The following is a direct abstract of the Executive Summary section of the Draft Final Report (“Investigation of the Performance of the New Orleans Flood Protection System in Hurricane Katrina on August 29, 2005”) issued earlier this week by researchers, following an eight-month study of the New Orleans levee system and its performance during Hurricane Katrina. The study, funded by two National Science Foundation (www.nsf.gov) grants, finds that the New Orleans regional flood protection system failed at many locations during Hurricane Katrina, and by many different modes and mechanisms. According to the study, the wide range of problems that produced failures in the levee system calls into question the effectiveness of even those sections that survived Hurricane Katrina.
Ultimately, the study says, “Simply addressing engineering design standards and procedures is unlikely to be sufficient to provide a suitably reliable level of protection.” It recommends, “There is a need to resolve dysfunctional relationships between federal and more local government and the federal and local agencies responsible for the actual design, construction, and maintenance of such flood protection systems. Some of these groups need to enhance their technical capabilities — a long-term expense that would clearly represent a prudent investment at both the national and local level, given the stakes as demonstrated by the losses in this recent event. Steady commitment and reliable funding, shorter design and construction timeframes, clear lines of authority and responsibility, and improved overall coordination of disparate system elements and functions are all needed as well.”
To download the report in its entirety, visit www.ce.berkeley.edu/~new_orleans/.
This report presents the results of an investigation of the performance of the New
Orleans regional flood protection system during and after Hurricane Katrina, which
struck the New Orleans region on August 29, 2005. This event resulted in the single
most costly catastrophic failure of an engineered system in history. Current damage
estimates at the time of this writing are on the order of $100 to $150 billion in the greater
New Orleans area, and the official death count in New Orleans and southern Louisiana at
the time of this writing stands at 1,293, with an additional 306 deaths in nearby southern
Mississippi. An additional approximately 400 people are currently still listed as
“missing”; it is expected that some of these missing were temporarily lost in the shuffle
of the regional evacuation, but some of these are expected to have been carried out into the swamps and the Gulf of Mexico by the storm’s floodwaters, and some are expected to
be recovered in the ongoing sifting through the debris of wrecked homes and businesses,
so the current overall regional death count of 1,599 is expected to continue to rise a bit
further. More than 450,000 people were initially displaced by this catastrophe, and at the
time of this writing more than 200,000 residents of the greater New Orleans metropolitan
area continue to be displaced from their homes by the floodwater damages from this
This investigation has targeted three main questions as follow: (1) What
happened?, (2) Why?, and (3) What types of changes are necessary to prevent recurrence
of a disaster of this scale again in the future?
To address these questions, this investigation has involved: (1) an initial field
reconnaissance, forensic study and data gathering effort performed quickly after the
arrival of Hurricanes Katrina (August 29, 2005) and Rita (September 24, 2005), (2) a
review of the history of the regional flood protection system and its development, (3) a
review of the challenging regional geology, (4) detailed studies of the events during
Hurricanes Katrina and Rita, as well as the causes and mechanisms of the principal
failures, (4) studies of the organizational and institutional issues affecting the
performance of the flood protection system, (5) observations regarding the emergency
repair and ongoing interim levee reconstruction efforts, and (6) development of findings
and preliminary recommendations regarding changes that appear warranted in order to
prevent recurrence of this type of catastrophe in the future.
In the end, it is concluded that many things went wrong with the New Orleans
flood protection system during Hurricane Katrina, and that the resulting catastrophe had
it roots in three main causes: (1) a major natural disaster (the Hurricane itself), (2) the
poor performance of the flood protection system, due to localized engineering failures,
questionable judgements, errors, etc. involved in the detailed design, construction,
operation and maintenance of the system, and (3) more global “organizational” and
institutional problems associated with the governmental and local organizations
responsible for the design, construction, operation, maintenance and funding of the
overall flood protection system.
After eight months of detailed study, a much clearer picture has now emerged
regarding the causes and mechanisms of this catastrophe. Many of the findings of this
study represent a different view of key elements of this event than has been publicly
presented to date.
Hurricane Katrina was a large hurricane, and its arrival at New Orleans
represented the root cause of a natural disaster. This disaster grew to a full blown
catastrophe, however, principally due to the massive and repeated failure of the regional
flood protection system and the consequent flooding of approximately 85% of the greater
metropolitan area of New Orleans.
As Hurricane Katrina initially approached the coast, the resulting storm surge and
waves rose over the levees protecting much of a narrow strip of land on both sides of the
lower Mississippi River extending from the southern edge of New Orleans to the Gulf of
Mexico. Most of this narrow protected zone, Plaquemines Parish, was massively
inundated by the waters of the Gulf.
