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THE NATIONAL ACADEMIES

Advisers to the Nation on Science, Engineering, and Medicine

National Academy of Engineering

National Research Council

500 Fifth Street, NW
Washington, DC 20001
www.nationalacademies.org

February 21, 2006

The Honorable John Paul Woodley

Assistant Secretary of the Army, Civil Works

108 Army Pentagon
Room 3-E446
Washington, D.C. 20310-0108

Dear Assistant Secretary Woodley:

This letter constitutes the first report from the Committee on New Orleans Regional Hurricane Protection Projects, which was recently formed through the National Academy of Engineering (NAE) and the National Research Council (NRC) at your request. It is my pleasure to chair this committee that is charged to review the data, analyses, and conclusions reached by the Interagency Performance Evaluation Task Force (IPET). A roster of our committee membership and its statement of task are attached.

BACKGROUND

On August 29, 2005, Hurricane Katrina struck the U.S. Gulf Coast. The storm made landfall at two sites, first near Buras, Louisiana at 6:10 a.m. local time, then later near Pearl River, Mississippi at 9:45 a.m. local time. The storm produced a massive surge of water on the continental shelf and coastal regions that overtopped and eroded away levees and flood walls along the lower Mississippi River in Plaquemines Parish, along the eastern side of St. Bernard Parish, along the eastern side of New Orleans East, and in locations along the Gulf Intracoastal Waterway and the Inner Harbor Navigation Canal. Surge water elevated the level of Lake Pontchartrain and shifting storm winds forced the lake water against the levees and floodwalls along its southern shores and the adjoining drainage canals. Although most of the protection structures along Lake Pontchartrain were not overtopped, hydraulic forces caused breaches of floodwalls along New Orleans’ 17th Street Canal and the London Avenue Canal. Flooding in the New Orleans region resulted in the loss of hundreds of lives and catastrophic property and infrastructure damage, ranking it among the largest natural disasters in U.S. history.



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Structural Performance of the New Orleans Hurricane Protection System During Hurricane Katrina: Letter Report THE NATIONAL ACADEMIES Advisers to the Nation on Science, Engineering, and Medicine National Academy of Engineering National Research Council 500 Fifth Street, NW Washington, DC 20001 www.nationalacademies.org February 21, 2006 The Honorable John Paul Woodley Assistant Secretary of the Army, Civil Works 108 Army Pentagon Room 3-E446 Washington, D.C. 20310-0108 Dear Assistant Secretary Woodley: This letter constitutes the first report from the Committee on New Orleans Regional Hurricane Protection Projects, which was recently formed through the National Academy of Engineering (NAE) and the National Research Council (NRC) at your request. It is my pleasure to chair this committee that is charged to review the data, analyses, and conclusions reached by the Interagency Performance Evaluation Task Force (IPET). A roster of our committee membership and its statement of task are attached. BACKGROUND On August 29, 2005, Hurricane Katrina struck the U.S. Gulf Coast. The storm made landfall at two sites, first near Buras, Louisiana at 6:10 a.m. local time, then later near Pearl River, Mississippi at 9:45 a.m. local time. The storm produced a massive surge of water on the continental shelf and coastal regions that overtopped and eroded away levees and flood walls along the lower Mississippi River in Plaquemines Parish, along the eastern side of St. Bernard Parish, along the eastern side of New Orleans East, and in locations along the Gulf Intracoastal Waterway and the Inner Harbor Navigation Canal. Surge water elevated the level of Lake Pontchartrain and shifting storm winds forced the lake water against the levees and floodwalls along its southern shores and the adjoining drainage canals. Although most of the protection structures along Lake Pontchartrain were not overtopped, hydraulic forces caused breaches of floodwalls along New Orleans’ 17th Street Canal and the London Avenue Canal. Flooding in the New Orleans region resulted in the loss of hundreds of lives and catastrophic property and infrastructure damage, ranking it among the largest natural disasters in U.S. history.

