Hauling sandbags, 

New Orleans 

U.S. Army photo
275

Why the New Orleans 

Levees Failed

What makes the New Orleans levees unusual is the high stakes involved in 

terms of the population being protected. ... In a system with several hundred 

miles of levees, it is very diffi cult to do suitable investigation and basically to 

nail all the details. ... If you leave one detail unnailed, you leave a vulnerability 

which may in the end bring the whole system down.1

— Raymond Seed, Ph.D., National Science Foundation-sponsored 

Independent Levee Inspection Team (ILIT), University of California, Berkeley

The fl ooding of the metropolitan New Orleans area challenged emergency response 

at all levels. Th is fl ooding was largely caused by failures of the levees and fl oodwalls 

in and around New Orleans. An examination of why the levees failed to protect 

New Orleans is critical,2

 and several teams of scientists of varied affi liation are presently 

conducting massive studies of the mechanisms responsible for the fl ooding. Topics of forensic analysis include:

• Levee breaches along the 17th Street, London Avenue, and the Inner Harbor 

Navigation Canals 

• Overtopping of various levees and fl oodwalls

• Design and construction issues

• Proper levee/fl oodwall oversight

• Subsidence in the metropolitan New Orleans area

• Th e impact of the Mississippi River Gulf Outlet (MRGO)

The Levee Breaches Along the 17th Street and London Avenue Canals

Th ree levee breaches along the major stormwater drainage, or “outfall,” canals of central 

New Orleans – one breach on the east side of the 17th Street Canal and two others along the 

London Avenue Canal (on the east and west) – caused catastrophic fl ooding in the heart of 

the city. Th ese canals are part of the city’s drainage system and allow rain and fl ood waters 

to be pumped out of the city into Lake Pontchartrain.

Breaches in the fl oodwalls along these canals caused water from Lake Pontchartrain to fl ood 

into, among other areas, the Central Business District, the blocks surrounding the Superdome, Lakeview, Mid City, the area around Tulane University, and Lakewood.3

 It was this 

fl ooding that made the humanitarian and rescue eff orts at the Superdome and Convention 

Center so diffi cult.

Scientists have confi rmed that these levee and fl oodwall breaches were unlike the failures 

of levees and fl oodwalls in other areas of the metropolitan New Orleans region, which were 

overtopped by Katrina’s storm surge. Th ere is scientifi c consensus that the fl oodwalls along 

the 17th Street Canal (and the London Avenue Canal) were not, prior to failure, overtopped 

by the storm surge from Lake Pontchartrain.4

 A report by the U.S. Army Corps of Engineers’ Interagency Performance Evaluation Task Force (IPET) – an academically diverse 

group of scientists examining, among numerous other issues, the type of failure in the 17th 

Street Canal breach – gave two causes for the breach.

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276

First, the concrete fl oodwall, which stood 

erect at the crest of the earthen levee and was 

supported by steel sheetpiles driven into, and 

below, the earthen levee, was pushed away 

from the canal by waters rising toward the 

protected land side. As it was pushed away, a 

gap was created between the fl oodwall (along 

with the sheetpile upon which it was supported) and the adjacent levee embankment soils. 

Th is allowed fl ood waters to rush into the 

gap, apply pressure against the lower sheetpiles supporting the fl oodwall underground, 

and push the embankment section aside. 

Once the embankment began to be pushed 

aside, a second failure mechanism combined 

to produce a catastrophic failure of the wall. 

Th is second mechanism was the failure of an 

unusually weak layer of clay at the foundation 

or “toe” of the levee. Under pressure from 

fl oodwaters pressing on the wall, this layer gave way and allowed the “lateral translation,” 

or movement, of the earthen levee supporting the fl oodwall along the “failure plain” in the 

weak clay layer. Th ese combined mechanisms resulted in the violent sideways heave of the 

entire embankment section.5

While the forensic teams generally agree that the 17th Street Canal breach was the result 

of structural failure, they disagree whether the original design anticipated this problem. 

Th e IPET report said that it did not.6

 However, in the National Science Foundation-sponsored Independent Levee Inspection Team’s (ILIT) Initial Comments on Interim (70%) 

IPET Study Report, Raymond B. Seed, Ph.D., and Robert G. Bea, Ph.D., took issue with the 

IPET’s assertion – a concern also raised by the American Society of Civil Engineers External 

Review Panel.7

 Th e ILIT stated that the Corps of Engineers had a “masterful knowledge and 

understanding of the complex and challenging geology of this region in the 1950’s,”8

 and 

“should not claim that the weak foundation soil strata at the 17th Street Canal breach site 

were unexpected, and that no prior publications would have disclosed this possibility.”9

Th e ILIT scientists also referenced a test conducted prior to the construction of the 17th 

Street Canal, which, according to Seed and Bea, foreshadowed the catastrophic failure at the 

breach site. Th ey say a Corps fi eld test of a levee and sheetpile-supported fl oodwall in 1985, 

just south of Morgan City, LA, predicted exactly the sort of failure that occurred at the 17th 

Street Canal. Th e model levee embankment and the sheetpile-supported concrete fl oodwall were sized and built to simulate conditions expected for the 17th Street, Orleans, and 

London Avenue Canals, as well as major portions of the Inner Harbor Navigational Canal. 

