January 1, 2008
The levees and floodwalls protecting New Orleans from hurricanes and floods were designed to withstand a Saffir–Simpson category 3 hurricane (see US Army Corps of Engineers – USACE, 1984). When making landfall on 29 August 2005, Hurricane Katrina was designated a category 4 hurricane; later, it was downgraded to a severe category 3. The devastation that followed was more extensive than predicted by the USACE in 1984, but it was close to predictions made by scientists and emergency managers in more recent years (see Maestri, 2002; Laska, 2004). When examining the analyses conducted to support the 1984 decisions to fortify the levees and floodwalls, von Winterfeldt (2006, p. 31) concluded: In summary, there were several problems with the analyses and decisions regarding the development of levees and floodwalls in the New Orleans area: 1) probabilities and consequences of extreme hurricane events were underestimated; 2) alternatives that provided a higher level of protection were not explored; 3) the preferred alternative was implemented slowly and with many funding delays. Subsequent reports (for examples, Interagency Performance Evaluation Task Force – IPET, 2006; Seed et al., 2006) came to similar conclusions. More than a year later, the United States was again facing decisions about how to fortify and upgrade the flood protection system of New Orleans. In a previous paper (von Winterfeldt, 2006),we developed a simple decision tree analysis comparing two alternatives: rebuilding the levees and floodwalls to a 100-year flood protection level or building a new system that has a higher 1000-year protection level. Using a parametric analysis, the previous paper showed that a higher level of protection can be costeffective. The previous paper also described improvements to be implemented in a more complete and comprehensive analysis.