The New Orleans Hurricane Protection System: Assessing Pre-Katrina Vulnerability and Improving Mitigation and Preparedness (2009)

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1 Introduction I n the aftermath of Hurricane Katrina, the U.S. Army Corps of Engineers established the Interagency Performance Evaluation Task Force (IPET) to evaluate the performance of the New Orleans hurricane protection system (Figure 1) and to study the vulnerabilities posed to the city and the region by hurricanes. More specifically, the IPET defined the objectives of its study as: 1. the design and status of the hurricane protection system pre-Katrina; 2. storm surges and waves generated by Hurricane Katrina; 3. performance of the hurricane protection system during and after Katrina; 4. societal-related consequences of Katrina-related damage; and 5. risks to New Orleans and the region posed by future tropical storms. The IPET was established in August 2005 and over the next three years issued several technical reports. To provide independent review and advice to the IPET, the Assistant Secretary of the Army of Civil Works (ASA(CW)), Mr. John Paul Woodley, requested the National Academy of Engineering (NAE) to convene a committee of experts to review the IPET technical reports as they were being released. In late 2005, the NAE and the National Research Council (NRC) appointed a committee—the Committee on New Orleans Regional Hurricane Protection Projects—to review the IPET reports and issue independent, expert advice through a series of its own reports. The original plans for the IPET and its evaluations—which included plans to issue a final report in June 2006—changed course and evolved in many creative, useful, and challenging ways. Similarly, the original plans for this NAE/NRC committee—to issue three reports—followed these changes in the IPET schedule and evolved accordingly. During the course of this 3.5-year project, the committee convened seven meetings, five of which were held in New Orleans and two that were held in Washington, D.C. All meetings included presentations from IPET staff, the Corps of Engineers, and other invited experts; public comment sessions; and, closed sessions in which the committee discussed the IPET reports and its own draft reports. The IPET and Corps of Engineers provided an extensive amount of information to this committee in those meetings, which was essential to the committee’s education and to allowing it to provide informed feedback to the IPET. The professionalism and preparedness 8 

FIGURE 1 The New Orleans hurricane protection system. Map shows the features of storm surge damage in the New Orleans during and following Hurricane Katrina. Pink and blue shading indicates areas that flooded; blue-striped areas are wetlands. Starts indicate levee breaches or distressed levee areas; circles indicate pumping stations. 9 SOURCE: USGS. Available online at: http://soundwaves.usgs.gov/2006/01/NewOrleansMapLG.jpg 

10 The New Orleans Hurricane Protection System of the IPET and Corps of Engineers was of a high order and greatly facilitated the meeting discussions. Invited speakers provided informative presentations and perspectives that were invaluable to the committee’s work. The many citizens and representatives from New Orleans neighborhoods and businesses, and various city- and state-level groups, provided unique insights on technical issues and the context in which these issues were being applied. This NAE/NRC committee issued four reports from 2006-2008, which are summarized in Box 1-1. This following report is the committee’s fifth and final report. As directed in the committee’s statement of task (Appendix A), it represents a review of the IPET draft final report (dated June 1, 2008), and the committee’s reflections on the lessons learned from the Hurricane Katrina experience and ways in which the hurricane protection system performance might be improved. Over the course of the IPET project, many of the committee’s recommendations led to constructive improvements in the IPET reports. BOX 1-1 Previous Four Reports from the NAE/NRC Committee on New Orleans Regional Hurricane Protection Projects First report—February 2006 This report (NRC, 2006a) reviewed the IPET first report, which was issued in January 2006. It recommended that the IPET place a stronger emphasis on systems-level evaluation and presentation in many aspects of studies. It recommended that the IPET use more maps in its evaluations and findings, and that the IPET should make greater use of geographic information system (GIS) technology. The report included multiple recommendations for more thorough data gathering and testing of soil properties across the system. It also recommended that the IPET adopt an ensemble approach—reflecting a range of possible storms and storm surges—in its hurricane modeling exercises. The report also recommended that the IPET better characterize levels of confidence in the accuracy of the data that were being gathered and used in its various analyses. Second report—June 2006 This report (NRC, 2006b) reviewed the IPET second report, which was issued in March 2006. The report noted that although Task Force Guardian—the group responsible for repairs to the hurricane protection system—was making progress in repairing damaged structures, that the second report did not reflect well the remaining hydrologic risks to the system. It recommended that the concepts of authorized level of protection and standard project hurricane be better continued 

Introduction 11 BOX 1-1 Continued explained and integrated into the report, especially with regard to levee design. The report discussed the issues of potential failure mechanisms at levee breach sites, concluding that the explanation of the failure mechanism for the 17th Street Canal breach, while plausible, was not fully convincing, and that alternative failure mechanisms should be assessed. It recommended that special emphasis be given to gathering data at areas of the protection system that were loaded to near capacity by storm surges, but did not fail. It also was noted that the IPET faced a challenge in developing a robust and defensible assessment of the risk and reliability of the hurricane protection system, and it was recommended that IPET provide a thorough and understandable explanation for the method being used in its assessment of risk and reliability of the hurricane protection system. Third report—October 2006 This report (NRC, 2006c) reviewed the IPET draft final report, which was issued in June 2006. The report noted the prominence of risk and uncertainty within the IPET evaluations and reports, and recommended a stronger emphasis on explaining key uncertainties and implications for decision making. It recommended there be more substantial documentation to support the hypothesis that breaches along the Inner Harbor Navigation Canal (IHNC) were caused by overtopping and erosion, or foundation failure. It also recommended that the report examine other possible failure modes. Further advice on soils sampling and testing measures was included: it recommended that the IPET present site plans and soil profiles at breach sites, that clay and marsh deposit strengths be estimated at locations other than the 17th Street Canal, and that IPET provide additional guidance for identifying erodible soils, quantifying the degree of soil resistance to erosion, and selecting and placing soils to resist erosion. The report noted that although the IPET risk analysis approach was coherent and logical, that the levels of uncertainty in estimates of risks in flooding were expected to be large. It also recommended that as a complement to its joint probability methods results, that the IPET create a set of hurricane scenarios that simulate a variety of possible, future storm conditions for the New Orleans region. Fourth report—February 2008 This report (NRC, 2008a) reviewed a single volume of the IPET report— Draft Volume VIII on Engineering and Operational Risk and Reliability Analysis. That volume was released in October 2007. A key finding from this report was that the overall risk assessment method used by the IPET seemed appropriate for evaluating risks associated with the New Orleans hurricane protection system, but that the interim draft Volume VIII “does not provide sufficient presentation and explanation of the methods employed or results obtained to allow this to be clearly determined.” The report concluded that further information was necessary in order to fully explain and validate the method used and results that were obtained. The report recommended that the IPET more carefully document the data, assumptions, and models being used in its risk analysis, and that it present intermediate results and note that component models being used would evolve and improve over continued 

12 The New Orleans Hurricane Protection System BOX 1-1 Continued time. The report recommended that the IPET team/ discuss how the fragility curves of levee vulnerability could be improved through the use of more reliable shear strength measurements in either laboratory or field tests. It also recommended that the IPET issue a set of inundation maps that displays best estimates of inundation depths for 50-year, 100-year, and 500-year event recurrence intervals. The report further recommended that the modified joint probability model employed in Volume VIII be fully and clearly explained in a single place within the report, as opposed to partial explanations that were listed in multiple, separate sections. These reports are available at the National Academies Press website at: www.nap.edu/