“Th us,” the NSF team concluded, “there would seem to be little justifi cation for the contention that the sheetpile failure mode disclosed by the IPET analyses had not previously been 

seen, or published, and that it could not have been anticipated.”10

Th e two breach sites along the London Avenue Canal appear to have been the result of 

foundational instability near the fi ne sand and clay substratum layers at the site.11

Overtopping of Various Levees and Floodwalls

As noted, the fl ooding in the heart of the city was caused by the breaches along the 17th 

Street and London Avenue Canals. But most of the levee and fl oodwall failures in the metropolitan New Orleans area – including New Orleans East, the Lower 9th Ward, St. Bernard 

Breached fl oodwall, New Orleans

Marty Bahamonde photo
Why the New Orleans Levees Failed

277

Parish, and Plaquemines Parish – “were caused by overtopping, as the storm surge rose over 

the tops of the levees and/or their fl oodwalls and produced erosion that subsequently led to 

failures and breaches.”12 One report described the overtopping as follows:

Overtopping was most severe on the east side of the fl ood protection system, 

as the waters of Lake Borgne were driven west towards New Orleans, and also 

farther to the south, along the lower reaches of the Mississippi River. Signifi -

cant overtopping and erosion produced numerous breaches in these areas. Th e 

magnitude of overtopping was less severe along the Inner Harbor Navigation 

Canal (IHNC) and along the western portion of the Mississippi River Gulf 

Outlet (MRGO) channel, but this overtopping again produced erosion and 

caused additional levee failures.13

Finally, as described more fully in the design and construction subsection below, one report 

notes that, “it appears that many of the levees and fl oodwalls that failed due to overtopping 

might have performed better if relatively inexpensive details had been added and/or altered 

during their original design and construction.”14

Design and Construction Issues

Understanding the design and/or construction shortcomings of protective structures is 

critical as the Corps of Engineers proceeds with the rebuilding of the New Orleans region’s 

hurricane protection system.

As one report observes, the protective system is a 

“piecemeal” assemblage of elements that “evolved 

over a long period of time.”15 By contrast, a proper 

system “would integrate components and ... 

would contain a level of redundancy suffi cient 

that, if a levee failed, all would not be lost.”16

For the most part, the reports reviewed by the 

Committee have revealed the following critical 

design and construction issues: (1) I-wall vs. T-wall 

design; (2) vulnerable “transition points” within 

the protective system; (3) accessibility to breach 

sites; and (4) enhanced protection.

I-wall vs. T-wall Design

“I-wall” fl oodwalls run along the top of earthen levees and are supported by metal sheetpiles 

driven into, and below, the earthen levees to various depths. As noted above, the erosion of 

soils on the protected land side of these fl oodwalls was caused by water cascading over the 

tops of the structures themselves, reducing the walls’ resistance to pressure from the water 

side.17 Th is type of failure was “most dramatic” along the Inner Harbor Navigation Canal next 

to the Lower Ninth Ward.”18

Th is type of failure mechanism was not a problem at most T-wall fl oodwalls, which look like 

an inverted “T” and are constructed with concrete bases with more substantial, armored 

foundations.19 Th eir horizontal platforms provide more stability for the vertical wall and 

give the levee soil some protection from water pouring over the top of the wall.

Transition Points

Th e Lake Pontchartrain and Vicinity Hurricane Protection Project (Lake Pontchartrain Project) was authorized in the Flood Control Act of 1965 to provide hurricane protection to areas 

around Lake Pontchartrain in Orleans, Jeff erson, St. Bernard, and St. Charles Parishes.20 Th e 

Ripped-out sheetpile with chunks of 

fl oodwall attached, New Orleans

Louisiana National Guard photo
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278

total project called for the design and construction of approximately 125 miles of levees and 

fl oodwalls.21 Parts of the system were built at diff erent times and involved the review and cooperation of diff erent local levee districts. Quite oft en, this resulted in non-uniform junctions. 

Scientists examining these “transition points” found inconsistencies in crest heights, types of 

protective structures, and materials used.22 In some places, fl oodwalls stood at a higher elevation than adjoining earthen levees, which concentrated the fl ow of water to the non-uniform 

intersection, “causing turbulence that resulted in erosion of the weaker levee soil.”23

One report noted that the key to the transition-points problem is that “infrastructure elements [were being] designed and maintained by multiple authorities.”24 Th e report said the 

result is that “the weakest (or lowest) segment or element controls the overall performance” 

of the hurricane protection system.25 One engineering recommendation was that crest 

heights – the highest elevations of the structure being used, regardless whether it is just a 

levee or a fl oodwall standing upon a levee – should be planned to guide overtopping waters 

“preferentially” toward locations that would minimize damage.26

Accessibility to Breach Sites

Scientists also found that the design of the levees and fl oodwalls along the major outfall 

canals (the 17th Street and London Avenue Canals) hampered emergency operations at the 

breach sites, despite a Corps of Engineers regulation27 about the importance of access roads 

to levees for inspection, maintenance, and fl ood-fi ghting. Th ese narrow access roads usually 

run along the crown of the earthen levee itself. However, the report noted that adding Iwalls to levees in highly built-up areas of New Orleans had sacrifi ced road access to the tops 

of the levees. Th ese decisions resulted in very signifi cant increases in time and cost when it 

became necessary to close breaches along these canals.28 Emergency roads needed to be constructed to get access to the breached areas so that construction equipment and fi ll materials 

could be brought in.