The eye of the storm next proceeded to the north, on a path that would take it just
slightly to the east of New Orleans.
Hurricane Katrina has been widely reported to have overwhelmed the eastern side
of the New Orleans flood protection system with storm surge and wave loading that
exceeded the levels used for design of the system in that area. That is a true statement,
but it is also an incomplete view. The storm surge and wave loading at the eastern flank
of the New Orleans flood protection system was not vastly greater than design levels, and
the carnage that resulted owed much to the inadequacies of the system as it existed at the
time of Katrina’s arrival. Some overtopping of levees along the eastern flank of the
system (along the northeastern frontage of the St. Bernard and Ninth Ward protected
basin, and at the southeast corner of the New Orleans East protected basin), and also in
central areas (along the GIWW channel and the IHNC channel) was inevitable given the
design levels authorized by Congress and the surge levels produced in these areas by the
actual storm. It does not follow, however, that this overtopping had to result in
catastrophic failures and breaching of major portions of the levees protecting these areas,
nor the ensuing catastrophic flooding of these populous areas.
The northeast flank of the St. Bernard/Ninth Ward basin’s protecting “ring” of
levees and floodwalls was incomplete at the time of Katrina’s arrival. The critical 11
mile long levee section fronting “Lake” Borgne (which is actually a Bay, connected
directly to the Gulf of Mexico) was being constructed in stages, and funding
appropriation for the final stage had long been requested by the U.S. Army Corps of
Engineers (USACE), but this did not arrive before Katrina struck; as a result large
portions of this critical levee frontage were several feet below final design grade. In
addition, an unfortunate decision had been made to use local dredge spoils from the
excavation of the adjacent MRGO channel for construction of major portions of the
levees along this frontage. The result was that major portions of these levees were
comprised of highly erodible sand and lightweight shell sand fill.
When the storm surge arrived, massive portions of these levees eroded
catastrophically and the storm surge passed through this frontage while still on the rise,
crossed an open swamp area that should have safely absorbed most of the overtopping
flow from the outer levees (if they had not catastrophically eroded), and it then crossed
easily over a secondary levee of lesser height that had not been intended to face a storm
surge largely undiminished by the minimal interference of the too rapidly eroded outer
levees fronting Lake Borgne. The resulting carnage in St. Bernard Parish was
devastating, as the storm surge rapidly filled the protected basin to an elevation of
approximately +12 feet above sea level; deeply inundating even neighborhoods with
ground elevations well above sea level in this area.
The storm surge swelled waters of Lake Borgne also passed over and then
through a length of levees at the southeast corner of the New Orleans East protected
basin. Here too, the levees fronting Lake Borgne had been constructed primarily using
materials dredged from the excavation of an adjacent channel (the GIWW channel), and
these levees also contained major volumes of highly erodible sands and lightweight shell
sands. These levees also massively eroded, and produced the principal source of flooding
that eventually inundated the New Orleans East protected area. Here again there was an
area of undeveloped swampland behind the outer levees that might have absorbed the
brunt of any overtopping flow, and a secondary levee of lesser height was in place behind
this swampland that might then have prevented catastrophic flooding of the populous
areas of New Orleans East. This secondary levee was not able to resist the massive flows
resulting from the catastrophic erosion of the highly erodible section of the Lake Borgne
frontage levee, however, and the floodwaters passed over the secondary levee and began
the filling of the New Orleans East protected basin.
The catastrophic erosion of these two critical levee frontages need not have
occurred. These frontages could instead have been constructed using well compacted
clay fill with good resistance to erosion, and they could have been further armored in
anticipation of the storm surge and wave loading from Lake Borgne. The levee at the
northeast edge of St. Bernard Parish could have been completed in a more timely manner.
The result would have been some overtopping, but not catastrophic erosion and
uncontrolled breaching of these critical frontages. Some flooding and damage would
have been expected, but it need not have been catastrophic.
The storm surge swollen waters of Lake Borgne next passed laterally along the
east-west trending GIWW/MRGO channel to its intersection at a “T” with the northsouth
oriented IHNC channel, overtopping levees along both banks to a limited degree.
