If finished by 2011 as planned and supported by an effective stormwater pumping system, the $14.3-billion hurricane and storm-damage risk-reduction system of levees, gates and floodwalls going up around New Orleans will “dramatically reduce” vulnerability to flooding and potential loss of lives and property during extreme storms events, according to a new report that explains the extraordinary risk-analysis tools developed to study the system since Hurricane Katrina’s devastation in 2005.
“If it’s constructed and performs equal to what we assume it will in the model, it’s going to be a hell of a system,” says Lewis “Ed” Link, the director of the project that produced the analysis.
The 2011 system is scaled to defend against a storm flood of a severity with a 1% chance of occurring in any given year, usually referred to as a 100-year storm. According to the analysis, the 350-mile-long system of levees and facilities should resist breaches and overtopping, limiting water within the defenses to rainfall. If pumps perform at even half of nameplate capacity, the defenses should reduce the probability of loss of life from flooding by 97% and direct property damage by 93%, relative to the conditions seen during Katrina.
Those conclusions and more are spelled out in a 61-page “Supplementary Report,” designed to synopsize for a general audience a far larger body of work. The synopsis is one of three documents released on June 26 as the Interagency Performance Evaluation Taskforce finished more than 44 months of effort.
IPET was commissioned by the chief of the U.S. Army Corps of Engineers on Oct. 10, 2005, to analyze causes and consequences of Hurricane Katrina’s Aug. 29, 2005, destruction in New Orleans and guide engineers rebuilding flood defenses. The wrap-up follows final peer reviews of the supplement, a 288-page executive summary and a 224-page Volume VIII, which explains how engineering and operational risk and reliability analysis was done. There are nine volumes in all.
Link says the projected reduction in vulnerability after the 2011 project is complete is encouraging, but the larger value of the analysis establishes a reliable methodology and benchmarks for evaluating risk mitigation achieved and gains anticipated from policy changes and physical improvements in the future.
“It is a really important strategic look at the situation,” says Link. “It shows you not only where you have the biggest problems, but why and what’s the source of the vulnerability.”
The reports explore many other projection scenarios that were run to evaluate the residual risk prospects for the city, including the state of defense in 2007, after initial repairs were made, and other storm events of various intensities.
The IPET work has been praised by the The National Academy of Engineering’s committee on New Orleans regional hurricane protection projects, one of its peer reviewers, for “groundbreaking work, intellectual energy and the professional dedication.” But the committee pushed the IPET team to finish and publish, particularly the probability and risk volume, as soon as possible and in forms thoroughly supported by explanatory documentation. It also wanted a separate form that could be understood by nonprofessionals. These final publications respond to those recommendations.
“Ed Link and the IPET team were very responsive to our suggestions,” says G. Wayne Clough, chair of the National Academy committee. “The chapter they worked on longest, on risk and reliability, was really groundbreaking. While that approach had been used for earthquake issues and dams, it had not been used for levees and hurricanes, which is a different kettle of fish. One of the big contributions they are leaving behind is a whole approach to dealing with the risk and probability issues with levees and hurricanes.”
The reports can be downloaded at https://IPET.wes.army.mil.