Abstract: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: ͑1͒ the need for regional-scale flood protection systems to perform as systems, with the various components meshing well together in a mutually complementary manner; ͑2͒ the importance of considering all potential failure modes in the engineering design and evaluation of these complex systems; and ͑3͒ 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 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 ͑1͒ the need for realistic assessment of risk exposure as an element of flood protection policy; ͑2͒ the importance of considering erodibility of embankment and foundation soils in levee design and construction; ͑3͒ the importance of considering all potential failure modes; and ͑4͒ 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.

This paper addresses damage caused by Hurricane Katrina to the main Orleans East Bank protected basin. This basin represented the heart of New Orleans, and contained the main downtown area, the historic French Quarter, the Garden District, and the sprawling Lakefront and Canal Districts. Nearly half of the loss of life during this hurricane, and a similar fraction of the overall damages, occurred in this heavily populated basin. There are a number of important geotechnical lessons, as well as geo-forensic lessons, associated with the flooding of this basin. These include the difficulties associated with the creation and operation of regional-scale flood protection systems requiring federal and local cooperation and funding over prolonged periods of time. There are also a number of engineering and policy lessons regarding ͑1͒ the accuracy and reliability of current analytical methods; ͑2͒ the shortcomings and potential dangers involved in decisions that reduced short-term capital outlays in exchange for increased risk of potential system failures; ͑3͒ the difficulties associated with integrating local issues with a flood risk reduction project; and ͑4͒ the need to design and maintain levees as systems; with each of the many individual project elements being required to mesh seamlessly. These lessons are of interest and importance for similar flood protection systems throughout numerous other regions of the United States and the world.