The difference between a "levee" and dikes (not the minority group), flood control walls, canal walls and storm surge walls? A levee is made by piling dirt to varying heights and ten to twenty feet wide at the base or more; the top is more or less rounded. Levees did not break during Katrina; the levees overflowed. Flood walls etc. are concrete or even steel walls built to whatever specs are desired and are nice and tall, not very wide at the bottom and can break under repeated stress at various places. It was these "walls" that breeched and one was rendered useless by a runaway barge weighing several thousand tons that crashed into it. Levees are an ancient method of controlling floods, long before steel and concrete were available. The old Ancient Egyptian song (2000 B.C.), "Waitin' for the Pharo Ptolemy" mentions levees many times.

..go down on the levee,
I said to the levee,
and we'll join that shufflin' throng.
Hear that music and song.
It's simply great, mate,
waitin' on the levee,
waitin' for our pharo Ptolemy

Egyptian levees on the Nile are still in use today. So what is a dike? They differ in that they are used to restrain sea water from invading established land mass. Historically, a dike is used to divert or restrain flood waters from tidal bodies of water such as the system of dikes which protect the Netherlands. Earth levees can break if subsoil erosion is not corrected. Here is a NYT piece from LSU profs written in 1992 that expanded on the much published Times Picayune piece written in 1977. Many of the "possible" solutions they proposed included insane costs as they acknowleged in the piece. In response to some nasty emails questioning my intelligence regarding industry in New Orleans I suggest you go to the interactive map at the above link. You will find that New Orleans city is like an old world castle isolated by levees from everything else. The oil rigs, refineries, gas fields and port are not a part of the city, but lie much further south and yes there are a lot of good jobs in those areas but there is no indication that the workers live in New Orleans or that any of the towns on the route to the port pay any taxes to the City of New Orleans. Late add: Maxed out has a pretty good overall view of levees vs flood walls: bottom line with her as well is that the levees held and the walls did not.