Enhanced Protection

Hurricane Katrina was a catastrophic storm that exceeded the design limits of parts of the 

levee system. Nevertheless, some portion of the fl ooding that occurred could have been lessened had the levees themselves not been eroded – and ultimately breached – by overtopping. 

Th e scientifi c community has determined that the hurricane protection system designed to 

protect the people living within the metropolitan New Orleans area could have (and should 

have) been constructed with enhanced protective features. As noted in one report:

A fundamental fl aw in the fl oodwalls and levees is that they include no means 

of accommodating overtopping that does not infl ict major damage or destruction. ... Most of the 350 miles of levees in New Orleans are unprotected from 

devastating damage and potentially total destruction if overtopped.

Th e question is not whether the levees will again be overtopped but when and 

by how much they will be overtopped.29

Another report found that the performance of many levees and fl oodwalls could have 

been greatly improved “and some of the failures likely prevented, with relatively inexpensive modifi cations” of the system, such as riprap (a loose assemblage of broken stones and 

concrete), concrete splash slabs, or pavement on the protected side of the levees to guard 

against anticipated overtopping.30

Th e failure of the system’s design to adequately address the impact of signifi cant overtopping likely resulted in a system more prone to failure in a major hurricane and should have 

raised greater concern about the eff ects of overtopping.
Why the New Orleans Levees Failed

279

Proper Hurricane Protection System Oversight

As alluded to in the “transition points” subsection above, scientists have noted that there are 

design/technical problems with the hurricane protection system that they attribute to numerous “infrastructure elements [being] designed and maintained by multiple authorities.”31

As Seed testifi ed before the Committee during a public hearing:

No one is in charge. You have got multiple agencies, multiple organizations, 

some of whom aren’t on speaking terms with each other, sharing responsibilities for public safety. Th e Corps of Engineers had asked to put fl ood gates into 

the three canals [structures that would, upon activation, block the waters of Lake 

Pontchartrain from entering the drainage canals], which nominally might have 

mitigated and prevented the three main breaches that did so much destruction 

downtown. But they weren’t able to do that because, unique to New Orleans, the 

Reclamation Districts who were responsible for maintaining the levees are separate from the Water and Sewage District, which does the pumping. Ordinarily, 

the Reclamation District does the dewatering pumping, which is separate from 

the water system. Th ese guys don’t get along. Th e Sewage District was so concerned they wouldn’t be able to pump through gates which had to be opened and 

closed that in the end, the Corps, against its desires, was forced instead to line the 

canals [with the fl oodwalls], which they did with some umbrage, and the locals 

bore a higher than typical fraction of the shared cost as a result of that ...

Levees in the New Orleans area are at diff erent heights. You can stand – we have 

a photograph in our report at one section where you can clearly see fi ve diff erent 

elevations, all within 100 yards of each other. If you have got fi ve diff erent elevations within 100 yards, the person who built the lowest section wins because they 

become the public hazard. Th ere is a need to coordinate these things.32

As a report by the ASCE’s External Review Panel (ERP) notes:

Th e ERP sees clearly that organizational complexities and the ways in which 

decisions are made are among the most important factors that infl uenced the 

performance of the hurricane protection system. Organizational eff ectiveness 

has been and will continue to be questioned, with justifi cation. It is impossible 

for the ERP to conceive a mechanism through which the levee system can be 

rebuilt and operated eff ectively and effi ciently with such organizational discontinuity and chaos.33

Subsidence in the Metropolitan New Orleans Area

In addition to design and construction issues, soil subsidence – “the lowering or sinking 

of [the] earth’s surface”34 – has impaired the protection off ered by the New Orleans levee 

system. In the New Orleans area, subsidence is caused primarily by the cumulative weight 

of millions of years of soil and silt deposits left by the Mississippi River as it enters the Gulf 

of Mexico. Th e sediment literally presses down on the earth’s crust, causing the land to 

sink. As a result, the water level rises, gradually increasing vulnerability to tides and storms. 

Th e levees themselves can also subside because of their own weight pressing down on the 

swampy soils upon which they are built.

As a result, it appears that the level of protection actually provided by the New Orleans 

region’s levee system at the time of Katrina was signifi cantly lower than intended:

Many sections of the levees and fl oodwalls were substantially below their 

original design elevations, an eff ective loss of protection. For example, the 
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280

structures associated with the Inner 

Harbor Navigation Canal were originally 

constructed to an elevation of 15 feet 

(relative to mean sea level) but are now 

just over 12 feet, a typical loss of approximately 2.7 feet in elevation over the 

lifetime of the project.35

Th e report noted that “subsidence is occurring 

at a rate of up to one inch every three years” in 

the New Orleans region.36

Subsidence routinely creates problems for 

those trying to construct levees and other 

structures at known heights above sea level. As 

stated in one IPET report, due to the complex 

and variable subsidence in southeast Louisiana, 

“establishing an accurate vertical reference 

for measurements has been a constant challenge.”37 Unfortunately, until the October 2005 

release by the U.S. Department of Commerce’s 

National Geodetic Survey of 85 benchmarks 

located in southern Louisiana, which showed 

heights (elevations) accurate to between 2 and 

5 centimeters (roughly 1 to 2 inches), surveyors, engineers, and the U.S. Army Corps of 

Engineers in New Orleans evaluated the levees 

and structures built and in use against vertical heights that had not been calibrated nor 

checked for several years.38

As a result, it appears that the levees were not 

built and maintained at the proper level above 

sea level. Since the level of protection that the 

levees provide is so closely related to their 

height above sea level, which aff ects their ability to block increased water levels driven by 

hurricanes, the failure to build and maintain the levees at the proper elevation diminished 

the level of protection they provided.

