IPET Report 3 Vol VIII

The term “reliability” is intended to mean the conditional probability of a component or
system performing an intended function given that a specific hurricane surge has occurred. This
result can also be used to determine the conditional probability of failure. System failure refers to
the failure of the HPS to provide protection from flooding in one or more protected areas and can
also be thought of as the occurrence of flood inundation. The effectiveness of the protection
system is also dependent upon how well the operational elements of the system performed.
Elements such as road closure structures, gate operations and pumping plants, etc., that require
human operation and proper installation during a flood fight can dramatically impact flood
levels. The lessons learned concerning the performance of these elements during Katrina was
considered in the analysis.
The changed demographics of the local areas protected by the system were considered when
determining the consequences. In some areas, many homes and much of the infrastructure were
destroyed by the hurricane and some may not be rebuilt. Therefore, the pre-Katrina populations
and property values were impacted and must be considered in the post-Katrina analysis. The
Consequence Team has provided the estimated post-Katrina direct economic damage and
population projections that are used in the risk analysis.
“Risk” is defined as expected losses in terms of lives or dollars generally calculated by combining
the probability of system failure with the consequences associated with that failure. For
New Orleans, the post-Katrina risks were different due to the changing demographics noted
above. In order to better compare the adequacy of the pre- and post-Katrina HPS, probability of
failure and frequency of inundation mapping were used as the primary metrics by which to measure
the effectiveness of repairs and improvements. The inundation mapping, and associated
stage-frequency curves, are intended to be used for estimating the relative risks of flooding
throughout the New Orleans area for the purpose of identifying areas of vulnerability. These
estimates should not be compared to inundation mapping conducted under the Federal
Emergency Management Agency’s (FEMA’s) flood insurance programs since the methods of
analyses, ADCIRC grids, and number of hurricanes modeled are different. The Risk Team has
coordinated with FEMA during the analyses to identify similarities and differences in the
methods of analysis.
Participants
The following individuals actively participated on this project during the period October
2005 through June 2006.
Name
Co-Leads
Agency Role
Jerry L. Foster, P.E. HQUSACE Lead Project Coordinator &
Manager
Bruce Muller, P.E. USBR Asst. Project Coordinator
Headquarters
Donald R. Dressler, P.E HQUSACE Project Sponsor
Volume VIII Engineering and Operational Risk and Reliability Analysis VIII-3
This is a preliminary report subject to revision; it does not contain final conclusions of the United States Army Corps of Engineers.