One thing I don't understand is why the canal is there in the first place. Apparently the neighborhoods where flooding began are a sufficient distance from Lake Pontchartrain. But then this safety margin is erased by having a canal go from the lake to a point where only a narrow levee protects the whole city.
Well, the Industrial Canal is there for navigational purposes. But the other canals seem to be for flood control. Water is pumped from the bottomland over the wall and it drains into the lake. Why this water could not be pumped through large concrete pipelines, I don't know.
Canals in low-lands are necessary for port operations and drainage. Ever been to Florida?