The Levees Didn't Break, It Was the Canals

Everyone said it was the levees initially, but now it looks as though it was the canal system that is part of the levee flood control system.

Here is the official story then:

Some parts of the city were flooded by the initial hurricane. But the major sources of water now appear to have come from breaches in canal walls. One was the 17th Street Canal, which is used for drainage and runs through New Orleans to Lake Pontchartrain on the city's northern edge. A second breach was in a wall in the London Avenue Canal. There are also breaches in the wall of the Industrial Canal (also called the Inner Harbor Navigational Canal), on the east side of town.

What is the difference between a floodwall and a levee anyway?

The canals walls that broke are technically called floodwalls. They are made of concrete and steel, 6 to 10 feet tall, about a foot wide at the top and 2 feet wide at the bottom. They stand on top of an earthen base.

A levee is a broad mound, 50 feet or more wide at the base that rises slowly to a broad crest at the top. You could easily walk or drive up the side of one. These are far more stable than floodwalls. Water can spill over the top and erode some of the levee, but it will still function. When a floodwall fails, it fails catastrophically.

So, relatively small walls broke and caused all the flooding.

A few thoughts:

1) It is hard to believe that the storm caused enough water to go over such that the foundations actually washed away. Granted it was a big storm, but canals shouldn't get such violent wave action as a levee. Also I would think the foundations would be exposed to water a lot just normally.

2) Two foot thick concrete walls would be much easier to blow (with explosives) than a real levee.

3) Can't water flow into a canal be restricted rather easily? Why wasn't the mouth of the canal sealed off?



Here are satellite photos of one canal breech "before" and "after".