Mar 15, 2013
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New Orleans and Hurricane Katrina

This post continues our series on famous structural failures. More details can be found by taking a look at the seminars located on the “articles” page of www.AeroNavLabs.com

On August 29, 2005 hurricane Katrina, a category 3 storm, passed east of New Orleans. The storm had frequent intense gusts and storm surges. The storm caused 53 breaches in drainage and navigational canal levees. The Mississippi river & Lake Pontchartrain levees were also breached. The result was that over 80% of New Orleans was flooded and in some areas the depths were as high as 15 feet. Fortunately the French Quarter did not flood. The average elevation of the city is between 1 and 2 feet below sea level.

Floodwater Levels Following Hurricane Katrina. Source: www.loyno.edu

A map of New Orleans in 1900, if overlaid over a map showing the flooding in 2005, shows that the areas developed prior to 1900 did not experience extreme street flooding. The post 1900 areas had almost universal street flooding.  This is the result of the expansion of the city into low-lying areas.

Most of the levees were designed and built by the U.S. Army Corps of Engineers as part of the flood protection system for the city. The Corp has since testified that they followed “standard” handbook designs in building the protective systems for New Orleans.

The majority of the flooding was caused by the failures of the levees at three locations including the 17th Street canal. This canal breached an opening at least 50 yards in length. It breached with the water level 4 ft. below the design specifications. Soil borings that were subsequently taken showed a layer of peat between 5 and 20 ft. thick below the levees. The breaching allowed water from Lake Pontchartrain to flood large areas of the city, especially the Ninth Ward.

New Orleans has numerous emergency pumping stations. However due to the mass evacuations that were ordered, and the subsequent power failure, the pumping stations were inoperative. Pumping did not resume until 2-4 days after the storm. It is obvious that the flood protection system for New Orleans was an engineering failure of the highest order.

The following design factors contributed to the massive failure of the New Orleans flood protection system:

• Insufficient height of the levee walls
• Poor design of the levee walls with insufficient footings
• Insufficient depth of the wall foundations
• Poor subsoil conditions consisting of high proportions of low shear strength materials such as peat. Parts of New Orleans was built over formerly swampy areas as the city grew and expanded
• Using “standard” handbook designs where “non-standard” conditions prevailed
• Insufficient means were incorporated to prevent scouring of the soil beneath the levee foundations

The following steps have since been taken:

• Increased pumping capacity for the canals
• Make permanent repairs to storm-damaged levees
• Performed soil mechanics studies
• Purchased land adjacent to levees for future use
• Built additional levees (2012)

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