Overall, I think that levees are effective in being able to hold back water from communities and other areas. There has to be a continual examination and reexamination of levees because erosion due to constant water pressure can cause them to give way and cause massive calamity. Given the fact that levees are the results of engineering and construction with population in mind, for the most part, they are effective. Yet, when they fail, it reminds everyone of the need to never take them for granted. New Orleans' levee technology in the aftermath of Hurricane Katrina is an example of what happens when levees are not properly assessed and reexamined on a continual basis:
The words levee and levee breach were brought heavily into the public consciousness after the levee failures in metro New Orleans on August 29, 2005 when Hurricane Katrina passed east of the city. Levees breached in over 50 different places submerging 80 percent of the city. Most levees failed due to water overtopping them but some failed when water passed underneath the levee foundations causing the levee wall to shift and resulting in catastrophic sudden breaching.
The events in New Orleans have brought to light that while levees are overall effective, like any other solution to natural calamities, they are not perfect and must be subject to assessment and reassessment in order to be considered a means by which to deal with the pressures brought on by water.