The failure of the New Orleans regional flood protection systems, and the resultant catastrophic flooding of much of New Orleans during Hurricane Katrina, represents the most costly failure of an engineered system in U.S. history. This paper presents an overview of the principal events that unfolded during this catastrophic hurricane, and then a more detailed look at the early stages of the event as the storm first drove onshore and then began to pass to the east of the main populated areas. The emphasis in this paper is on geotechnical lessons and it also includes broader lessons with regard to the design, implementation, operation, and maintenance of major flood protection systems. This paper focuses principally on the early stages of this disaster, including the initial inundation of Plaquemines Parish along the lower reaches of the Mississippi River as Katrina made landfall, and the subsequent additional early levee breaches and erosion along the eastern flanks of the regional flood protection systems fronting Lake Borgne that resulted in the flooding of the two large protected basins of New Orleans East and St. Bernard Parish. Significant lessons learned include (1) the need for realistic assessment of risk exposure as an element of flood protection policy; (2) the importance of considering erodibility of embankment and foundation soils in levee design and construction; (3) the importance of considering all potential failure modes; and (4) the problems inherent in the construction of major regional systems over extended periods of multiple decades. These are important lessons, as they are applicable to other regional flood protection systems in other areas of the United States, and throughout much of the world.

The failure of the levee and floodwall section on the east bank of the 17th Street drainage canal was one of the most catastrophic breaches that occurred during Hurricane Katrina. It produced a breach that rapidly scoured a flow pathway below sea level, so that after the storm surge had largely subsided, floodwaters still continued to stream in through this breach for the next two and a half days. This particular failure contributed massively to the overall flooding of the Metropolitan Orleans East Bank protected basin. Slightly more than half of the loss of life, and a similar fraction of the overall damages, occurred in this heavily populated basin. There are a number of important geotechnical and geoforensic lessons associated with this failure. Accordingly, this paper is dedicated solely to investigating this single failure. Geological and geotechnical details, such as a thin layer of sensitive clay that was laid down by a previous hurricane, proper strength characterization of soils at and beyond the toe of the levee, and recognition of a water-filled gap on the inboard side of the sheet pile cutoff wall are judged to be among the most critical factors in understanding this failure. The lessons learned from this study are of importance for similar flood protection systems throughout other regions of the United States and the world.

The failure of the New Orleans regional flood protection systems, and the resultant catastrophic flooding of much of New Orleans during Hurricane Katrina, represents the most costly failure of an engineered system in U.S. history. This paper presents an overview of the principal events that unfolded in the central portion of the New Orleans metropolitan region during this hurricane, and addresses the levee failures and breaches that occurred along the east-west trending section of the shared Gulf Intracoastal Waterway/Mississippi River Gulf Outlet channel, and along the Inner Harbor Navigation Channel, that affected the New Orleans East, the St. Bernard Parish, and the Lower Ninth Ward protected basins. The emphasis in this paper is on geotechnical lessons, and also broader lessons with regard to the design, implementation, operation, and maintenance of major flood protection systems. Significant lessons learned here in the central region include: (1) the need for regional-scale flood protection systems to perform as systems, with the various components meshing well together in a mutually complementary manner; (2) the importance of considering all potential failure modes in the engineering design and evaluation of these complex systems; and (3) the problems inherent in the construction of major regional systems over extended periods of multiple decades. These are important lessons, as they are applicable to other regional flood protection systems in other areas of the United States, and throughout much of the world.

The most populous of the four major protected areas that suffered significant flooding during Hurricane Katrina was the main Orleans East Bank (downtown) protected area. Two sets of failures and breaches admitted floodwaters to this region during hurricane Katrina: a series of failures along the Inner Harbor Navigation Channel - IHNC (as discussed in the companion paper), and three major breaches on the drainage canals at the north end of this populous area. The IHNC frontage failures all failed to scour paths consistently below sea level, so flow through these ceased fairly rapidly as the hurricane induced storm surge subsided. The three breaches on the drainage canals, on the other hand, all rapidly scoured to well below sea level. Flow through these thus continued for three days, eventually filling the basin and accounting for approximately half of the overall loss of life and a similar fraction of the overall damages in this catastrophic event. Flow in through these breaches finally equilibrated with the still slightly elevated waters of Lake Borgne on Thursday, September 1. This paper presents a summary of the results of an investigation of the performance of the levees and floodwalls along these three critical drainage canals.

The recent flooding and devastation of the greater New Orleans region during hurricane Katrina represented the most costly peace-time failure of an engineered system in North American history. Extensive investigations and analyses have been performed by several major teams in the wake of this disaster, and some very important lessons have been learned. Many of these have very direct and urgent applications to levee systems in other regions throughout the U.S., and the world. Lessons include the importance of proper evaluation of risk and hazard; so that appropriate decisions can be made regarding the levels of expense and effort that should be directed towards prevention of catastrophe, and the levels of post-disaster response capability that should be maintained as well. The making of appropriate decisions, given this information regarding risk levels, is then also important. Also of vital importance are numerous "engineering" lessons regarding analysis, design, construction and maintenance; hard-won lessons with applications to flood protection systems everywhere. We must now do everything possible to capitalize upon these; and to prevent a recurrence of this type of catastrophe in the future.

The Inner Harbor Navigation Channel (IHNC) sits at the heart of the three main populated regions of New Orleans. As shown in Figure 1, a number of breaches of varying severity occurred along the shores of the IHNC during Hurricane Katrina, contributing to the flooding of all three of the most heavily populated protected areas flooded in this event. This paper presents the results of geotechnical and geo-forensic investigations performed to determine the causes of the various failures along the shorelines of the IHNC. This includes the two massive breaches at the west end of the Lower Ninth Ward, and a number of lesser breaches and partial breaches (distressed sections) along other sections of the canal. There are many lessons here, not just for the greater New Orleans region, but for the nation and for the Profession as well.