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Structural Performance of the New Orleans Hurricane Protection System During Hurricane Katrina: Letter Report The Interagency Performance Evaluation Task Force—comprised of experts from more than 40 public, private, and academic organizations—was formed in October, 2005, by U.S. Army Corps of Engineers Commander and Chief of Engineers, Lieutenant General Carl Strock. The IPET mission is to provide credible and objective scientific and engineering answers regarding the performance of the New Orleans metropolitan hurricane protection system during and after Hurricane Katrina. The IPET is collecting and analyzing an extensive amount of data in its mission to evaluate engineering and related aspects of the system, including design specifications, the condition of the system before Hurricane Katrina, system performance during and after Hurricane Katrina, the nature of the storm and wave forces to which the system was subjected, and the consequences and risks of hurricanes across the region. To assist the IPET, an American Society of Civil Engineers (ASCE) external review panel (ERP) is providing oversight and ongoing dialogue. IPET documents reflect the advice being offered by the ASCE ERP. This NAE/NRC committee will issue three reports in 2006. This letter is the first of those three reports and it represents the committee’s consensus observations of the IPET effort to date. Its purpose is to review and provide recommendations on the adequacy of the nature of the data being collected by the IPET and ASCE ERP teams, consistency of those analyses with accepted engineering approaches, and additional data that will be important to the IPET study (see attached statement of task). The letter is based upon a review of the IPET first report, issued on January 10, 2006 (www://ipet.wes.army.mil; last accessed on February 2, 2006), supplemented by information presented by IPET team members and by representatives of the ASCE ERP at our committee’s first meeting, held in New Orleans on January 18, 20061. CONTEXT OF THE INTERAGENCY PERFORMANCE EVALUATION TASK FORCE STUDIES The New Orleans and southeastern Louisiana hurricane protection system includes many engineering, geologic, hydraulic and hydrologic, administrative, and economic and cultural features that interact in complex ways. The levees, floodwalls, and other protective structures in New Orleans and southeast Louisiana have been constructed in a region of active alluvial deposition, subsidence, and fluvial dynamics. The Mississippi River delta, for example, has changed location several times in the past 5,000 years. The region is underlain by deep deposits of recent sediments with high clay content and by sites with varying rates of geologic subsidence—conditions that pose many stringent engineering challenges. In addition to geologic and engineering considerations, there is a long history of piecemeal construction and maintenance of the system. Construction of levees and floodwalls in the New Orleans area dates to early stages of urban development in the area. An important event in this history was Hurricane Betsy in 1965. Betsy was responsible for 75 deaths and billions of dollars of property damage, prompting efforts to create a regional program of hurricane 1   IPET investigations represent an ongoing and rapidly evolving effort. This letter does not comment on data or analyses that the IPET may have produced after January 18, 2006.

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Structural Performance of the New Orleans Hurricane Protection System During Hurricane Katrina: Letter Report protection. In the aftermath of Betsy, Congress authorized construction of a hurricane protection system to protect areas in the vicinity of Lake Pontchartrain and surrounding parishes from storm surges. The various projects that make up this system are paid for with a combination of federal, state, and local funds. The decision-making and investment processes that have led to the development of the system have involved numerous stakeholders for more than 50 years. Primary responsibility for design and construction of hurricane protection projects has been assigned to the U.S. Army Corps of Engineers. Actual project construction has been contracted to numerous private sector firms. Once projects are constructed and fully completed, responsibility for their maintenance is often assigned to local authorities. Since 1965, approximately 125 miles of levees, concrete floodwalls, and other structures have been built in the New Orleans region. Not all projects authorized for construction by the U.S. Congress, however, had been completed as of August, 2005. The hurricane protection structures that existed in New Orleans and the surrounding area in August 2005 were not a single system constructed as part of a unified plan; rather, the system had been added to and repaired by different administrative units—federal, state, and local—operating with different mandates, levels of resources, and staff backgrounds and capacities. No single entity has been fully “in charge” of constructing and maintaining all hurricane protection structures, complicating efforts at systematic repair and construction and efforts to retrieve and assess data on historical decisions and pre-existing conditions. OBSERVATIONS AND COMMENTS ON THE IPET FIRST REPORT It is against this background that the IPET is conducting its studies. The data collection and analytical components of these studies would be demanding under any circumstances. They are, however, being conducted on a compressed schedule—approximately nine months—adding to this analytical challenge. The work required to identify, recruit, and coordinate the efforts of federal and non-federal engineers and scientists, lay out an overall study structure and work plan, convene numerous meetings and conference calls, and begin data analysis and model construction on many fronts, has been considerable. Our committee is impressed with the extent of the IPET efforts and commends the IPET for the energy devoted to its tasks and for the progress achieved in a short amount of time. This letter divides the key areas in which IPET activities could be strengthened into three broad areas: a) system-wide and interdisciplinary issues, b) geotechnical data and investigations, and c) hydrology, hydraulics, and hurricane surge and wave analysis. We offer several recommendations for improving the data gathering and analytical efforts within the IPET initiative. With a project like IPET, and its limited timeline for accomplishing several challenging studies, it might be tempting to identify metrics for prioritization in order to accomplish first the most important tasks, leaving lower priority tasks to be accomplished later. Our letter report offers no relative priorities regarding its recommendations. All recommendations offered are important to achieve a comprehensive, sound set of studies within the IPET. Moreover, some of the metrics that might be used to set relative priorities include

