page_title: Hurricane Katrina
section_title: Analysis of New Orleans levee failures
hierarchical_section_title: Hurricane Katrina / Aftermath / Analysis of New Orleans levee failures
caption_attribution_description: English: View of the eyewall of w:Hurricane Katrina taken on August 28, 2005, as seen from NOAA WP-3D Orion hurricane hunter aircraft before the storm made landfall on the United States Gulf Coast. Français&#160;: Vue de l'œil de l'ouragan Katrina photographié le 28 août 2005 à partir d'un avion de reconnaissance de la NOAA avant que le cyclone n'atteignît la côte américaine. Español: Vista de la pared del ojo del huracán Katrina tomada el 28 de agosto 2005, visto desde un avión de NOAA Orión WP-3D cazador de huracanes, antes de que la tormenta tocara tierra en las costas del golfo de Estados Unidos.
context_page_description: Hurricane Katrina was a large Category 5 Atlantic hurricane which caused over 1,800 deaths and $125 billion in damage in August 2005, particularly in the city of New Orleans and the surrounding areas. It was at the time the costliest tropical cyclone on record, and is now tied with 2017's Hurricane Harvey. The storm was the twelfth tropical cyclone, the fifth hurricane, and the third major hurricane of the 2005 Atlantic hurricane season, as well as the fourth-most intense Atlantic hurricane on record to make landfall in the contiguous United States.
  Katrina originated on August 23, 2005 as a tropical depression from the merger of a tropical wave and the remnants of Tropical Depression Ten. Early the following day, the depression intensified into a tropical storm as it headed generally westward toward Florida, strengthening into a hurricane two hours before making landfall at Hallandale Beach on August 25. After briefly weakening to tropical storm strength over southern Florida, Katrina emerged into the Gulf of Mexico on August 26 and began to rapidly intensify.
context_section_description: According to a modeling exercise conducted by the U.S. Army Corps of Engineers (USACE), two-thirds of the deaths in Greater New Orleans were due to levee and flood wall failure. On April 5, 2006, months after independent investigators had demonstrated that levee failures were not caused by natural forces beyond intended design strength, Lieutenant General Carl Strock, Chief of Engineers and Commander of the Corps of Engineers, testified before the United States Senate Subcommittee on Energy and Water that "We have now concluded we had problems with the design of the structure."
  A June 2007 report released by the American Society of Civil Engineers determined that the failures of the levees and flood walls in New Orleans were found to be primarily the result of system design and construction flaws. The U.S. Army Corps of Engineers had been federally mandated in the Flood Control Act of 1965 with responsibility for the conception, design, and construction of the region's flood-control system. All of the major studies in the aftermath of Katrina concluded that the USACE was responsible for the failure of the levees. This was primarily attributed to a decision to use shorter steel sheet pilings during construction in an effort to save money. According to a report published in August 2015 in the official journal of the World Water Council, the Corps misinterpreted the results of a 1985 study and wrongly concluded that sheet piles in the flood walls needed to be driven to depths of only 17 feet (5 m) instead of between 31 and 46 feet (9 and 14 m). That decision saved approximately US$100 million, but significantly reduced overall engineering reliability.
  In January 2008, Judge Stanwood Duval of the U.S. District Court ruled that despite the Corps' role in the flooding, the agency could not be held financially liable because of sovereign immunity in the Flood Control Act of 1928. Exactly ten years after Katrina, J. David Rogers, lead author of a new report in the official journal of the World Water Council, concluded that the flooding during Katrina "could have been prevented had the corps retained an external review board to double-check its flood-wall designs."
  Other factors may have contributed to the flooding. According to the authors of Catastrophe in the Making (Island Press, 2009), the straight design and lack of outward flow into the Gulf allowed the Mississippi River-Gulf Outlet Canal to become "the perfect shortcut for salt-water intrusion" which damaged buffering cypress forests and wetlands which historically had protected New Orleans from storm surge. The Army Corps of Engineers built and maintained the canal. Furthermore, according to storm surge researcher Hassan Mashriqui:
  Storm surge pushing across shallow Lake Borgne from the east is constrained by these MRGO levees to the south and, to the north, by the long-standing levees of the Intracoastal Waterway (GIWW). Initially ten or more miles apart, these two channels meet, and when they do, the water building between their levees is squeezed into a single channel – the Funnel – only 260 yards wide, constrained by levees 14 feet to 16 feet high….In concert with the denuded marshes, it could increase the local storm surge hitting the Intracoastal Waterway by 20 percent to 40 percent – a critical and fundamental flaw.
  The Corps of Engineers disputes these causalities. Nonetheless, in June 2008, the Army Corps of Engineers New Orleans District submitted a Deep-Draft De-authorization Study of the MRGO which stated that "an economic evaluation of channel navigation use does not demonstrate a Federal interest in continued operation and maintenance of the channel." Congress ordered the MRGO closed as a direct result.
  Many of the levees have been reconstructed since Katrina. In reconstructing them, precautions were taken to bring the levees up to modern building code standards and to ensure their safety. For example, in every situation possible, the Corps of Engineers replaced I-walls with T-walls, which have a horizontal concrete base that protects against soil erosion u
caption: View of the eyewall of Hurricane Katrina taken on August 28, 2005, as seen from a NOAA WP-3D hurricane hunter aircraft before the storm made landfall on the United States Gulf Coast
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