Folks are mixing up barges, levee breaches, and witnesses.
The grain barge shown in the images in this thread punched a hole in the east side of the Industrial Canal and flooded the lower 9th Ward, not downtown.
However, the surge of water that pushed the barge into that levee also topped (not breached) the western side of the Industrial canal and put maybe 5 to 6 feet of water in to a limited (call it 20 blocks by 20 blocks) area just northeast of downtown, in New Orleans proper. This either came from the Intercoastal Waterway or Lake Pontchartrain or both, probably both, also probably more so from the Industrial Waterway.
The levee breaches that flooded downtown New Orleans were near the north end of two canals, one east of the City Park (London Canal breach) and one west of the City Park (17th Street Canal).
The pictures from London Canal indicate that the concrete wall was undermined and didn't really fail so much as its foundation was scoured loose. (If you look at it, you'll probably see a "failed" wall, but an engineer or construction guy will see a scoured foundation as the root cause...most likely.)
Several sections of the 17th street canal breach failed as a unit and appear to have been pushed over from the top. There are no visible barges anywhere near there, and it would be very difficult to get a barge anywhere near there because there is a very low bridge between the breach and Lake Pontchartrain. Also that canal is very narrow for any barges to get into it and have much lateral velocity, if they can get in at all.
Odds are this failure came from one of three causes. Much earlier, around 3 AM, the Kenner police reported that the canal NNW of there was full up and that they had some minor water problems. (Probably water coming up out of storm drains.) Since the winds pushing water west and southwest and then south would have caused similar buildup at the canal easts of that one (including the 17th st canal and the London Canal in succession), and since they both have the same height walls, it is likely that the 17th Street Canal was full too.
It is possible that some water came over the top and undermined the foundation from the inside. I rate this as being unlikely because the remaining sections of the wall do not show evidence of having been topped. No green stuff on top of the wall, no piles of the same kind of debris inside the wall as inside the canal.
That leaves two possibilities. One, the hydrostatic pressure of the deepening water in the canal, and the hydrodynamic pressure of the southward moving crest of water, may have forced water under the wall (percolation and then scouring) and caused it to fail like the London breach, but if so, the end result was very different than the London breach because the whole section of the 17th street canal wall toppled completely flat in the hole. Underwater and invisible flat. At the London breach however, the wall sections were still in place and standing vertically with holes under them and gaps between sections.
Therefore, I believe that the ties between sections of the 17th canal wall were not as sturdy as those used elsewhere, that they failed, and at that point, with nothing pinning the top of the wall in place, the water simply pushed it over.
I find it more than curious that the 17th street failure and the London Canal failure both involved new sections of wall, that other than barge damage, no old walls failed anywhere (be careful to distiguish between a wall and a levee), and that both the 17th street and the London breach were possibly both a result of under wall percolation, scouring and subsequent failure.
However, it is very risky to point fingers on that basis because of the different failure modes (at least in final appearance) but slightly less risky is noting that both were new construction.
Before you run too far with this, if you are looking for culprits, give it a day or so. I have this feeling that some.....revelations....are inbound.
While I'm here, two other points, regarding the Industrial Canal Breach caused by the barge.
One, the barge is south of the hole, and the most likely surge came from the north, whether the Lake, the Intercoastal Waterway or both.
Two, the debris piles, in the second image in this thread, are lodged at chokepoints oriented radially away from the breach caused by the barge. That tells me that the great majority of the water in this area initially came from the breach that the barge caused. However, the picture clearly shows that the water is in fact flowing in the opposite direction, out of the breach and back into the hole.
Since water doesn't flow uphill, this may seem like a contradiction, but there is an explanation and I expect it to arrive with the revelations noted in my previous post. Probably late Monday or early Tuesday.
Before you run too far with this, if you are looking for culprits, give it a day or so. I have this feeling that some.....revelations....are inbound.
But you're such a tease too. :)
"Probably water coming up out of storm drains.) "
Water from storm drains in the city could not possibly fill these canals. Only a pump can raise water to a higher level. Water simply cannot flow from a lower to a higher and back to a lower topo region.
You are quite right, it takes a lot of time and energy to research and prove/disprove the many theories.