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Structural Performance of the New Orleans Hurricane Protection System During Hurricane Katrina: Letter Report factors that may relate to budget and policy decisions, some of which go beyond the committee’s charge and resources. System-wide and Interdisciplinary Issues Report Structure and Coherence For the most part, the IPET first report presents a set of objectives that provide a clear set of metrics for evaluating overall performance of the hurricane protection system during and after Katrina (see p. 6-7 of the IPET first report). As noted later in this report, some metrics are in need of further clarification. These objectives of the IPET focus on answering a series of questions related to a) the flood protection system, b) the storm, c) performance (of the protection system), d) consequences of Katrina-related damage, and e) risks to New Orleans and vicinity from future hurricanes and tropical storms. These IPET report objectives appropriately state the importance of understanding overall, system-wide performance of hurricane protection for the New Orleans region. This system-wide thinking and presentation is, however, not well established in the IPET first report. Data collection activities and initial analytical efforts, while impressive in some regards, are not clearly presented in the IPET first report in the context of the stated objectives, thereby clouding the rationale behind some of the efforts to date. A chart presented in Figure 2, p. 11, of the IPET first report identifies the 10 study topics and plans for incorporating results from each study area into the overall study2. The IPET is encouraged to elaborate on this overall IPET program structure and to enhance explanations of the transitions and linkages between its 10 study areas in its subsequent reports. It is particularly important to demonstrate clearly how ongoing efforts within the 10 study areas will contribute to fulfillment of the five primary objectives of the IPET mission. This should help the IPET prioritize efforts during the remainder of the project and enhance progress toward a more systematic and interdisciplinary investigation. It will also help explain the essence of the IPET effort to the non-expert and help ensure that the study employs a common sense approach toward meeting its objectives. Systems-wide Perspectives Data collection and analytical efforts to date appear to be focused on particular aspects of the event and specific sites, as opposed to system-wide analyses. For example, the IPET first report has a strong focus on analyzing conditions at specific breach sites, with less emphasis on 2   These 10 study areas are: data collection and management; geodetic vertical and water level datum assessment; hurricane surge and wave analysis; hydrodynamic forces analysis; geotechnical structure performance analysis; floodwall and levee system performance analysis; pumping station performance analysis; interior drainage/flooding analysis; consequence analysis; and risk and reliability analysis.

