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Between 80 and 90 percent of the residents of New Orleans were evacuated before the hurricane struck, testifying to some of the success of the evacuation measures. Despite this, not enough attention was paid to those without a car, credit cards, road experience or family living out of town. The Louisiana Superdome was used to house and support some of those who were unable to evacuate. Television shots frequently focused on the Superdome as a symbol of the flooding occurring in New Orleans.

The disaster had major implications for a large segment of the population, economy, and politics of the entire United States. It has prompted a Congressional review of the Army Corps of Engineers and the failure of portions of the federally built flood protection system which experts agree should have protected the city’s inhabitants from Katrina’s surge. Katrina has also stimulated significant research in the academic community into urban planning, real estate finance, and economic issues in the wake of a catastrophe.

Background

The original residents of New Orleans settled on the high ground along the Mississippi River. Later developments eventually extended to nearby Lake Pontchartrain, built upon fill to bring them above the average lake level. Navigable commercial waterways extended from the lake to downtown. After 1940, the state decided to close those waterways following the completion of a new Industrial Canal for waterborne commerce, which opened in 1923. Closure of the waterways resulted in a drastic lowering of the water table by the city's drainage system, causing some areas to settle by up to 8 feet (2 m) due to the compacting and desiccation of the underlying organic soils.

After the Great Mississippi Flood of 1927, United States Congress passed the Flood Control Act of 1928 which authorized the Corps of Engineers to design and construct flood control structures, along with levees, on the Mississippi River to protect populated areas from floods. It also affirmed the principle of local participation in federally funded projects but acknowledged that the $292 million already spent by local interests was sufficient to cover local participatory costs. It is instructive to note that, in addition, sovereign immunity was given to the Corps of Engineers under Section 3 of the Flood Control Act of 1928, which states “no liability of any kind would attach or rest upon the United States for any damage from or by floods or flood waters at any place, provided that if on any stretch of the banks of the Mississippi River it was impracticable to construct levees." 33 U.S.C. § 702c. Section 702c is sometimes referred as "Section 3 of the act," based on where it appears in the Public law.

Heavy flooding caused by Hurricane Betsy in 1965 brought concerns regarding flooding from hurricanes to the forefront. In response, the Congress passed the Flood Control Act of 1965 which mandated that henceforth, the Corps of Engineers is the agency responsible for design and construction of flood protection projects, to include those in Greater New Orleans. The local interests' role was maintenance once the projects were complete.

A 1999–2001 study, led by Richard Campanella of the Tulane School of Architecture, used LIDAR technology and found that 51% of the terrestrial surface of the contiguous urbanized portions of Orleans, Jefferson, and St. Bernard parishes lie at or above sea level, with the highest neighborhoods at 10–12 feet (3.0–3.7 m) above mean sea level. Forty-nine percent lies below sea level, in places to equivalent depths.

Also that year, Congress authorized the Lake Pontchartrain and Vicinity Hurricane Protection Project (LPVHPP) which reiterated the principle of local participation in federally funded projects. The project was initially estimated to take 13 years, but when Katrina struck in 2005, almost 40 years later, the project was only 60–90% complete with a revised projected completion date of 2015.

On August 29, 2005, flood walls and levees catastrophically failed throughout the metro area. Some collapsed well below design thresholds (17th Street and London Avenue Canals and also the northeast breach of the Industrial Canal). Others collapsed after a brief period of overtopping (southeast breach of the Industrial Canal) caused scouring or erosion of the earthen levee walls. In April 2007, the American Society of Civil Engineers issued its report and determined the flooding of New Orleans to be "the worst engineering catastrophe in US History."

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