Third Report of the National Academy of Engineering/National Research Council Committee on New Orleans Regional Hurricane Protection Projects (2006) / Chapter Skim
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Third Report of the NAE/NRC Committee on New Orleans Regional Hurricane Protection Projects
Third Report of the NAE/NRC Committee on New Orleans Regional Hurricane Protection Projects
Pages 1-16
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design and status of the hurricane protection system pre-Katrina; 2. storm surges and waves generated by Hurricane Katrina; 3.
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The report concludes with a short Summary. EXECUTIVE SUMMARY OF THE IPET REPORT The IPET June 1, 2006, Final Draft includes a 50-page Executive Summary and Overview that summarizes key concepts and findings.
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Presentation of Key Concepts and Findings The IPET June 1, 2006, Final Draft Executive Summary is presented in a multilayered structure, with "overarching findings," "principal findings," "detailed findings," and "overarching lessons learned." A summary might be organized in many different ways; but the relations among these varied layers are not clear and these tiers do not help explain the overall IPET report structure and key concepts and findings. Much of the Executive Summary is written at a general level and is not well connected to the analyses that underpin the body of the report.
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"2 Of the five report objectives, this is the most future oriented, as the others focus on evaluations of events before and during Hurricane Katrina. The IPET June 1, 2006, Final Draft defers discussion of these issues until the risk analysis portion of the study is completed.
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It is also important that the public appreciate the value of the IPET's extensive efforts. · The Executive Summary in the IPET June 1, 2006, Final Draft is not fully consistent with the body of the report.
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, and a summary of the regional geology was included in subsequent IPET reports. Although reference to regional geology is made in Appendix II, Volume V, the level of discussion is somewhat limited: regional geology is described in a single paragraph in Volume V in the June 1, 2006, Final Draft and is absent from the Executive Summary.
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GEOTECHNICAL CONCEPTS AND ANALYSES Volume V of the IPET June 1, 2006, Final Draft addresses the performance of the Hurricane Protection System during Hurricane Katrina, focusing on two lines of investigation: (1) studies of breaches that have been attributed to premature3 foundation failures of I-wall sections at the 17th Street, London Avenue, and Inner Harbor Navigation Canal (IHNC)
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Although the phenomenon of gap formation has been investigated in depth (including the use of centrifuge tests) , undrained shear strength of marsh and clay deposits has been investigated in an uneven manner, with important data, especially direct simple shear strength data, absent in the IPET June 1, 2006, Final Draft.
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4. The IPET June 1, 2006, Final Draft is the first of the IPET reports to provide information on the four breaches that occurred along the IHNC.
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The IPET June 1, 2006, Final Draft attributes the large "scatter" in previous laboratory strength measurements to natural soil variability. In fact, the sampling procedures, test specimen selection, and use of unconsolidated (UU and UC)
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It is not clear why the IPET calculations have been restricted to circular arc failure mechanisms, which apparently are not the critical mechanisms associated with levee breaching, as they are inconsistent with Finite Element analyses and physical model tests the IPET has conducted. The IPET team has not reported on analyses for planar and other alternative sliding surfaces and has thus opened itself to criticisms of its conclusions.
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selecting and placing soils to resist erosion, including armoring. RISK AND RELIABILITY Volume VIII of the IPET June 1, 2006, Final Draft entitled "Engineering and Operational Risk and Reliability Analysis" is structured to provide findings central to many of the five IPET report objectives, namely, estimates regarding risks of future storms and of the structural reliability of the hurricane protection system.
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Furthermore, a thorough error analysis should be performed to determine the uncertainty in the final results obtained from the Joint Probability Method. A rigorous error assessment will be critical for establishing the level of confidence that can be placed in results of the risk and reliability analysis.
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Yet, the IPET report does not provide information on this most important aspect of the risk analysis -- what surge levels will the city be protected against? Instead, the IPET risk analysis relies on a joint probability approach that implicitly includes surge heights without explicitly providing this fundamental information.
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This exercise would have the added benefit of providing an assessment of how the surge and waves due to Katrina compare with those previously estimated for the SPH. · To complement its joint probability method results, the IPET should create a set of hurricane scenarios that simulate a variety of possible future storm conditions in the greater New Orleans region.
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The IPET June 1, 2006, Final Draft contains weaknesses in its Executive Summary, geotechnical concepts and analyses, and risk and reliability modeling that will need to be remedied for the document to be both technically credible and a useful guide for citizens and elected officials. Connections between the report's Executive Summary and the body of the report are often difficult to discern.
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