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Structural Performance of the New Orleans Hurricane Protection System During Hurricane Katrina: Letter Report evaluating potential deterioration in other areas of the system and their vulnerabilities in future storm events. It is not clear if the IPET plans to conduct site investigations elsewhere in the levee system where there may be potential foundation problems. But issues of overall system strength and vulnerabilities will be of crucial importance in identifying ways to enhance future system performance and levels of protection. There is some evidence that the IPET plans to place more emphasis on systems perspectives as its efforts evolve. For example, at the January 18, 2006 meeting, the IPET team provided a slide that depicts “Assessment of Entire System,” which suggests there are plans to designate different floodwall and levee sections according to seven different categories. The IPET is encouraged to move forward with these types of classifications and evaluations of the regional hurricane protection system. Analysis of system-wide condition will also be crucial in enhancing public confidence in the hurricane protection system. Mapping and Visualization A greater use of modern geographic information system (GIS) mapping techniques for purposes of both analysis and presentation would help the IPET conduct its desired system-wide approach. The introductory and opening sections of the IPET first report contain only a single map (several other maps are presented later in the 10 IPET team reports and appendixes), and there is scant evidence that data collection efforts are being conducted with any consideration as to how they fit into a wider spatial context. A greater use of contemporary GIS mapping technologies and techniques would enable the IPET to produce a system of overlay maps of different aspects of the system, such as geology, previous topography and land use, floodwalls, levees, soils, administrative units, and time series of maps of protection systems as they have been constructed across the region. Such a system of overlay maps would be useful for analysis, visualization, and communication among IPET teams and with stakeholders including government officials, interested citizens, and the media. Greater use of geographic information systems would also enhance the ability to analyze and present individual sites within the larger context of the entire system. The IPET team should aggressively seek opportunities to extend the use of GIS within its investigations. Data Collection and Accuracy One IPET objective is to answer the question: “Following the immediate repairs, what will be the quantifiable risk to New Orleans and vicinity from future hurricanes and tropical storms?” As noted, the IPET program includes extensive data collection efforts and a great deal of highly technical analysis. Some IPET study stakeholders may have unclear expectations about the quality and completeness of the information that will ultimately result from the IPET effort. The IPET should characterize the level of confidence it has in the data being used, as estimates of uncertainty and explanations regarding relative accuracy and reliability of its data could make IPET investigations more relevant and useful to the public and others making risk-based decisions about future actions.

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Structural Performance of the New Orleans Hurricane Protection System During Hurricane Katrina: Letter Report Other, more specific points include a lack of clarity regarding how uncertainties related to wind field data and surge height measurements will be addressed, and a concern that the investigations of the impacts of loose barges on floodwalls and other structures has not received appropriate emphasis to date. Designs of levees and other protective structures should consider the various types of maritime commercial vessels that travel the region’s canals. From the standpoint of obtaining a more complete set of data, two additional areas are recommended for review and integration. First, tree growth and the encroachment of adjacent structures appear to have had some effects on the integrity and performance of levees; these effects deserve additional attention. Second, local commercial enterprises, such as petroleum companies and their subsidiaries and related service providers, may have captured important environmental information throughout the storm event. Efforts should be made to obtain data on wind velocities and surge and wave heights that may be available from these sources. Geodetics It is clearly important to establish state-of-the art and accurate geodetic control, and that references to past datums be clarified to the extent possible. The IPET has expended a great deal of effort in this realm. There is, however, little evidence (e.g., maps) that a comprehensive data set is actually being assembled. Future IPET efforts in this important endeavor should be aimed at overall comprehensiveness and clarity of purpose. IPET Schedule and Region-wide Recovery Finally, the IPET has been tasked to carry out several challenging data collection and analytical efforts on a very short timeline, which is affecting the organization and progress of the entire program. The final IPET products are scheduled to be completed by June, 2006, which represents a nine-month time period for the entire study. The time constraints imposed on the IPET are not conducive to thoughtful and comprehensive analysis and may force IPET team members, many of whom appear to be working around the clock, to make hasty decisions with little time to learn and to make appropriate mid-course corrections. The schedule provides little time to consider carefully how, and by whom, IPET results will eventually be applied. Nor does this schedule lend itself to the efficient conduct of review processes that could contribute to meaningful IPET mid-course program adjustments and improvements. Given these constraints, expectations for fully integrated studies of uniform high quality to be produced by June 1, 2006 appear to be optimistic. We note that the IPET activities may produce information to support current decisions being made by Task Force Guardian regarding levee repairs prior to the upcoming hurricane season but that is not their principal objective. Thus, the rationale for such an accelerated timeline for the advanced and complex assessments being carried out by the IPET is not clear.

