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The New Orleans Hurricane Protection System: Assessing Pre-Katrina Vulnerability and Improving Mitigation and Preparedness 2 The IPET Draft Final Report The collective IPET evaluation entailed large, important human resources and institutional efforts and investments. Numerous individuals and organizations devoted extensive amounts of time and energy into this multi-year, multi-agency project. In addition to the IPET studies and reports, the Corps of Engineers and the Department of the Army sponsored two multi-year external reviews of the IPET study process and its reports, which were conducted by the American Society of Civil Engineers (ASCE, sponsored by the Corps) and by this NAE/NRC committee (sponsored by the Department of the Army). The analytical, computational, presentation, public communication and relations, logistical, and other related challenges to the IPET were substantial. Adequate assessment of the five IPET study objectives required an ambitious and extensive research program, which is described in eight volumes of over 7,500 pages of report chapters and appendices. In addition to its evaluations of the design and performance of the New Orleans HPS during Hurricane Katrina, and its evaluations of Katrina’s waves, surges, and impacts, knowledge gained in answering these questions: 1) was applied directly to the design and construction of immediate and longer term repairs, 2) was used to assess the integrity of and plan remedial actions for the sections of the HPS not severely damaged, 3) is being used in the ongoing efforts to enhance the capabilities of the system to achieve 100-year levels of protection, and 4) provides analytical methods and a body of knowledge to assist in planning and designing more effective protection measures in the future (IPET, 2008, p. I-1). The IPET represented an unusual study for the Corps of Engineers (and others) in that they brought some of the best scientists and engineers in the world to work together with Corps engineers and scientists toward a set of goals. The IPET project has improved greatly the understanding and management of the New Orleans regional hurricane protection system (HPS). The IPET draft final report of 2008, however, cannot be regarded as fully conclusive or as “the final word” with respect to all study objectives. That is, the size and the complexity of the natural and human systems involved in hurricane protection,
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The New Orleans Hurricane Protection System: Assessing Pre-Katrina Vulnerability and Improving Mitigation and Preparedness preparedness, and forecasting for New Orleans is such that many parts of the IPET studies never could be “final.” Hurricane protection is an ongoing, work in progress to which the IPET has made noteworthy contributions that serve as a platform for future inquiry and for the development of research priorities. The remainder of this chapter presents the committee’s observations and comments about the IPET draft final report and is organized according to the five IPET study objectives. CHARACTERIZATION OF THE PRE-KATRINA HURRICANE PROTECTION SYSTEM The IPET evaluations and reports in this area advanced greatly the understanding of the pre-Katrina state of system and its vulnerabilities. Volume I explains, for instance, that the hurricane protection system “…did not perform as a system” (IPET, 2008). In discussing the administrative and organizational history of the HPS, the IPET draft final report makes it clear that the “system” was constructed in a piecemeal fashion, “in many separate steps over a long period of time” and represented a history of “continuous incompleteness” (Ibid., p. 31). Details on this region’s geologic setting also explain widespread subsidence and how this affected levee heights, stability, and reliability. The IPET report also explains how the system was incomplete in some areas, that there were different vulnerabilities across the region, and that parts of the system were unreliable and had been inadequately designed. These types of evaluations were overdue for this region; unfortunately, it took a disaster on the scale of Hurricane Katrina to provide the impetus for this kind of study. This explanation of the pre-existing condition of the HPS marks one of the important contributions of the IPET studies and will be essential information for future hurricane planning and construction activities in the region. EVALUATION OF HURRICANE KATRINA STORM SURGE AND WAVES The IPET work in this area represents an important advance of scientific understanding of Gulf of Mexico hurricane storm surge and waves. The IPET did a good job of explaining the storm surge generated by Hurricane Katrina, how waters from the surge entered into the New Orleans metro region from the east and from the north (across Lake Borgne, into Lake Pontchartrain, and ultimately into the city’s outfall canals and the Inner Harbor Navigation Canal), the role of the Mississippi River Gulf Outlet in exacerbating storm surge (minor, if any), and inundation depths across the city. The IPET work also importantly identified the significance that the areal extent of Katrina played in determining