This produced an additional breach of a composite earthen levee and concrete floodwall
section along the southern edge of New Orleans East, adding additional uncontrolled
inflow to this protected basin. This failure could have been prevented at little
incremental cost if erosion protection (e.g. a concrete splash pad, or similar) had been
emplaced along the back side of the concrete floodwall at the levee crest, but the USACE
felt that this was precluded by Federal rules and regulations regarding authorized levels
The surge next raised the water levels within the IHNC channel, and produced a
number of failures on both the east and west banks. Two major failures occurred on the
east side of the IHNC, at the west edge of the Ninth Ward. Overtopping occurred at both
of these locations, but this was not the principal cause of either of these failures. Both
failures were principally due to underseepage flows that passed beneath the sheetpile
curtains supporting the concrete floodwalls at the crests of the levees. Like many
sections of the flood protection system, these sheetpiles were too shallow to adequately
cut off, and thus reduce, these underseepage flows. The result was two massive breaches
that devastated the adjacent Ninth Ward neighborhood, and then pushed east to meet with
the floodwaters already rapidly approaching from the east from St. Bernard Parish as a
result of the earlier catastrophic erosion of the Lake Borgne frontage levees.
Several additional breaches also occurred farther north on the east side of the
IHNC fronting the west side of New Orleans East, but these were relatively small
features and they just added further to the uncontrolled flows that were now progressively
filling this protected basin. These breaches occurred mainly at junctures between
adjoining, dissimilar levee and floodwall sections, and represented good examples of
widespread failure to adequately engineer these “transitions” between sections of the
regional flood protection system.
Several breaches occurred on the west side of the IHNC, and these represented the
first failures to admit uncontrolled floodwaters into the main metropolitan (downtown)
protected area of New Orleans. These features did not scour and erode a path below sea
level, however, so they admitted floodwaters for a number of hours and then these
inflows ceased as the storm surge in the IHNC eventually subsided. Only 10% to 20% of
the floodwaters that eventually inundated a majority of the main (downtown) New
Orleans protected basin entered through these features.
These failures and breaches on the west side of the IHNC all appear to have been
preventable. One failure was the result of overtopping of an I-wall, with the overtopping
flow then eroding a trench in the earthen levee crest at the inboard side of the floodwall.
This removal of lateral support unbraced the floodwall, and it was pushed over laterally
by the water pressures from the storm surge on the outboard side. Here again the
installation of erosional protection (e.g. concrete splash pads or similar) might have
prevented the failure.
The other failures in this area occurred at “transitions” between disparate levee
and floodwall sections, and/or at sections where unsuitable and highly erodible
lightweight shell sand fills had been used to construct levee embankments. Here, again,
these failures were as much the result of design choices and/or engineering and oversight
issues as the storm surge itself.
As the eye of the hurricane next passed to the northeast of New Orleans, the
counterclockwise swirl of the storm winds produced a storm surge against the southern
edge of Lake Pontchartrain. This produced additional temporary overtopping of a long
section of levee and floodwall at the west end of the lakefront levees of New Orleans
east, behind the old airport, adding further to the flows that were progressively filling this
The surge against the southern edge of Lake Pontchartrain also elevated the water
levels within three drainage canals at the northern edge of the main metropolitan
(downtown) New Orleans protected basin, and this would produce the final, and most
damaging, failures and flooding of the overall event.
The three drainage canals should not have been accessible to the storm surge.
The USACE had tried for many years to obtain authorization to install floodgates at the
north ends of the three drainage canals that could be closed to prevent storm surges from
raising the water levels within the canals. That would have been the superior technical
solution. Dysfunctional interaction between the local Levee Board (who were
responsible for levees and floodwalls, etc.) and the local Water and Sewerage Board
(who were responsible for pumping water from the city via the drainage canals)
prevented the installation of these gates, however, and as a result many miles of the sides
of these three canals had instead to be lined with levees and floodwalls.
The lining of these canals with levees topped with concrete floodwalls was
rendered very challenging due to (a) the difficult local geology of the foundation soils,
and (b) the narrow right of way (or available “footprint”) for these levees. As a result of
the decision not to install the floodgates, the three canals represented potentially
vulnerable “daggers” pointed at the heart of the main metropolitan New Orleans
protected basin. Three major breaches would occur on these canals; two on the London
Avenue Canal and one on the 17th Street Canal. All three of these breaches eroded and
scoured rapidly to well below sea level, and these three major breaches were the source
of approximately 80% of the floodwaters that then flowed into the main (downtown)
protected basin over the next three days, finally equilibrating with the still slightly
elevated waters of Lake Pontchartrain on Thursday, September 1.