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Structural Performance of the New Orleans Hurricane Protection System During Hurricane Katrina: Letter Report The IPET effort could also be enhanced by some explanation regarding how IPET activities fit into the larger context of restoration and reconstruction plans for New Orleans and southeastern Louisiana. The pace and variety of recovery activities in the region are considerable, and the IPET studies are but one part of this overall picture. Issues such as administrative roles and responsibilities for maintaining the hurricane protection system, and overall plans for the New Orleans recovery effort, are beyond the scope of activities with which the IPET has been charged. But, unless there is some strategy for applying IPET study results, the good efforts of the IPET team may not be put to their best use—or even applied at all. IPET activities should be framed clearly and presented in the larger context of New Orleans regional recovery efforts. Geotechnical Data and Investigations System-Wide Characterization A comprehensive, system-wide site investigation program is needed to establish a baseline of foundation conditions and to evaluate the performance of the region’s hurricane and flood protection systems. This data collection is necessary to address the IPET objective of determining whether similar conditions, which can lead to failure, exist elsewhere in the system. Characterizing soil conditions along hundreds of miles of levees, to a degree suitable for meeting IPET objectives, is a challenging task. The IPET should clarify the scope and schedule for this investigation, how the data will be fused with archival information, and what procedures will be used to represent and evaluate the ground conditions. Greater emphasis and better explanation of region-wide geologic conditions could help promote IPET systems-wide approaches and analyses. This would help both analysts and the general public understand better, for example, the extent to which post-Katrina failures represented unique hydraulic loading, structural wall design, and foundation conditions, or whether similar conditions exist elsewhere in the levee system. This type of knowledge will be crucial in improving overall system preparedness and performance. Discussions with IPET team members suggest that IPET is working to develop and present this picture of overall regional geology, and the IPET is encouraged to continue developing this portrayal of regional geologic conditions. Data Gathering The Data Repository, described in Appendix G in the first IPET report, is organized to be comprehensive, with detailed information for each part of the New Orleans levee and flood wall system, including base maps, climate, design criteria, field investigations, geology, hydrology, lab test data, modeling, soil conditions, and other data. This is an appropriate approach to systematic collection and archiving of information, and the IPET is encouraged to develop and apply data in a timely manner for engineering analysis.

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Structural Performance of the New Orleans Hurricane Protection System During Hurricane Katrina: Letter Report There is currently little indication of how data are being collected and applied on a site-specific and system-wide basis to address fundamental questions about the physical characteristics of the levees and underlying ground conditions. Moreover, there is little information about in situ soil properties in the report at any location in the levee system. To provide a credible assessment of the levees and their failure mechanisms, the IPET team should, at a minimum: describe relevant features of regional and local geology; display the expected geological profile (with physical and index properties of the underlying soils) together with the levee/wall designs, and provide best estimates of current and as-built conditions along all reaches of the federal hurricane protection system. begin creating a comprehensive GIS data base in which these data can be stored, evaluated, and spatially displayed. A program of well designed in situ tests would be important in expanding the reach of the study and to promote a more comprehensive evaluation of the stability of the system. To the extent that the IPET team may have made post-January 18 progress on this front, they should be encouraged to continue to do so. 17th Street and London Avenue Breaches Foundation conditions are of particular importance at the sites of the breaches at 17th Street and London Avenue Canals (where there is no evidence of overtopping). Preliminary soil profiles were presented for both sites at this committee’s January 18, 2006 meeting, but no subsurface profiles were contained in the IPET first report. As these local forensic studies are being conducted, the following information would be especially useful in improving understanding of the mechanisms behind these breaches: Detailed plans showing the availability of archival boring information, a location plan with sites of new borings, supplementary field tests (e.g., vane shear tests) and other in situ tests that have been used to refine stratigraphic profiling and estimation of in situ soil properties, notably piezocone penetrometer profiles3. A comprehensive study of soil properties through a combination of field and laboratory testing. Based on the information presented at the January 18, 2006 meeting, the stability of the 17th Street site and the undrained shear strengths of the clays (levee fills, lacustrine clays) and organic soils (swamp, marsh deposits) are of critical importance for levee wall stability. The IPET team presented some recent data from relatively crude laboratory shear tests (also known as “UU triaxial tests”). These are inadequate, however, to fully 3   Piezocone tests are cone penetration tests (CPT) that measure pore water pressure at one or several locations on the penetrometer surface. Cone penetration testing with pore water pressure measurements provide a more reliable determination of stratification and soil type than standard CPT.

