Presented May 22, 2006 in New Orleans
Funded by the National Science Foundation
Highlights compiled by Levees.Org
Levees and floodwalls are constructed to form rings that protect various areas of the Metropolitan New Orleans Area. The Berkeley/NSF report focuses upon three of these protected basins areas that were catastrophically flooded.
St Bernard and the Lower Ninth Ward Basin
St. Bernard Parish and the Lower Ninth Ward in Orleans Parish are protected by a single levee ring. The U.S. Army Corp of Engineers had previously claimed that this area flooded due to massive and unpreventable overtopping of the levees. The Report contradicts the Corps’ claims.
The storm surge along the Northeast flank of the St Bernard/Lower Ninth Ward protected ring “was not vastly greater than design levels and the carnage that resulted owed much to the inadequacies of the system.” This “critical 11 mile long levee section” was incomplete. Funds had long been requested by the Corps but had not yet been approved by Congress. “As a result, large portions of this critical levee frontage were several feet below final design grade.”
Additionally, the Corps had used “local dredge spoils from the excavation of the adjacent MRGO to construct the major portions of the levees along this frontage. The result was that major portions of these levees were composed of highly erodible sand and lightweight shell sand fill. When the storm surge arrived, massive portions of these levees eroded catastrophically”. “The resulting carnage in St Bernard Parish was devastating, as the storm surge rapidly filled the protected basin to an elevation of +12 feet above sea level; deeply inundating even neighborhoods with ground elevations well above sea level.”
“The catastrophic erosion of these critical levee frontages need not have occurred.” If the levees had been completed in a timely manner, if well compacted clay fill had been used, and if they had been properly armored, then “the result would have been some overtopping, but not the catastrophic erosion and uncontrolled breaching. Some flooding and damage would have been expected, but it need not have been catastrophic”.
The St Bernard/Lower Ninth Ward protective ring was also flooded from two catastrophic breaches along the west side of the Industrial Canal. Limited “overtopping occurred at both of these locations, but this was not the principal cause of either of these failures. Both were principally due to underseepage flows that passed beneath the sheetpile curtains.” “Like many sections of the flood protection system, these sheetpiles were too shallow. The result was two massive breaches that devastated the adjacent Ninth Ward”.
New Orleans East Basin
New Orleans East was protected by its own separate levee ring. The catastrophic failure of that protection was very similar to the failures that led to the destruction of St Bernard and the Lower Ninth Ward.
The storm surge along the Eastern side of the New Orleans East Protective ring “was not vastly greater than design levels and the carnage that resulted owed much to the inadequacies of the system.”
“Levees at the southeast corner of the New Orleans East protected basin… had been constructed primarily using materials dredged from the excavation of the adjacent (GIWW) canal channel, and … contained major volumes of highly erodible sands and lightweight shell sands. These levees massively eroded and produced the principal source of flooding that eventually inundated the New Orleans East protected area.” The catastrophic erosion of this “critical levees frontage need not have occurred.”
The storm surge also overtopped levees along the east side of the IHNC ( Industrial Canal) channel. “This produced an additional breach … along the southern edge of New Orleans East, adding additional uncontrolled inflow to this protected basis. This failure could have been prevented at little incremental cost if erosion protection had been emplaced along the back side of the concrete floodwall”.
Central New Orleans Basin
Central New Orleans is the area west of the Industrial Canal that extends to the Jefferson Parish line. The area is protected by levees and has three major drainage canals that are protected by floodwalls.
There were three (3) catastrophic breaks in the canal floodwalls: “two on the London Ave Canal and one on the 17 th Street Canal. All three of these breaches eroded and scoured rapidly at well below sea level, and these three breaches were the source of approximately 80% of the floodwaters that then flowed into the main protected basin over the next three days”.
“The three breaches on the 17 th St and London Ave canals were catastrophic. None of these failures were the result of overtopping; surge levels in all three canals were well below the design levels and well below the tops of the floodwalls.”
“A large number of engineering errors and poor judgments contributed to these three catastrophic design failures. 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”.
Additionally water entered through breaches on the west side of the IHNC ( Industrial Canal). These breaches “did not scour and erode a path below seal level, so they admitted floodwaters for [only] a limited number of hours”. Only 10% to 20% of the floodwaters that eventually inundated the New Orleans protective basin entered through these features. These failures and breaches … appear to have been preventable. “The installation of erosional protection (eg concrete splash pads or similar) might have prevented the failure.”
