2005 levee failures in Greater New Orleans

On Monday, August 29, 2005, there were over 50 failures of the levees and flood walls protecting New Orleans, Louisiana, and its suburbs following passage of Hurricane Katrina. The failures caused flooding in 80% of New Orleans and all of St. Bernard Parish. In New Orleans alone, 134,000 housing units — 70% of all occupied units — suffered damage from Hurricane Katrina and the subsequent flooding.^[1]

When Katrina's storm surge arrived, the hurricane protection system, authorized by Congress forty years earlier, was between 60–90% complete.^[2] Responsibility for the design and construction of the levee system belongs to the United States Army Corps of Engineers, while responsibility for maintenance belongs to the local levee districts. Six major investigations were conducted by civil engineers and other experts in an attempt to identify the underlying reasons for the failure of the federal flood protection system. All concurred that the primary cause of the flooding was inadequate design and construction by the Army Corps of Engineers.^[3] In April 2007, the American Society of Civil Engineers termed the flooding of New Orleans as "the worst engineering catastrophe in US History."^[4]

On January 4, 2023, the National Hurricane Center (NHC) updated the Katrina fatality data based on Rappaport (2014). The new toll reduced the number by about one quarter from an estimated 1,833 to 1,392.^[5] The Rappaport analysis wrote that the 2005 storm “…stands apart not just for the enormity of the losses, but for the ways in which most of the deaths occurred.”^[6] The same NHC report also revised the total damage estimate keeping Hurricane Katrina as the costliest storm ever––$190 billion according to NOAA’s National Centers for Environmental Information.^[7]

There were six major breaches in the city of New Orleans itself (the Orleans parish, as compared to Greater New Orleans which comprises eight parishes):

1. Three major breaches occurred on the Inner Harbor Navigation Canal (locally known as the Industrial Canal). A breach on the northeast side near the junction with the Gulf Intracoastal Waterway flooded New Orleans East. Two breaches on the southeast side between Florida Avenue and Claiborne Avenue combined into a single 1,000 foot wide hole that allowed stormwater to catastrophically rush into the adjacent Lower Ninth Ward.
2. On the western edge of New Orleans near Hammond Highway, a breach opened in the 17th Street Canal levee. Floodwater flowed through a hole that became 450 feet wide, flooding the adjacent Lakeview neighborhood.^[8]
3. The London Avenue Canal in the Gentilly region, breached on both sides; on the west side near Robert E. Lee Boulevard and on the east near Mirabeau Avenue.

Storm surge caused breaches in 20 places on the Mississippi River-Gulf Outlet Canal ("MR-GO") in Saint Bernard Parish, flooding the entire parish and the East Bank of Plaquemines Parish.