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Structural Performance of the New Orleans Hurricane Protection System During Hurricane Katrina: Letter Report understand the failure mechanisms. A more reliable practice in soft clay conditions would entail a combination of in situ piezocone tests (to establish spatial variability) and consolidated-undrained shear tests on high quality samples following procedures such as SHANSEP (Ladd and Foott, 1974) that have been extensively validated in the local area. Field vane shear tests will also provide useful direct measurements from which to estimate in situ undrained strength. Piezocone tests will also be helpful in evaluating in situ shear strength of beach deposits that are likely to be important at the London Avenue breach. The IPET first report provided little information on the likely failure mechanisms at either the 17th Street or London Avenue breaches. And although the limit equilibrium and finite element analyses listed in the IPET report are reasonable, accepted engineering practice would entail a summary of current and estimated soil properties and an initial evaluation of potential failure mechanisms at these key breaches. This information is important to explain and justify the re-design of the flood walls (i.e., the introduction of pile supported T-wall sections and very long sheet-pile cut-offs). The IPET first report emphasizes centrifuge modeling of the failed sections, with their original I-wall designs. This emphasis is not appropriate given the current lack of site characterization information and performance analyses. This type of physical scale-modeling can be useful in confirming/validating local failure mechanisms; however, it also introduces modeling challenges such as proper simulation of consolidation conditions of model peat and clay layers, and difficulties in consistent scaling of deformation, strength, and flow properties (for mechanisms involving piping and internal erosion). It is unlikely that centrifuge tests will be able to simulate fully the field conditions, and the expectations for such tests should be qualified and managed appropriately. It would likely be more effective to use centrifuge testing to evaluate performance of redesigned T-wall sections. Another limitation of the IPET first report is the lack of a site investigation plan. Such a plan is necessary to establish a baseline on foundation conditions that can be used to evaluate hurricane protection and levee system performance. Although the IPET plans to collect archival soil boring data throughout the system, the only new site investigation data are those obtained as part of the local forensic investigations, such as those at 17th Street and London Avenue canal breaches. Hydrology, Hydraulics, and Hurricane Surge and Wave Analysis Hydrology and Hydraulics Fundamental to the construction and evaluation of a hurricane protection system are studies of the hurricane storm surge and attendant wave environment for which the system has been designed. With regard to evaluations of the impacts of Katrina, several questions arise: Did the existing system fail because it was constructed or maintained improperly? Or did it fail

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Structural Performance of the New Orleans Hurricane Protection System During Hurricane Katrina: Letter Report because the design criteria were exceeded? Or was it a combination of both? There is a policy question of identifying the acceptable level of risk associated with hurricane preparedness plans, and the designs that will provide appropriate levels of protection. Furthermore, knowledge of hurricanes and expertise in modeling their effects, as evinced in the IPET analyses, have advanced since standard project hurricane criteria were defined decades ago for the various elements of the New Orleans hurricane protection system. Future risk assessments should be based on this new knowledge. Another question raised within our committee’s discussions is: “What is the authorized level of protection?” The IPET data analysis task includes specification of the design criteria for the authorized level of protection. Is this level based on the “standard project hurricane?” Or is it the original crown elevations of levees and floodwall? Or is it a one-in-two hundred-year hurricane? The IPET should clarify answers to these questions, as these answers will affect how the IPET addresses parts of its mission statement. The IPET report uses the terms “frequency of exceedance of water levels” and “probability of flooding.” The IPET should clarify the meaning of these important terms and ensure their consistent use throughout its study and reports. Hurricane Surge and Wave Analysis Accurate simulation of storm surge and wave conditions depend upon the accuracy of the forcing data (e.g., wind and pressure fields), the bathymetric and topographic data, and the physical processes represented in the storm surge and wave models. Uncertainties in data, model formulation, or in model parameterization of physical processes will all contribute to errors in model results. Although several storm surge and wave models have been developed for different applications, there is no perfect model that includes all processes for all situations. Fulfillment of IPET objectives to assess storm-related conditions during Hurricane Katrina and the future risks associated with the current protection system require that the storm surge and wave models capture the dominant features and processes of the study area The IPET has placed a strong emphasis on hurricane surge and wave analysis and has made good progress in this area. Future efforts should include clearly documenting how the dominant physical processes are represented and parameterized in the corresponding models. The IPET should, for example, clarify how its surge model represents bottom friction over different bottom types and topographic features, and how the storm surge model is being coupled with the wave model. Efforts should also be devoted to systematically evaluating how uncertainties in forcing data, bathymetric and topographic data, model formulation, and model parameterization affect model simulations, and thereby verify expected uncertainties in model results. When possible it may be helpful to disaggregate parts of the models to identify sources of uncertainty or error at the component level (e.g., in the wind field vs. the surge model). A

