People all over the world watched in shock and horror as they witnessed the devastation and destruction that Hurricane Katrina caused all over the New Orleans area. In retrospect, there will be lots of speculating about whether the damage would have been as extensive as it was had the situation with the levees been different. Most people don’t know or understand, why the New Orleans levees failed during Hurricane Katrina. If there is any hope of ensuring that the mistakes of Katrina will never be repeated, it is necessary to understand what went wrong, and why the levees failed.
• Storm surge shows weaknesses in levees –
When the storm surge came, force was added to the flow, thereby revealing weaknesses in the levee system. These weaknesses caused the breaches that compromised the entire levee system, flooding about 80% of the city of New Orleans. The answers as to why the levee system failed aren’t simple at all. Most of the levees along the 350 miles that they covered survived intact, even though levees were constructed to withstand nothing stronger than a category 3 storm.
Although Hurricane Katrina was classified as a category 3 storm, it was far different than any typical or previous category 3 storm, and it was the first failure of this magnitude. The Saffir-Simpson scale, as it was originally created in the 1970’s, was created as a way to warn the public of the impending storm and the risks associated with the storms. It was never intended to reflect the kind of damage that Katrina delivered.
• Misunderstanding the potential impact of Hurricane Katrina –
Hurricane Katrina was a slow moving storm with both massive amounts of rainfall and storm surge that far exceeded anything that was expected from the winds. All of these factors contributed to the monumental misunderstanding of what Katrina would do to the Gulf Coast. Although the misunderstanding was resolved in the scientific community just before the storm, there wasn’t any effort to communicate to the public, what was anticipated from Katrina quickly enough to facilitate a faster evacuation.
• Failures due to alterations in the original levee design –
The tragedy of New Orleans didn’t occur because of the over-topping of the levees, but rather because of the breaching. The breaching wasn’t the result of the levee design; it was directly related to the levee construction. The fact is, nearly all of the levees that were breached during Hurricane Katrina had been compromised long before the storm.
Levees were modified after their original construction in order to accommodate many other purposes. Some weren’t even constructed of the materials that met the original design specifications. The worst failure was an instance where a railroad track that was placed over the levee necessitated a compromise in the original design height of the levee. This allowed water to pass through porous gravel directly under the track.
Other failures might have been the result of other construction failures such as by filling the levees with a combination of materials that were originally specified and materials that were entirely sub-standard. The materials that were originally specified included clay like materials that were supposed to accommodate the space-conserving steepness of most typical urban levees. The sub-standard materials were local sandy soils or shell filled soils.
Because of those sub-standard soils, water was able to seep underneath the foundation of some levees as well the massive breaches or worse still, the explosive collapses of levees along Lake Pontchartrain and the Mississippi River Gulf Outlet (MRGO.) Ultimately, the failure was neither the result of engineering or substandard implementation.
• Failure in the levee construction –
By definition, a storm protection system must have redundancy. That redundancy must come either from strength (which is the safety factor,) or redundancy in the infrastructure (by having multiple levees that operate in tandem.) Neither of these types of redundancies existed in New Orleans, and in most cases, there was only a single levee standing between an uninhabited area and a waterway.
Although the U.S. Army Corps of Engineers has said that the levee system proper was designed to withstand category 3 storms, we know from history that multiple category 3 storms will hit that very part of the Gulf Coast during the course of a century. It therefore stands to reason, that the levees will fail once, if not more each century. We can then ask why the levee system didn’t have either sufficient strength or the parallel structures that are normally deemed mandatory, if not essential for a storm protection system.
Originally, the New Orleans levee system was designed for flood protection rather than storm protection. Naturally, this left the entire city vulnerable to the ravaging force of Hurricane Katrina. In the end, the fact that the original design of the levees was compromised so that the strength, structural integrity and infrastructure of the levees weren’t up to the standard that would be necessary to withstand the power of a hurricane like Katrina and the amount of rain that would be dumped on the city in so short a period of time all seemed to make the levee failure a catastrophe in the making.
Science Daily – New Orleans Levee Report Details: What Went Wrong And Why In Hurricane Katrina –
IEEE Spectrum: Flood or Hurricane Protection?: The New Orleans Levee System and Hurricane Katrina: Why was the New Orleans levee system so vulnerable to failure in Hurricane Katrina?
ASCE – Hurricane Katrina: Why did the levees fail?
USGS Scientists Investigate New Orleans Levees Broken by Hurricane Katrina –
New Orleans Hurricane Katrina Levee Failures –