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What Caused the Levees to Break in New Orleans During Hurricane Katrina?

Mary McMahon
Updated May 17, 2024
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Anyone who watched media reports from August 2005, when Hurricane Katrina made landfall in New Orleans, will remember the images of water flooding over the levees which 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 wake of the storm. Other low-lying American cities also considered the failure of the levees in New Orleans when evaluating their own preparedness for storms.

New Orleans is a city in a rather unique position, because it is entirely below sea level. Residents must contend with the surrounding Mississippi River, Lake Pontchartrain, and Gulf of Mexico with a series of levees which are designed to keep floodwaters out of the city. When circumstances caused the levees to break in the wake of Hurricane Katrina, the effect was akin to slopping tea into a saucer; the water pooled with nowhere to go.

Within the first 24 hours of the storm, 28 levees had failed, 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, issued 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 break.

USACE officials justified the inadequate protection by explaining that the funding for the levee project had been too restrictive for additional safety measures. The funding decision was made on the basis of careful risk analysis, which weighed the potential for storms above Category Three against the cost of installing levees, and the potential cost of coping with the after-effects of a major 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, additional information about the levee failures emerged, and professional engineering organizations posited several other scenarios which could have caused the levees to break. One of the most significant pieces of information in these investigations was the debris line, which was below the level of the top of the levee in many cases. This means that the floodwaters could not have topped these levees, and therefore they must have failed in some other way.

Engineers who criticized the levee failure pointed out that many of the levees were poorly reinforced, or built on substrata with a low shear strength, which meant that when floodwaters pushed against the levees, they simply gave way. In addition, the levee sections were often not interlocked, which would have increased their strength, and some of the levees were built over dirt or peat levees which were severely eroded by the floodwaters, causing those levees to break.

Independent studies concluded that low-quality construction and poor design caused the levees to break. While USACE officials initially resisted this conclusion, they ultimately carried out their own investigations, and admitted culpability in a series of Senate hearings held to discuss Hurricane Katrina. Oddly enough, 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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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a America Explained researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments
By amypollick — On Feb 05, 2012

All these comments are completely spot on. One huge shortcoming was the governor not ordering contraflow on Interstate 59 and Interstate 10 out of the city. Seeing as how Mississippi, Alabama and Texas were threatened as well, I know the governors of those states would have been more than happy to cooperate with Louisiana in getting contraflow through their states. I-59 should have been northbound only, from New Orleans, at least to the Mississippi state line, and probably to Meridian, Miss. Interstate 10 should have been eastbound only from New Orleans east to Mobile, Alabama and westbound only to the Texas state line. This would have facilitated getting people out of town much more quickly.

Part of what caused the levees to fail is also the unnecessary volume of water behind them. This was a direct result of the city of New Orleans draining nearby salt marshes and building strip malls, etc., on them. Salt marshes hold a tremendous amount of water and kept New Orleans from flooding during historic hurricanes like Audrey and Betsy.

The "laissez les bontemps roulez" attitude of the Big Easy may be part of its allure, but that attitude from city and state government officials nearly destroyed their historic city.

As a point of comparison: in 2004, when Hurricane Ivan barreled into the Alabama Gulf Coast, the governor ordered northbound contraflow on I-65 to Montgomery (about 170 miles), and the mayor of Mobile ordered mandatory evacuations about 60 hours before landfall. Preparedness is everything. Ivan was a strong Cat 3 storm, and we managed to get our people out. We also took in a lot of Katrina refugees. We're 8 hours from New Orleans. The national media can say what they want, but we know what really went down when Katrina hit. We have friends and family who lived through it.

By sneakers41 — On Sep 19, 2010

Sunshine31-I actually would be afraid to live in a city that is not only built below sea level, but is surrounded by water.

I know many people live there and love it, but the image of Katrina and what could happen in the worse case scenario would not make be want to live there.

I could understand why the residents stayed away. People need to feel secure and I think that this experience really made people understand the risks of living in such a community that is below sea level and surrounded by water.

My heart broke for the people of New Orleans and I am glad that many moved on to other areas and started new lives.

By sunshine31 — On Sep 19, 2010

Moldova-I heard that the cost was something like 100 million dollars to reinforce the levees to this level. That does seem like a lot of money.

But there is so much corruption in Louisiana politics that if many of its career politicians would have been serious about helping the city of New Orleans, they would have made this a priority long ago.

At least, Governor Bobby Jindal did a fantastic job in evacuating residents of New Orleans when they had another potential hurricane scare.

The hurricane did not hit New Orleans, but it was in the cone area which was enough for the Governor to act. This is the type of action that should have take place during Katrina.

By Moldova — On Sep 19, 2010

Mutsy- The problem also is that businesses say that they will return when the residents return and vice versa.

After five years the population is still dismal and does not look like it will get better. With few employment prospects and substandard living conditions it is no wonder that most people looked elsewhere to rebuild their lives.

Also, business owners not only have to worry about the lack of potential customers, but the exorbitant insurance rates and the possibility that this very thing could happen again.

The hurricane Katrina levees were repaired but in order to prevent this catastrophe from happening again, the Army Corp of Engineers would have to build the natural levee to sustain a hurricane 5 status which gusts the strongest winds and storm surge.

By mutsy — On Sep 19, 2010

Sunny27-I think the aftermath of Katrina really made people take notice of this city.

Since so many businesses left as a result of the storm, residents have no home or job and had to relocate to other locales.

This really made part of New Orleans look like a ghost town. To this day, the lower 9th Ward, the hardest hit area from the Katrina hurricane, is about 80% vacant.

There are accounts that many of the homes are still dilapidated and the area is infested with rats and snakes. In addition, the crime rate is still quite high. In fact, New Orleans has one of the highest rates of murder in the whole country.

By Sunny27 — On Sep 19, 2010

Hurricane Katrina really illustrated the problem that can occur to a city that is built below sea level.

The New Orlean levees breaking combined with the lack of an action plan by the city and state government really added to the catastrophe.

Mayor Ray Nagin did not have an emergency plan in place and told the residents to leave when it was too late. He had tons of school buses that could have taken residents out of the area easily.

Instead the buses remained empty in the city and over $1,000 residents died. The Governor was also clueless and did not take any aggressive action.

The state and local government blamed the Federal government, which also has some faults in the matter, but the majority of the blame needed to be placed on the local authorities, after all it is their city.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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