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Structural Performance of the New Orleans Hurricane Protection System During Hurricane Katrina: Letter Report thorough understanding of the sensitivity and errors in the wave and surge models will be particularly helpful for meeting IPET objectives mentioned above. Within these modeling exercises, it is also important to assess the roles of features such as man-made structures and topography and bathymetry on surge and wave evolution and heights, and spatial and temporal inundation patterns. These exercises should utilize ensembles of model runs based on a suite of hurricane parameters (e.g, size, intensity, track, central pressure). These ensembles should reflect a variety of possible storms, including past storms that have affected various areas across the Gulf of Mexico, as well as possible future events that might be influenced by climate change and warmer sea surface temperatures. The combination of these scenarios, linked with different probabilities, would provide a more quantitative and complete bases for hurricane protection system design than a more traditional approach that is based on a standard project hurricane. CLOSING COMMENTS When a large, comprehensive field study of the scope of the IPET investigation is undertaken, it is vital to carefully specify during the initial planning stages what data are to be collected, how they are to be collected, and how they are to be presented, and to list the analysis to be conducted. Doing so in a study’s early stages is even more important when several entities are involved in the study. In the case of the IPET studies, all tasks to be pursued should be planned to fit into and support the goal of the parent study, which should ultimately enable the design of a hurricane protection system to adequately protect New Orleans. In a politically charged study such as this one, it is tempting to get into the field immediately in order to show that something is being done. Unfortunately, if a clear, definitive, and system-wide approach is not established at the beginning, the ultimate results may well turn out to be less than desired. Our committee recognizes the challenges that the IPET faces in setting forth such a clear plan. We offer this letter report in the hope of enhancing the overall IPET strategy and to ensuring steady progress as IPET proceeds with its investigations. The IPET has been asked to perform several complicated, time-consuming, and data-intensive tasks on a short time line. The effort is in many ways unprecedented and impressive progress has been made on several fronts in the task force’s four months of existence. In our review of the IPET first report, we concluded that progress across the 10 study areas has been mixed. To summarize this first, letter report from our NAE/NRC committee, this closing section reiterates our group’s findings and recommendations, which fall into three broad areas: system-wide and interdisciplinary issues; geotechnical data and investigations; and hydrology, hydraulics, and hurricane surge and wave analysis. There should be stronger emphasis on explaining connections between data collection efforts and overall study objectives, and in explaining linkages and transitions among the 10 study topics. There should be stronger emphasis on evaluating overall, regional hurricane protection system strength and vulnerabilities.

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Structural Performance of the New Orleans Hurricane Protection System During Hurricane Katrina: Letter Report Geographic information systems for analysis, visualization, and communication should be used to a greater extent. IPET should characterize the level of confidence it has in the data it is gathering, which should include estimates of uncertainty and explanations regarding relative data accuracy and reliability. Future efforts in the useful geodetics program should aim toward comprehensiveness and a clear explanation of program purpose. The expectation for a complete set of fully integrated studies of uniform high quality by June 1, 2006 may be optimistic. The IPET study would be enhanced by some explanation of how IPET activities fit into the larger context of overall recovery. Efforts at gathering data on in situ soil properties and on soil and geologic profiles, and on conducting comprehensive studies of soil properties, should be strongly emphasized. There should be a stronger emphasis on creating estimates of foundation conditions and related physical and engineering properties of the entire hurricane protection system. A map of region-wide geologic and soil conditions should be compiled and utilized. Questions surrounding the concepts of authorized level of protection and standard project hurricane should be clarified. The accuracy of input data and the processes of parameterizing physical processes should be clarified, and an ensemble approach to modeling impacts of future hurricanes should be employed. We offer this letter report in the spirit of constructive criticism and hope that its observations and recommendations are useful in helping refine and improve progress within the IPET program. We greatly appreciate the collegiality and cooperative spirit and actions extended by IPET team members, as well as input and advice offered by you and your staff, the Corps of Engineers New Orleans District Office, members of the ASCE ERP, and members of Task Force Guardian and Task Force Hope. We look forward to future interactions with these groups and individuals and to playing some part in helping improve hurricane preparedness for residents of the City of New Orleans and southeastern Louisiana. In closing, I note that this letter report reflects the consensus of the NAE/NRC committee and has been reviewed in accordance with standard NRC review procedures. We appreciate the opportunity to advise you on the important and challenging initiative. Sincerely, G. Wayne Clough, Chair NAE/NRC Committee on New Orleans Regional Hurricane Protection Projects