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The New Orleans Hurricane Protection System: Assessing Pre-Katrina Vulnerability and Improving Mitigation and Preparedness storm surge; it was primarily Katrina’s large size that contributed to the highest storm surge ever measured in North America. The IPET also implemented and calibrated state-of-the-art models for coastal wave and storm surge response. PERFORMANCE OF THE HURRICANE PROTECTION SYSTEM DURING AND AFTER KATRINA The IPET conducted a detailed evaluation in this area and provided explanations of the HPS performance during Hurricane Katrina. As explained in the Executive Summary of the draft final report, IPET concluded, “With the exception of four foundation design failures, all of the major breaches were caused by overtopping and subsequent erosion” (IPET, 2008, p. I-2). The report further states that “The levee-floodwall designs for the 17th Street Canal and London Avenue Outfall Canals and the IHNC were inadequate for the complex and challenging environment.” In a September 3, 2008, letter to Corps of Engineers Chief Robert van Antwerp, the American Society of Civil Engineers (ASCE) External Review Panel complimented the Corps for its acknowledgement that designs were inadequate for extreme hurricane conditions, but also noted that “engineers routinely are expected to design for such conditions” (ASCE, 2008). This report concurs with the ASCE team on this issue. The nature of the performance of the hurricane protection system during Hurricane Katrina was an important area of investigation in the IPET studies, especially the geotechnical assessments of the four sites of foundation failures in the HPS. Special explorations were conducted in the field, which were complemented by laboratory centrifuge studies and analytical investigations using numerical modeling and limit analysis. The IPET team concluded that a singular driving mechanism was a key factor affecting each of the failures; however, alternative factors contributing to failure were proposed by others, notably by a research team that was working through a grant from the National Science Foundation (NSF). An earlier report from this NAE/NRC committee drew attention to the complex soil conditions and the number of unknowns still associated with these sites despite the extensive work conducted (NRC, 2006b). In the end, that report advised the IPET to “be aware of alternative failure mechanism and assess the potential for instability at other locations along the levee system” and that “The explanation of the failure mechanism for the 17th Canal Street breach, while plausible, is not fully convincing, and alternative failure mechanisms should be more rigorously assessed” (NRC, 2006b). These issues likely will continue to be debated, with a gradual professional consensus developing about appropriate means to incorporate these findings into future design. For the time being, all reasonable possible failure modes in designs for levees and floodwalls should be considered and examined, and attention should be given to ongoing professional discussion about the issues in order to facilitate design improvements.
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The New Orleans Hurricane Protection System: Assessing Pre-Katrina Vulnerability and Improving Mitigation and Preparedness SOCIETAL-RELATED CONSEQUENCES OF KATRINA-RELATED DAMAGE This section—Volume VII—of the IPET report assesses the consequences of Hurricane Katrina in a broad range of categories, including: direct economic consequences; indirect economic consequences; human health and safety; social, cultural, and historical; and, environmental. Volume VII contains extensive discussion and data on these five topic areas (the volume and its technical appendices are nearly 900 pages long). Volume VII employs both traditional Corps of Engineers methods and approaches (e.g., use of depth-damage and stage-damage relationships to estimate flood damages) and draws upon methods and reports from other sources (e.g., the FEMA “HAZUS” damage assessment model; McCarthy et al., 2006). The methods employed and results obtained generally are well explained throughout the volume. Volume VII also contains good discussion of uncertainties and how they affected estimates of, for example, flooding depths, depth-damage relationships, and property damage estimates. The accounting of these uncertainties enhances the presentation of results obtained in Volume VII. Volume VII also usefully points out priority areas for future research. The Executive Summary of Volume VII exhibits a trait seen in other sections of the entire report, in that it emphasizes methods and approaches employed, but does not present a clear, succinct summary of primary findings and conclusions. The Executive Summary, however, is followed by a more detailed Summary section that includes a succinct list of the primary economic, environmental, and other consequences of Hurricane Katrina, along with useful discussion of the implications of Katrina’s extensive impacts. RISKS TO NEW ORLEANS AND THE REGION POSED BY FUTURE TROPICAL STORMS The IPET volume on risks to the region posed by future tropical storms is Volume VIII of the report and is entitled “Engineering and Operational Risk and Reliability Analysis.” Volume VIII was the principal focus of the final two years of the IPET study. During its review of the IPET draft reports, the NAE/NRC committee adjusted its course to provide a full report (its fourth report, issued in February 2008; see Box 1-1) that reviewed specifically the IPET Volume VIII. The assessment of the risks to New Orleans and the region posed by future tropical storms (IPET study objective 5 and the topic of Volume VIII) represent important methodological advances, and the June 2008 draft represents an improvement over the 2007 draft that this committee reviewed and reported on (see NRC, 2008a). The IPET developed a sophisticated way to project results from single events into a risk-based framework and this has improved the