1 Testimony of Raymond Seed, Ph.D., National Science Foundation, before the U.S. Senate, Committee on Homeland 

Security and Governmental Aff airs, hearing on Hurricane Katrina: Why Did the Levees Fail?, Nov. 2, 2005.

2 Th is section analyzes and summarizes the following scientifi c reports: Th e November 2, 2005, American Society of 

Civil Engineers (ASCE) and National Science Foundation (NSF) Preliminary Report on the Performance of the New 

Orleans Levee System in Hurricane Katrina on August 29, 2005, [hereinaft er, “ASCE/NSF Preliminary Report”]; Th e December 5, 2005, Summary of Field Observations Relevant to Flood Protection in New Orleans, LA: Interim Report to Task 

Force Guardian by the Interagency Performance Evaluation Task Force [hereinaft er, “IPET Summary of Field Observations”]; Th e January 10, 2006, Interagency Performance Evaluation Task Force Performance Evaluation Plan and Interim 

Status, Report 1 of a Series: Performance Evaluation of the New Orleans and Southeast Louisiana Hurricane Protection 

System [hereinaft er, “IPET Report 1 of a Series”]; Th e February 20, 2006, American Society of Civil Engineers External 

Review Panel Progress: Report Number 1 [hereinaft er, “ASCE ERP Progress Report Number 1”]; Th e March 10, 2006, 

Interagency Performance Evaluation Task Force Performance Evaluation, Status and Interim Results, Report 2 of a Series: 

Performance Evaluation of the New Orleans and Southeast Louisiana Hurricane Protection System [hereinaft er, “IPET

Report 2 of a Series”]; and various other ASCE and NSF preliminary evaluations of the IPET Report 2 of a Series.

Plugging a breached fl oodwall, 

New Orleans 

Photo © 2005 The Times-Picayune Publishing 

Co., all rights reserved. Used with permission 

of the Times-Picayune
Why the New Orleans Levees Failed

281

For background, it should be understood that the U.S. Army Corps of Engineers (USACE) responded to Hurricane 

Katrina with, among other things, the activation of Task Force Guardian (TFG), with the crucial responsibility of repairing the damages to the hurricane protective system by the storm. Source: U.S. Army Corps of Engineers, Interagency 

Performance Evaluation Task Force, Summary of Field Observations Relevant to Flood Protection in New Orleans, LA,” 

Dec. 5, 2005, p. 2 [hereinaft er IPET, Summary of Field Operations]. In addition, the Interagency Performance Evaluation 

Task Force (IPET) was established on October 10, 2005, by the Chief of Engineers of the USACE, and sanctioned by the 

Secretary of Defense in a directive to the Secretary of the Army on October 19, 2005. Source: U.S. Army Corps of Engineers, Interagency Performance Evaluation Task Force, Performance Evaluation Plan and Interim Status, Report 1 of a 

Series, Jan. 10, 2006, p. 3 [hereinaft er IPET, Report 1 of a Series]. Th e IPET, “comprised of leading experts in a comprehensive array of science and engineering disciplines [is] charged with studying the response of the hurricane protection 

system during Katrina for lessons learned.” Source: IPET, Summary of Field Observations, p. 2. Moreover, the IPET is 

to “provide credible and objective scientifi c and engineering answers to fundamental questions about the performance 

of the hurricane protection and fl ood damage reduction system in the New Orleans metropolitan area.” Source: IPET,

Report 1 of a Series, p. 3. Th e American Society of Civil Engineers (ASCE) External Review Panel (ERP) then “provide[s] 

for an external, expert, and constructive technical review of the activities and products of the [IPET].” Source: IPET, Report 1 of a Series, Appendix D, p. D–7. While this review is to be comprehensive, and done on a periodic basis, it is clear 

that the “ERP has no approval authority on the fi ndings of the [IPET], nor are the ERP’s recommendations to the [IPET] 

binding, but the [IPET] will give serious consideration to each.” Source: IPET, Report 1 of a Series, Appendix D, p. D–8.

On Nov. 2, 2005, the Committee held a public hearing entitled, “Hurricane Katrina: Why Did the Levees Fail?” [hereinaft er, “HSGAC Levee 1 Hearing”]. Th e witnesses for this hearing were representatives and/or heads of several diff erent 

forensic data gathering teams investigating why the levees in and around New Orleans failed. Testifying before the 

Committee were Raymond B. Seed, Ph.D., on behalf of the National Science Foundation (NSF), Peter Nicholson, 

Ph.D., P.E., on behalf of the ASCE, Ivor van Heerden, Ph.D., of the LSU Hurricane Center and on behalf of the State 

of Louisiana Forensic Data Gathering Team, and Paul F. Mlakar, Ph.D., P.E., on behalf of the USACE. Th e bulk of 

Seed and Nicholson’s formal written testimony provided for the HSGAC Levee 1 Hearing summarized the ASCE/NSF 

Preliminary Report.