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Structural Performance of the New Orleans Hurricane Protection System During Hurricane Katrina: Letter Report Committee Membership G. Wayne Clough, Chair, Georgia Institute of Technology, Atlanta Rafael L. Bras, Massachusetts Institute of Technology, Cambridge John T. Christian, consulting engineer, Waban, Mass. Jos Dijkman, WL/Delft Hydraulics, Delft, The Netherlands Robin L. Dillon-Merrill, Georgetown University, Washington, D.C. Delon Hampton, Delon Hampton and Associates, Washington, D.C. Richard A. Luettich, University of North Carolina, Morehead City Peter Marshall, Burns and Roe Services, Virginia Beach, Virg. David H. Moreau, University of North Carolina, Chapel Hill Thomas D. O’Rourke, Cornell University, Ithaca, N.Y. Risa I. Palm, Louisiana State University, Baton Rouge Kenneth W. Potter, University of Wisconsin, Madison Y. Peter Sheng, University of Florida, Gainesville Robert H. Weisberg, University of South Florida, St. Petersburg Andrew J. Whittle, Massachusetts Institute of Technology, Cambridge

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Structural Performance of the New Orleans Hurricane Protection System During Hurricane Katrina: Letter Report STATEMENT OF TASK Hurricane Katrina and the subsequent flooding of much of the New Orleans metro area prompted many questions about the geotechnical and hydraulic conditions and performance of the city’s hurricane protection system. To help provide credible scientific and engineering answers regarding the performance of this system, an Interagency Performance Evaluation Task Force (IPET) has been convened. The IPET effort is being led by the U.S. Army Corps of Engineers. The IPET is also working with a review team from the American Society of Civil Engineers (ASCE). The IPET, which includes both federal and non-federal scientists and engineers, is divided into ten teams focusing on different topical areas*. The IPET is focusing its investigation on 3 primary topics: a) design capacity of the hurricane protection system, b) forces exerted against the system and system response, and c) factors that resulted in overtopping, breaching, or failure of levees and floodwalls. The IPET report on the structural performance of the hurricane protection system is due on May 1, 2006 (the final IPET report on the entire study is due on June 1, 2006). This NRC/NAE committee will focus its review on the following tasks: review the data gathered by the IPET and the ASCE teams and provide recommendations regarding the adequacy of those data, as well as additional data that will be important to the IPET study and should be gathered; review the analyses performed by the IPET and ASCE to ensure their consistency with accepted engineering approaches and practices; review and comment upon the conclusions reached by the IPET and ASCE teams, and; seek to determine lessons learned from the Katrina experience and identify ways that hurricane protection system performance can be improved in the future at the authorized level of protection. The NRC/NAE committee will issue three reports: a preliminary, letter report that comments on the adequacy of the nature of the data being collected by the IPET and ASCE teams (due in February 2006); an interim report that represents the midpoint of the committee’s evaluation and project (due June 1, 2006), and; a final, comprehensive report (due in September 2006) that summarizes the committee’s evaluation of the IPET/ASCE report on structural performance of the hurricane protection system. The timeline for these three NRC/NAE reports conforms with plans regarding IPET report progress. IPET reporting meetings are scheduled for January 2006 (30%), March 2006 (60%), and May 2006 (90%). The first two NRC/NAE reports will be drafted and issued following the review and evaluation of the IPET 30% and 60% completion reports, respectively. The third NRC/NAE report will be based upon the IPET/ASCE report (due May 1, 2006) on structural performance of the hurricane protection system. *   The committee’s review will focus on the analysis of IPET teams in the areas of: data collection and management (perishable, systems data, and information management), interior drainage systems models, numerical models of the Hurricane Katrina surge and wave environment, storm surge and wave physical modeling of hydrodynamic forces and centrifuge breaching, geodetic vertical survey assessment, and the analysis of floodwall and levee performance.