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The New Orleans Hurricane Protection System: Assessing Pre-Katrina Vulnerability and Improving Mitigation and Preparedness understanding of vulnerabilities to future storms across the region. A key shortcoming of the Volume VIII risk assessment is that it lacks a succinct and clear presentation of its key findings. A previous report from this NAE/NRC committee (NRC, 2008a) noted problems related to a lack of discussion of results—particularly those regarding the report’s inundation maps. The IPET draft final includes some discussion of varying vulnerabilities in different sections of the city and region, and it does include the inundation maps; this crucial information, though, is scattered and still is not well discussed. Volume VIII contains extensive discussions on the details of technical issues including crest elevations, reach descriptions, overflowing rate models, wave exceedance curves, breach elevation and volume models, and event tree branch probabilities. This extensive technical information overwhelms the discussion of key results and, where those discussions of key results can be found, they tend to be very short with little explanation of their implications. For example, the Risk Analysis Results section in Volume I states that “New Orleans is widely vulnerable to some flooding at the 50-year or 2% frequency of occurrence level if significant pumping capacity is not available” (IPET, 2008, I-134; the same language appears in Volume VIII, as well). It goes on to state that with good pumping capacity, that flood elevations can be lowered and that “There is a small benefit in NOE and a significant benefit in OM, portions of JE, JW, and PL” (IPET, 2008, VIII-134). These are examples of the brevity and lack of elaboration in this important section on results, and they stand in contrast to extensive discussions on technical details in Volume VIII and elsewhere in the report. This contrast is especially important when considering the importance of risk communication. Details on the calculations of exceedance frequencies are important to the technical foundation of the IPET project, and all parties want to be assured that fundamental analyses are sound. Citizens, business leaders, and public officials in New Orleans, however, are likely to be more immediately concerned with IPET study results and their implications for future settlement, rebuilding, and construction activities. Additional examples of this limited discussion of results can be found elsewhere. For example, in the section of Volume VIII on the “100-year Flood Event,” it is stated that, “Without pumping, the majority of the New Orleans area remains vulnerable to moderate to deep flooding (greater than 4 ft.) at the 100-year or 1% frequency of occurrence. The area with the least vulnerability is Jefferson Parish and St. Charles Parish, where flood threats are moderate” (IPET, 2008, VIII-134). These types of statements carry a great deal of important information, but without cross-referencing these findings with maps, or without further elaboration to ensure that non-technical experts clearly understand these terms, the prospects for clear risk communication from the IPET report are diminished considerably. This committee would like to reiterate its opinion that there should be more thorough discussion of these types of results from the IPET report, and that
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The New Orleans Hurricane Protection System: Assessing Pre-Katrina Vulnerability and Improving Mitigation and Preparedness some of this discussion should contain less technical terminology. The public and elected officials will be especially interested in place-specific inundation estimates and what they imply for future activities. The IPET Volume VIII of June, 2008 provides a detailed description of the risk assessment methodology to characterize the potential for failure of HPS levees, flood walls, and related facilities. Although considerable attention is devoted to justification of the climatological and hydrodynamic methods and models, there is little treatment of the approximations and extrapolation of sparse geotechnical data that is also part of applying the risk assessment methodology. A candid discussion of the most important limitations of the risk and reliability models would improve implementation of the modeling results and provide guidance on where and when the results should be applied with caution. This discussion also could identify opportunities for improvement and help formulate a future research agenda for better simulation of the HPS performance. Among the important findings from Volume VIII is a set of inundation maps for the New Orleans metro region. The results conveyed in these maps are of great importance and interest to citizens, businesses, and government agencies that are making plans for resettlement and redevelopment in this region. Volume VIII presents these important inundation maps, but there is only limited discussion of their implications. Volume VIII would be strengthened by adding an explicit, detailed discussion of the inundation maps and their implications for the spatial distribution of risk across the city and the region. Volume VIII also would be strengthened by adding an objective, candid discussion of the main limitations of the risk and reliability models used therein, and areas for future improvement. More thorough discussion of all of Volume VIII’s main findings about future vulnerability to the New Orleans region—especially in layman’s terms that are understandable to most decision makers, citizens, and business owners who wish to read the document—is necessary to help them better understand future vulnerabilities and to assist them in their relocation and reconstruction decisions. ADDITIONAL COMMENTS Discussions of “Lessons Learned” The IPET report includes several “Lessons Learned” sections, which generally are well written and make useful statements regarding nonstructural dimensions of hurricane preparedness, such as evacuation. The importance of evacuation planning and preparedness is emphasized in Volume I and elsewhere in report. For instance, the report notes that “At this time evacuation is the only
