Although most of the levee breaches in coastal Louisiana were the result of the storm's surge flowing over levees, preliminary evidence suggests that three major breaches in downtown New Orleans occurred prior to the floodwalls being overtopped; that is, the floodwalls failed before their design was exceeded. The findings are likely to shape not only the future design of the hurricane protection system but also plans for rebuilding sections of the city and perspectives on the federal role and responsibility in the city's rebuilding efforts. One of the causes of failure being discussed is a poor or inadequate design for protecting the city from a Category 3 hurricane. The original project design was to control storm surge flowing into water bodies near downtown by building inlet barriers and canal floodgates. During the project's construction which began with authorization in 1965 and was ongoing when Hurricane Katrina made landfall, numerous factors contributed to changing the design of how to protect the city (e.g., including local environmental concerns, changing cost estimates, local flood protection preferences, and litigation); the final design attempted to reduce hurricane-related flooding in the city by increasing the height of levees and floodwalls, in lieu of the barriers and floodgates. The Corps' decision in the mid-1980s to recommend higher levees instead of the inlet barriers it had recommended in 1965 was shaped by multiple factors, including environmental litigation, project economics, and local preferences. The decision to not build floodgates, and instead build floodwalls along the canals, was made by the local project sponsors. The original design and the final design were intended to provide the same level of protection, i.e., protection from the rough equivalent of a Category 3 storm surge. This report discusses the evolution in the project's design, with specific reference to how and by whom design decisions were made. The focus is on two major design developments relevant to the current investigations into the floodwall failures in downtown New Orleans' during Hurricane Katrina: (1) the shift from the barriers at the inlets to Lake Pontchartrain to higher levees along the lake; and (2) the shift from floodgates at the mouth of the city's stormwater outfall canals that drain into Lake Pontchartrain to higher floodwalls along the length of the canals. Lake Pontchartrain Project

Congress authorized the Corps to protect New Orleans from the rough equivalent of a Category 3 storm when it authorized the Lake Pontchartrain and Vicinity Hurricane Protection Project in October1965. The Corps preferred floodgates to floodwalls along the Orleans Avenue and London Avenue canals.
Breached floodwalls in downtown New Orleans during Hurricane Katrina caused significant flooding. Unlike most of the flooding in coastal Louisiana which resulted from water flowing over levees and floodwalls as the storm's surge exceeded the structures' height, preliminary evidence suggests that three downtown New Orleans breaches occurred before their design was exceeded. That is, these downtown breaches resulted not from structures weakened by overtopping, but from the failure of the floodwalls and their foundations. Findings of ongoing investigations into the causes of the floodwall failures have implications for analyzing both the reliability of the existing system of levees and floodwalls and its repairs, and options for greater structural protection of New Orleans. Moreover, these findings may shape plans for rebuilding sections of the city and perspectives on the federal role and responsibility in the city's rebuilding efforts.
One possible cause of the failure is a poor or inadequate design. Following Hurricane Betsy in 1965, Congress authorized the Corps to construct with local levee districts the Lake Pontchartrain and Vicinity Hurricane Protection Project to protect the city from the rough equivalent of a Category 3 storm. The project's original design was to control storm surge flowing into water bodies near downtown by building inlet barriers and canal floodgates. During the project's construction which was ongoing when Hurricane Katrina made landfall, numerous factors (e.g., including local environmental concerns, changing cost estimates, local flood protection preferences, and litigation) contributed to changing how the city was to be protected; the final design attempted to reduce hurricane-related flooding in the city by increasing the height of levees and floodwalls, in lieu of the inlet barriers and canal floodgates.
This report documents the evolution in the design of the Lake Pontchartrain project, with specific reference to how and by whom design decisions were made. The focus is on two major design developments relevant to the current investigations into floodwall failures in downtown New Orleans: (1) the shift from barriers at Lake Pontchartrain's inlets to higher levees along the lakeshore; and (2) the shift from floodgates at the mouth of the city's stormwater outfall canals that drain into Lake Pontchartrain to higher floodwalls along the length of the canals.
The Corps' decision in the mid-1980s to recommend higher levees instead of the inlet barriers it had recommended in 1965 was shaped by multiple factors, including environmental litigation, project economics, and local preferences. The Corps preferred floodgates to floodwalls along the Orleans Avenue and London Avenue canals. The decision to not build floodgates, and instead build floodwalls along the canals, was made by local project sponsors. The original design and the final design were intended to provide the same level of protection, i.e., protection from the rough equivalent of a Category 3 storm surge. This report will be updated as events warrant.