own investigation and admitted guilt in a series of Senate hearings held to discuss Hurricane Katrina. Strangely, despite this lesson, early versions of the plans to replace the levees were of even lower quality than the original levees.
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