Fourth Report of the National Academy of Engineering/National Research Council Committee on New Orleans Regional Hurricane Protection Projects Review of the IPET Volume VIII (2008) / Chapter Skim
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Fourth Report of theNational Academy of Engineering/National Research Council Committee on New Orleans Regional Hurricane Protection Projects: Review of the IPET Volume VIII
Fourth Report of theNational Academy of Engineering/National Research Council Committee on New Orleans Regional Hurricane Protection Projects: Review of the IPET Volume VIII
Pages 1-16
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design and status of the hurricane protection system pre-Katina; 2. storm surges and waves generated by Hurricane Katrina; 3.
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Successful and prompt completion of Volume VIII and the IPET report is important for several reasons: it is important for the credibility of the U.S. Army Corps of Engineers; it is important to life decisions and financial investments regarding rebuilding and relocation in the New Orleans metropolitan area, and; it is important to ongoing and future analyses of hurricane protection and coastal restoration in southern Louisiana.
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This approach employs a probabilistic framework that includes assumptions and computations regarding: hurricane intensity and frequency; storm surges and waves; performance of levees, floodwalls, closure gates, and pumping stations; and relationships between inundation depths and loss within the parishes of the greater New Orleans region. The approach and methods employed by the IPET in this risk analysis appear to be appropriate for evaluating risks associated with the New Orleans hurricane protection system prior to and following Katrina, and in certain areas they advance the state-of-the-art.
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Volume VIII provides documentation but it is incomplete in some areas and difficult to follow in others. Example: Joint Probability Model The IPET bases its analysis of future hurricane threats on a modified version of the Joint Probability Model (JPM)
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Presentation of intermediate results will enhance understanding of the overall risk results, and independent testing and validation of the individual models and methods employed in the risk analysis. The interim draft Volume VIII, however, contains inadequate information about intermediate results and how these results impact the overall results.
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The most credible estimates of future storm surge and flooding will contain uncertainties, and it is important to explain why such uncertainties exist and what they might imply for future development or construction activities. The interim draft Volume VIII provides few quantitative estimates or qualitative explanation of uncertainties and their implications.
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The use of these test results, and the variability they entail, may introduce another source of uncertainty to the risk analysis. Inadequate Presentation of Inundation Maps Arguably the most important results to be produced within Volume VIII are inundation maps associated with varying hurricane storm surges.
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Greater emphasis on the communication of the key features of these inundation maps would enhance future versions of Volume VIII. Incomplete or Unclear Explanation, Inconsistencies, and Errors Volume VIII contains instances in which the explanation and presentation of important and complex technical details are confusing or inadequate, and perhaps incorrect.
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. These figures contain information regarding overtopping of different sections of the hurricane protection system for pre-Katrina conditions and for current conditions.
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The sum of the errors and inconsistencies gives an impression of a document that was written quickly, with inadequate review and technical editorship. RECOMMENDATIONS FOR STRENGTHENING VOLUME VIII Careful analysis, thorough editing, and consideration of how information is to be presented are needed to improve the interim draft Volume VIII.
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The IPET intends to conduct an assessment of the uncertainties that stem from factors that affect flooding and inundation depths, including occurrence rates of hurricanes, surge and wave elevations, rainfall rates and amounts, and performance of the hurricane protection system. This is to be encouraged, as credible results from the uncertainty assessment will increase confidence levels in modeling results and applications.
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The IPET team should discuss how the fragility curves could be improved through use of more reliable shear strength measurements either in laboratory or field tests. Any steps that have been taken to validate I-wall fragility curves relative to fullscale I-wall tests performed by the Corps of Engineers at the Atchafalaya levees, or from back-calculated safety factors for the 17th Street and London Avenue Canal failure sites, should be described.
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This presentation should include discussion and explanation of the implications of these estimates for rebuilding and reconstruction decisions across the New Orleans metropolitan region. Other Technical Additions and Changes Hurricanes used to conduct a risk analysis for the New Orleans region should be compared to those for which historical records are posted to the website of the National Hurricane Center (NHC)
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Schedule for Completion The IPET was established in October 2005 by the Chief of the Corps of Engineers. The IPET promptly addressed its task of evaluating the performance of the New Orleans hurricane protection system during Hurricane Katrina, with an initial goal of completing its final report by June 1, 2006.
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Adequate resources should be provided to meet this schedule. CLOSING COMMENTS The risk and reliability analysis within the IPET interim draft Volume VIII are a crucial and challenging part of the IPET study.
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The intense effort that resulted in volumes 1-7 of the IPET report has subsided such that the Volume VIII risk and reliability study has taken more than twice the length of time for the rest of the study, and remains incomplete. We encourage the Corps of Engineers to infuse this effort with the resources necessary to promptly complete the Volume VIII study, keeping in mind this NAE/NRC report's recommendations for improvement.
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