The central canal of the three, the Orleans Canal, did not suffer breaching, but a
section of floodwall topping the earthen levee approximately 200 feet in length near the
south end of the canal had been left incomplete, again as a result of dysfunctional
interaction between the local levee board and the water and sewerage board. This
effectively reduced the level of protection for this canal from about +12 to +13 feet above sea level (the height of the tops of the floodwalls lining the many miles of the canal) to an elevation of about +6 to +7 feet above sea level (the height of the earthen levee crest along the 200 foot length where the floodwall that should have topped this levee was omitted). As a result of the missing floodwall section, flow passed through this “hole” and began filling the heart of the main New Orleans protected basin. This flow eventually ceased as the storm surge subsided, and so was locally damaging but not catastrophic.
The three breaches on the 17th Street and London Avenue canals were
catastrophic. None of these failures were the result of overtopping; surge levels in all three drainage canals were well below the design levels, and well below the tops of the floodwalls. Two of these breaches were the result of stability failures of the foundation soils underlying the earthen levees and their floodwalls, and the third was the result of underseepage passing beneath the sheetpile curtain and resultant catastrophic erosion near the inboard toe of the levee that eventually undermined the levee and floodwall.
A large number of engineering errors and poor judgements contributed to these
three catastrophic design failures, as detailed in Chapter 8. In addition, a number of these same problems appear to be somewhat pervasive, and call into question the integrity and reliability of other sections of the flood protection system that did not fail during this event. Indeed, additional levee and floodwall sections appear to have been potentially heading towards failure when they were “saved” by the occurrence of the three large breaches (which rapidly drew down the canal water levels and thus reduced the loading on nearby levee and floodwall sections.)
The New Orleans regional flood protection system failed at many locations during
Hurricane Katrina, and by many different modes and mechanisms. This unacceptable performance was to a large degree the result of more global underlying “organizational” and institutional problems associated with the governmental and local organizations jointly responsible for the design, construction, operation, and maintenance of the flood protection system, including provision of timely funding and other critical resources. Our findings to date indicate that no one group or organization had a monopoly on responsibility for the catastrophic failure of this regional flood protection system. Many groups, organizations and even individuals had a hand in the numerous failures and shortcomings that proved so catastrophic on August 29th. It is a complex situation, without simple answers.
It is not without answers and potential solutions, however, just not simple ones.
There is a need to change the process by which these types of large and critical protective systems are created and maintained. It will not be feasible to provide an assured level of protection for this large metropolitan region without first making significant changes in the organizational structure and interactions of the national and more local governmental bodies and agencies jointly responsible for this effort. Significant changes are also needed in the engineering approaches and procedures used for many aspects of this work, and there is a need for interactive and independent expert technical oversight and review as well. In numerous cases, it appears that such review would have likely caught and challenged errors and poor judgements (both in engineering, and in policy and funding) that led to failures during Hurricane Katrina.
Simply updating engineering procedures and design manuals will not provide the
needed level of assurance of safety of the population and properties of this major
metropolitan region. Design procedures and standards employed for many elements of the flood protection system can be traced back to initial development and use for design and construction of levees intended for protection of largely unpopulated agrarian land, not a major urban region. Design levels of safety and reliability were nowhere near those generally used for major dams; largely because dams are considered to pose a potential risk to large populations. There are few U.S. dams that pose risk to populations as large as the greater New Orleans region, however, and it is one of the recommendations of this study that standards and policies much like those used for “dams” should be adopted for levee systems protecting such regions.
Simply addressing engineering design standards and procedures is unlikely to be
sufficient to provide a suitably reliable level of protection. There is also a need to resolve dysfunctional relationships between federal and more local government and the federal and local agencies responsible for the actual design, construction and maintenance of such flood protection systems. Some of these groups need to enhance their technical capabilities; a long-term expense that would clearly represent a prudent investment at both the national and local level, given the stakes as demonstrated by the losses in this recent event. Steady commitment and reliable funding, shorter design and construction timeframes, clear lines of authority and responsibility, and improved overall coordination of disparate system elements and functions are all needed as well.
And there is some urgency to all of this. The greater New Orleans regional flood
protection system was significantly upgraded in response to flooding produced by
Hurricane Betsy in 1965. The improved flood protection system was intended to be
completed in 2017, fully 52 years after Betsy’s calamitous passage. The system was
incomplete when Katrina arrived. As a nation, we must manage to dedicate the resources necessary to complete projects with such clear and obvious ramifications for public safety in a more timely manner.
New Orleans has now been flooded by hurricanes six times over the past century;
in 1915, 1940, 1947, 1965, 1969 and 2005. It should not be allowed to happen again.