How effective are levees as a method of river management?

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:

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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.