During the HSGAC Levee 1 Hearing, Mlakar specifi cally noted the IPET objective: “Th e fi nal results will include conclusions as to the causes of the failures and recommendations for the future design and construction of such infrastructure 

nationwide. Th ese results will be independently reviewed by an external panel of the [ASCE]. At the request of the Secretary of Defense, the National Academies will also independently assess the results and report to the Assistant Secretary of 

the Army for Civil Works.” Source: Testimony of Paul Mlakar, Senior Research Scientist, Army Engineer Research and 

Development Center, before the U.S. Senate, Committee on Homeland Security and Governmental Aff airs, hearing on 

Hurricane Katrina: Why did the Levees Fail?, Nov. 2, 2005.

On Nov. 2, 2005 – the day of the HSGAC Levee 1 Hearing – the ASCE and NSF teams jointly released the ASCE/NSF 

Preliminary Report. As noted in the report itself, the “ASCE/NSF Preliminary Report” present[ed] the results of fi eld 

investigations performed by collaborating teams of scientists and engineers in the wake of the passage of Hurricane Katrina, to study performance of the regional fl ood protection systems and the resulting fl ooding that occurred in the New 

Orleans area.” Source: American Society of Civil Engineers and National Science Foundation, Preliminary Report on the 

Performance of the New Orleans Levee System in Hurricane Katrina on Aug. 29, 2005, Nov. 2, 2005, p. 1–1 [hereinaft er, 

ASCE/NSF, Preliminary Report]. Th e initial fi eld investigations conducted in preparation for the report took place from 

Sept. 28, through Oct. 15, 2005. Source: ASCE/NSF, Preliminary Report, p. iv. Following the ASCE/NSF Preliminary 

Report, on Dec. 5, 2005, the IPET Summary of Field Observations was issued, which consisted of an “IPET review provided [to] Task Force Guardian with a simple statement of concurrence or nonoccurrence from the IPET fl oodwall and 

levee sub team and additional relevant discussion for each of the major fi ndings of the ASCE/NSF “Preliminary Report.” 

Source: IPET, Report 1 of a Series, Appendix F, p. F–2.

Consistent with IPET’s mission, it produced its fi rst evaluation of the metropolitan New Orleans area hurricane protection system on Jan. 10, 2006. Th e IPET Report 1 of a Series is a massive document. Moreover, as noted in its “Purpose” 

section, “IPET, Report 1 of a Series provides a strategic overview of the IPET, the fi nal IPET Scopes of Work on a taskby-task basis, including changes resulting from the review of the [ASCE ERP], and a status report on the work accomplished to date.” Source: IPET, Report 1 of a Series, p. 4. However, and as noted by the Feb. 20, 2006, ASCE ERP Progress 

Report Number 1, “the IPET [Report 1 of a Series] presented no specifi c fi ndings and conclusions, which is not surprising 

in view of the many questions that as yet are unanswered.” Source: American Society of Civil Engineers, letter to Lt. Gen. 

Carl Strock, “ERP Progress Report Number 1,” Feb. 20, 2006, p. 2. Provided to the Committee [hereinaft er ASCE, “ERP 

Progress Report Number 1”]. Th e IPET Final Report “will include the completed analyses for consequences and risk and 

reliability,” and is scheduled for release on June 1, 2006. Source: IPET, Report 1 of a Series, viii.

According to the IPET Report 1 of a Series, Objectives section, the IPET’s overall review is focused on answering the following critical questions:

a. Th e Flood Protection System: What were the design criteria for the pre-Katrina hurricane protection system, and did the design, as-built construction, and maintained condition meet these criteria? 

(1) What were the design assumptions and as-built characteristics of the primary components of the 

fl ood protection system? (2) What records of inspection and maintenance of original construction 

and post-Katrina repairs are available that documents their conditions? (3) What subsurface exploration and geotechnical laboratory testing information was available as the basis of design, and were 

these conditions verifi ed during construction? (4) Were the subsurface conditions at the locations of 

levee failures unique, or are these same conditions found elsewhere?
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282

b. Th e Storm: What were the storm surges and waves used as the basis of design, and how do these 

compare to the storm surges and waves generated by Hurricane Katrina? (1) What forces, as a function of location and time, were exerted against the hurricane protection system by Katrina?

c. Th e Performance: How did the fl oodwalls, levees, pumping stations, and drainage canals, individually and acting as an integrated system, perform in response to Hurricane Katrina, and why? (1) What 

were the primary failure mechanisms and factors leading to failure for those structures suff ering 

catastrophic failure during the storm? (2) What characteristics allowed components of the system to 

perform well under exceptional loads and forces? (3) What was the contribution of the pumping stations and drainage system in the unwatering of fl ooded areas? (4) What areas or components of the 

fl ood protection system have sustained damages that reduce their protection capacity and may need 

some reconstitution of capacity?

d. Th e Consequences: What have been the societal-related consequences of the Katrina-related damage? (1) How are local consequences related to the performance of individual components of the 

fl ood protection system? (2) What would the consequences have been if the system would not have 

suff ered catastrophic failure? (3) What are the consequences of Katrina that extend beyond New 

Orleans and vicinity?

e. Th e Risk: Following the immediate repairs, what will be the quantifi able risk to New Orleans and 

vicinity from future hurricanes and tropical storms? (1) What was the risk to New Orleans and vicinity from hurricanes prior to Katrina? (2) On June 1, 2006, what will be the condition and engineering 

integrity of the New Orleans hurricane protection system, including structural repairs? Source: IPET, 

Report 1 of a Series, p. 6–7.