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The New Orleans Hurricane Protection System: Assessing Pre-Katrina Vulnerability and Improving Mitigation and Preparedness effective means to substantially reduce loss of life for large hurricane events” (p. I-4), and, “The emergency response preparedness and efficiency of evacuation prior to a storm is a key component to reducing risk to life and human safety” (p. I-5). It also explains clearly that much of the region remains subject to hurricanes and it does a good job at explaining the concept of residual risk—“No matter how well designed an HPS may be, some level of residual risk always remains: risk is never reduced to zero” (IPET, 2008, VIII-12). The Role of Wetlands in Storm Surge and Hurricane Protection The potential virtue of marshes, wetlands and other vegetation in protecting inshore areas from storm surge has been a topic of considerable speculation following hurricane Katrina, particularly given the documented loss of significant areas of marshes in southern Louisiana during the past 50 years. The IPET made a reasonable effort to include the effects of these landscape features in their storm surge and wave modeling with equivocal results. Considerable uncertainty remains about how to properly represent these effects in surge and wave models and in the resulting model sensitivities. Given the major investments that are being discussed for marsh restoration projects in southern Louisiana (see USACE, 2007; State of Louisiana, 2007), and the partial justification for these projects based on their value for increased hurricane protection, it is important that additional efforts be taken to improve understanding of the effects these features have on hurricane wave and storm surge across this region. Interagency Coordination on Flood Inundation Maps In addition to the inundation maps generated in the IPET studies, the Federal Emergency Management Agency (FEMA) is in the process of updating its Flood Insurance Rate Maps (FIRMs) to provide delineation of the 100-year flood elevation for southern Louisiana. Also, the National Hurricane Center (part of the National Oceanic and Atmospheric Administration, or NOAA) has produced a set of maximum flood elevation maps for hurricanes of various categories, tracks, forward speeds, and other variables that are used primarily for evacuation planning. Although IPET, FEMA, and NOAA have different objectives and product needs, these agencies should engage in ongoing communication and coordinate to ensure consistency among their methods and the resulting products.
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The New Orleans Hurricane Protection System: Assessing Pre-Katrina Vulnerability and Improving Mitigation and Preparedness Organization and Discussion of Main Findings The IPET draft final report of June 2008 contains roughly 7,500 pages. A document of this size presents considerable editorial challenges in fully and clearly presenting its main findings and recommendations. The IPET report Volume I, Executive Summary and Overview, contains much interesting and useful information, and readers will turn to it expecting to see primary findings and recommendations. The Volume I Executive Summary is well written, interesting, and informative. Its readability is enhanced by the editorial-type format in which it is presented. There are, however, many disconnections between Volume I’s Executive Summary (ES), and the organization and contents of the rest of the report. For example, the ES concludes that (among other things), “The standard project hurricane (SPH) methodology … is outdated and should no longer be used” (IPET, 2008). It also concludes that “The 100-year de facto standard is far too risky for the continued vitality of our economy…” (Ibid.). These are important findings with which many experts would agree. Nonetheless, it is not clear how or from where these conclusions flow from the IPET analysis presented in the various report volumes. The size of the IPET document makes it difficult to determine quickly where supporting discussions for these and other conclusions appear in the main body of the report. In addition, cross-referencing between Volume I and the rest of the report is confusing and inadequate. As a result, key findings and conclusions based upon the IPET analysis are not as clear as they could be. In a previous report (NRC, 2008a), this committee recommended that, in addition to the full IPET report, that a second document should be prepared “for elected officials and the public” and that this document “could be much shorter and focus on results and implications for reconstruction and resettlement” (Ibid.). The importance of this recommendation has not diminished, and the committee wishes to reiterate this point in the following recommendation. The IPET and the Department of the Army should enlist the services of a firm that specializes in technical writing of scientific and engineering reports to produce a final, summary document of the entire IPET report. The summary should be written in layman’s terminology in order to communicate clearly the IPET study results to decision makers and citizens.