The flood disaster of New Orleans due to hurricane Katrina in August 2005 can provide valuable lessons for the design and maintenance of European flood defence systems. The system partially failed because the design conditions (water levels, waves) were exceeded by the hurricane. The other part of the system failed at water levels below design level due to geotechnical failure of the floodwalls’ foundations. The disaster showed the importance of a careful determination of design conditions, the significance of transitions and objects on the slopes and it showed that geotechnical failure is of major importance for the reliability of flood defence systems.