While all of these questions are important ones – many of which are addressed throughout the balance of this Committee’s 

Report, the following have a direct bearing upon this section of the Committee’s Report: questions (a) and (a)(1)-(4); (b) 

and (b)(1); and (c) and (c)(1)-(2). In any event, given the state of the IPET’s review at the time of this Committee’s Report, 

the IPET Report 1 of a Series can best be used to demonstrate what the DOD sanctioned team of scientists is doing (or plans 

to do), while also taking note of what it is not doing (as referenced in the ASCE ERP Progress Report Number 1).

As noted above, the IPET Final Report is scheduled for release on June 1, 2006. Overall, and as largely recognized by the 

ASCE ERP, the IPET’s goal (and its approach to meeting this goal) is a critical and comprehensive one. Th e IPET Final 

Report has the makings to be – if conducted as planned, including the duo-layered review process – the defi nitive work 

on the lingering scientifi c/forensic questions related to Hurricane Katrina. However, and as referenced elsewhere in 

this Committee’s Report, the organizational problems referenced in the ASCE ERP Progress Report Number 1, and also 

by the scientists who testifi ed before the Committee at the HSGAC Levee 1 Hearing, are signifi cant issues that must be 

properly addressed before residents of the greater New Orleans area are to exude confi dence in the hurricane protection 

system charged with protecting their lives and livelihoods.

3 Ivor L. van Heerden, G. Paul Kemp, Wes Shrum, Ezra Boyd and Hassan Mashriqui, Louisiana State University, Center 

for the Study of Public Health Impacts of Hurricanes, Initial Assessment of the New Orleans’ Flooding Event during the 

Passage of Hurricane Katrina, pp. 7-10. [hereinaft er LSU, Initial Assessment of New Orleans Flooding]. Th e LSU professors also noted that, “[w]ater poured through the three deep breaches of the drainage canals into the New Orleans Metro 

bowl for more than 60 hours, until early Th ursday morning, when the level inside reached equilibrium with the water in 

the lake at about 3 feet above sea level, and with the ‘average’ home in the fl ooded neighborhoods standing in six to nine 

feet of water.” LSU, Initial Assessment of New Orleans Flooding, p. 10.

4 ASCE/NSF Preliminary Report, pp. iv-v, 2–3, 8–2; IPET, Summary of Field Observations, p. 8; and IPET, Report 1 of a 

Series, pp. 113-114; U.S. Army Corps of Engineers, Interagency Performance Evaluation Task Force, Performance Evaluation Plan and Interim Status, Report 2 of a Series, Mar. 10, 2006, p. vi-3 [hereinaft er IPET, Report 2 of a Series].

5 IPET, Report 2 of a Series, p. I–4. See also: Raymond B. Seed and Robert G. Bea, National Science Foundation-Sponsored Independent Levee Inspection Team (ILIT), Univ. of Calif. at Berkeley, Initial Comments on Interim (70%) IPET 

Study Report, Mar. 12, 2006, p. 1 [hereinaft er, ILIT, Initial Comments on Interim (70%) IPET Study Report]. It should be 

noted that the ASCE ERP, noted above, seems to be satisfi ed with the IPET’s assessment: “In its initial review of the U.S. 

Army Corps of Engineers’ [IPET] second report, Status and Interim Results, the [ASCE] External Review Panel (ERP) 

members are generally satisfi ed with the group’s analysis and progress. More specifi cally, we have been impressed with 

the IPET’s investigation of the 17th Street failure mechanism.” American Society of Civil Engineers, “Statement attributable to David Daniel, Ph.D., P.E., president of the University of Texas, Dallas, Chair, American Society of Civil Engineers 

(ASCE) External Review Panel (ERP),” news release, Mar. 10, 2006, p. 1.

6 IPET, Report 2 of a Series, p. I–4 (emphasis added).

7 American Society of Civil Engineers, letter to Lt. Gen. Carl Strock, Mar. 23, 2006, pp. 1-2. Provided to the Committee. Wherein the ASCE ERP also noted the Corps’ knowledge regarding soil/foundational issues in the area of the major 

outfall canals, and the fl oodwall fi eld test demonstrating similar failure mechanisms as that actually realized at the site of 

the 17th Street Canal and referenced in the IPET Report 2 of a Series.

8 ILIT, Initial Comments on Interim (70%) IPET Study Report, p. 1.

9 ILIT, Initial Comments on Interim (70%) IPET Study Report, p. 1.

10 ILIT, Initial Comments on Interim (70%) IPET Study Report, p. 3. See also: American Society of Civil Engineers, Letter to Lt. Gen. Carl Strock, Mar. 23, 2006.
Why the New Orleans Levees Failed

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11 IPET, Report 1 of a Series, p. 106.

