New Orleans and Hurricane Katrina. IV: Orleans East Bank (Metro) Protected Basin

Abstract

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.

New Orleans and Hurricane Katrina. II: The Central Region and the Lower Ninth Ward

“…The mechanism of underseepage-induced uplift and erosional piping failure best fits the narrow geometry of the observed failure ͑and closely matches the similarly narrow geometry of the failure near the south end of the London Avenue Drainage Canal, which was also judged most likely to be an underseepage-induced piping failure; Seed et al 2008b;IPET 2007͒. The available field information and local observations regarding apparent permeability characteristics and the local history of underseepage problems prior to Katrina also lend support for this mechanism.…”

New Orleans and Hurricane Katrina. III: The 17th Street Drainage Canal

“…An incipient failure oc curred on the opposite side �i.e., west bank� of the canal, where levee movements indicate that another failure was developing. This second incident will be discussed along with other geo graphically related events in the fourth companion paper of this series �Seed et al 2008b�. In this paper, the interplay between local geology, history of design, and construction, and the storm surge loading at the east bank breach site are investigated, and the observed response of the levee system is explained.…”

Experimental Study on Subsurface Erosion of Peats

“…The devastating impact of Hurricane Katrina on New Orleans's levees galvanized public awareness of the fragility of California's 13,700-mile levee system. During Hurricane Katrina, three levee breaches were possibly caused by underseepage-induced failure due to piping (Seed et al, 2008a(Seed et al, , 2008bSills et al, 2008). Subsurface erosion has three forms ( Figure 1): (1) heaving or sand boil -the upward movement of soil particles when subjected to a high seepage gradient in the vicinity of the exit flow; (2) piping -soil particles inside the soil matrix are entrained and washed out of the matrix by concentrated seepage, forming a tubular pipe that progresses from downstream to upstream; the pipe can develop into a large tunnel that may collapse; (3) suffusion -the entrainment of fine soil grains and their subsequent deposition in the pores that are formed by coarse grains; suffusion may be caused by discontinuity or segregation of soil particles and it can form large local cavities.…”

“…In the U.S., peat deposits are found in forty-two states and their properties are significantly different from those of inorganic soils (Mesri and Ajlouni, 2007). In two of the major levee breaches in New Orleans during Hurricane Katrina, organic soils were present (Seed et al, 2008a(Seed et al, , 2008bSills et al, 2008). In the Sacramento-San Joaquin Delta, many levees were built upon peat deposits at shallow depth.…”