12 At this point, it should be noted that the IPET team undertook an analysis to determine the eff ects of the Mississippi River Gulf Outlet (MRGO) upon the storm surge generated by Hurricane Katrina. Th e note, which examined “the 

impact of the MRGO on large scale catastrophic storm surge development and propagation,” found as follows:

Th e MRGO is a dredged channel that extends southeast to northwest from the Gulf of Mexico to a point 

where it fi rst merges with the Gulf Intracoastal Waterway (GIWW), and then continues westward until 

it intersects the Inner Harbor Navigation Canal (IHNC). ... Th e fi rst 9 miles, the bar channel, are in the 

open Gulf. Th e next 23 miles of the channel lie in the shallow open waters of Breton Sound. From there, 

the inland cut extends 14 miles to the northwest with open marsh on the northeast and a 4,000-ft wide 

dredged material placement bank on the southwest side. At this point the channel cuts across the ridge of 

a relict distributary of the Mississippi River, Bayou La Loutre. For nearly the next 24 miles, there is a hurricane protection levee atop a dredged material placement bank on the southwest side of the channel and 

Lake Borgne and open marsh lie to the northeast. A portion of the levee protecting St. Bernard Parish/

Chalmette and the portion of the hurricane protection levee along the south side of Orleans East Parish, 

north of the GIWW, form the “funnel” that is oft en referenced. Th e point where the MRGO and GIWW 

channels merge is just to the east of the Paris Road Bridge. ... From this point, the merged GIWW/

MRGO channel continues west for about 6 miles to the point where it intersects the IHNC; this portion 

has hurricane protection levees on both banks. Th e IHNC extends from Lake Pontchartrain, to the north, 

to the Mississippi River to the south. Th e IHNC has levees or fl oodwalls along both banks. ... Th e MRGO 

bar channel authorized depth is 38 ft ; the authorized bottom width is 600 ft . Th e remainder of the channel 

has an authorized depth of 36 ft and an authorized bottom width of 400 or 450 ft , depending on location.

It is important to distinguish between two sections of the MRGO and the role each plays in tide and 

storm surge propagation. One is the east-west oriented section that runs between the IHNC and the 

confl uence of the GIWW/MRGO near the Paris Road Bridge ... and hereinaft er referred to as Reach 

1. Th e other is the much longer southeast-northwest section ... hereinaft er referred to as the Reach 2. 

IPET, Report 2 of a Series, Appendix E, p. E–2.

Citing past studies, and analyses of their own, the IPET report noted the following regarding MRGO/Reach 2:

Th e change in storm surge induced by MRGO/Reach 2 (computed as a percentage of the peak surge 

magnitude) is greatest when the amplitude of the storm surge is low, on the order of a few feet or less. 

In these situations, changes induced by the MRGO are rather small, 0.5 ft or less, but this amount is 

as much as 25% of the peak surge amplitude. When the long wave amplitude is very low, the surge is 

more limited to propagation via the channels. Once the surge amplitude increases to the point where 

the wetlands become inundated, this section of the MRGO plays a diminished role in infl uencing the 

amplitude of storm surge that reaches the vicinity of metropolitan New Orleans. For storm surges of 

the magnitude produced by Hurricane Betsy and Katrina, which overwhelmed the wetland system, the 

infl uence of MRGO/Reach 2 on storm surge propagation is rather small. When the expansive wetland 

is inundated, the storm surge propagates primarily through the water column over this much larger 

fl ooded area, and the channels become a much smaller contributor to water conveyance. Source: IPET, 

Report 2 of a Series, Appendix E, p. E–4. ... Th e reasons for the very limited infl uence of the MRGO/

Reach 2 in the vicinity of New Orleans for strong storm events are clear. First, the MRGO does not 

infl uence the important preliminary east-west movement of water that drives the signifi cant build up of 

surge in the early parts of the storm. Second, the northerly propagation of surge during the later stages 

of the storm are only minimally infl uenced by the MRGO because the increased hydraulic conveyance 

associated with the channel is very limited for large storms due to the large surge magnitude and especially due to the very large lateral extent of the high waters on the Mississippi-Alabama shelf that build 

up early on from the east. In addition, the propagation direction of this surge wave does not typically 

align with the MRGO and furthermore the southeasterly winds which align with the MRGO occur only 

very briefl y. Source: IPET, Report 2 of a Series, Appendix E, p. E–6.

Finally, the report said of MRGO/Reach 1:

While the simulations clearly show that Reach 2 of the MRGO does not signifi cantly infl uence the 

development of storm surge in the region for large storm events, Reach 1 (the combined GIWW/

MRGO section) and the IHNC, together, provide a hydraulic connection between Lake Borgne and 

Lake Pontchartrain. As a result of this connection, the storm surge experienced within the IHNC and 

Reach 1 (GIWW/MRGO) is a function of storm surge in both Lakes; a water level gradient is established within the IHNC and Reach 1 that is dictated by the surge levels in the two lakes. Th is is true for 

both low and high storm surge conditions. To prevent storm surge in Lake Borgne from reaching the 

IHNC or GIWW/MRGO sections of waterway, fl ow through the Reach 1 channel must be dramatically 

reduced or eliminated, either by a permanent closure or some type of structure that temporarily serves 

to eliminate this hydraulic connectivity. Th e presence of an open channel is the key factor.

Th e hurricane protection levees along the south side of Orleans Parish [Orleans East] and the eastern 

side of St. Bernard Parish along the MRGO, which together are referred to as a funnel, can locally 

collect and focus storm surge in this vicinity depending on wind speed and direction. Th is localized 

focusing eff ect can lead to a small local increase in surge amplitude. Strong winds from the east tend to 

maximize the local funneling eff ect. Source: IPET, Report 2 of a Series, Appendix E, p. E–7.
Chapter 17

284

A team of scientists from LSU, however, seem to take a diff erent position on the MRGO channel. In a report entitled, 

LSU, Initial Assessment of New Orleans Flooding, Ivor L. van Heerden, G. Paul Kemp, Wes Shrum, Ezra Boyd and Hassan Mashriqui state the following:

As the eye of the storm approached the latitude of New Orleans, a 14-17 foot surge was pushed into 

the western apex of a triangle known as the “Funnel”, so called because the hurricane protection levees 

that form the south bank of the MRGO and the north bank of the GIWW converge from being about 

10 miles apart to a few hundred yards at the banks of the GIWW where it separates the East Orleans 

and St. Bernard basins. Th e Funnel is a 6-mile long section of the GIWW where the cross-section was 

enlarged by a factor of three when the MRGO was built to expand it from a barge channel to accommodate ocean-going vessels. At the western end, the Funnel focused a jet into the IHNC. Th e US Army 

Corps of Engineers had inadvertently designed an excellent storm surge delivery system – nothing less 

– to bring this mass of water with simply tremendous “load” – potential energy – right into the middle 

of New Orleans. Source: LSU, Initial Assessment of New Orleans Flooding, p. 4.

13 ASCE/NSF, Preliminary Report, pp. iv-v.

14 ASCE/NSF, Preliminary Report, pp. iv-v.

15 ASCE, “ERP Progress Report Number 1,” p. 3.

16 ASCE, “ERP Progress Report Number 1,” p. 3.

17 ASCE/NSF, Preliminary Report, p. 8–1. See also: IPET, Summary of Field Observations, p. 6.

18 IPET, Summary of Field Observations, p. 6.

19 ASCE/NSF, Preliminary Report, p. 8–1. However, it should be noted that while the IPET report concurred with the 

ASCE/NSF Preliminary Report fi nding regarding the T-walls, noting that, “if overtopping of T-walls did occur, it did not 

lead to extensive scour and erosion,” the IPET team also stated that there were some T-wall structures “that had signifi -

cant scour, but none showed evidence of distress or movement” IPET, Summary of Field Observations, p. 6.

20 Written Statement of Anu Mittal, Director, Natural Resources and Environment, U.S. General Accountability Offi ce, 

for the U.S. Senate on Environment and Public Works, hearing on Comprehensive and Integrated Approach to Meet the 

Water Resources Needs in the Wake of Hurricanes Katrina and Rita, Nov. 9, 2005, p. 2. 

21 Written Statement of Mittal, Senate Committee on Environment and Public Works hearing, Nov. 9, 2005, p. i.

22 ASCE/NSF, Preliminary Report, pp. 8–1 through 8–2; see also IPET, Summary of Field Observations, pp. 6-7; IPET, 

Report 1 of a Series, p. 114.

23 IPET, Summary of Field Observations, pp. 6-7.

24 ASCE/NSF, Preliminary Report, pp. 8–1 through 8–2.

25 ASCE/NSF Preliminary Report, pp. 8–1 through 8–2.

26 ASCE/NSF Preliminary Report, p. 8–3. It should be noted that the IPET team generally agreed with these ASCE/NSF 

comments, however, while the IPET recognized that planning for overtopping by adjusting crest heights “should be 

considered,” the team stated that there are a number of uncertainties regarding the location and size of these planned 

“spillways.” IPET, Summary of Field Observations, p. 11.

27 U.S. Army Corps of Engineers, Engineering and Design, Design and Construction of Levees, Apr. 30, 2000, Section 8–9.

28 ASCE/NSF, Preliminary Report, pp. 8–3 through 8–4. It should also be noted that the IPET team concurred, specifi -

cally noting that, “Given the logistical diffi culties in accessing and sealing the breaches to unwater fl ooded areas, [TFG] 

should carefully reconsider the guidance of EM 1110-2-1913, Section 8-9 [the Army Corps regulation on point].” IPET,

Summary of Field Observations, p. 11.

29 ASCE, “ERP Progress Report Number 1,” p. 3.

30 ASCE/NSF, Preliminary Report, p. 8–3. See also: IPET, Summary of Field Observations, p. 10.

31 ASCE/NSF, Preliminary Report, pp. 8–1 through 8–2. Th e IPET team, however, has left “the issues of organizational 

and jurisdictional complexities that can impact the eff ectiveness of the physical system” to be treated separately. IPET,

Report 2 of a Series, p. I–1.

32 Testimony of Raymond Seed, Ph.D., Team Leader, National Science Foundation, before the U.S. Senate, Committee 

on Homeland Security and Governmental Aff airs, hearing on Hurricane Katrina: Why Did the Levees Fail?, Nov. 2, 2005.

33 ASCE, “ERP Progress Report Number 1,” p. 2.

34 IPET, Report 2 of a Series, p. III–6.

35 IPET, Report 2 of a Series, p. I–2.

36 IPET, Report 2 of a Series, p. III–6.

37 IPET, Report 2 of a Series, p. I–2.

38 IPET, Report 2 of a Series, p. III-6. Signifi cantly, the report found that geodetic elevations are very time-dependant 

in the New Orleans area “and must be periodically adjusted to account for apparent sea level changes.” It also recommended annual reviews to measure subsidence. IPET, Report 2 of a Series, p. III–53.
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