Well, there's several questions rolled up in your post.
These sections were rebuilt by the New orleans Sewer and Water District and the Orleans Levee Board. They hired a pair of design firms who originally recommended 35 foot piles, ignored them and let contracts for 17.5 foot piles.
After the work had started they allowed the Corps of Engineers to inspect the design, and the people tasked to this were uncomfortable with the 17.5 foot tip depth, but were overruled by their superiors at the CoE, who wanted to observe the performance of the piles while working up to a project to cap the piles with concrete walls.
The documents I've seen indicate that the Corps mandated the 17.5 foot depth, and there has not been sufficient explanation as to why the piles were only driven to ten feet.
The simple fact that there's a question like this raises concern about other projects undertaken by locals without the Corps of Engieers as lead agency. There is a fourth section of capwall, across from the north London Canal breach, where the capwall was leaned inward about three feet and showed evidence of significant amounts of water flowing in under the sheet piling.
In my opinion, the porobability of additional failure cannot be discounted, and depends mostly on how many projects were designed by the locals, unsupervised in the critical early stages by the Corps of Engineers.
However, I wouldn't base a decision to stay or evacuate on the answers to this question. The levee breaches and failures that already exist are more than enough to prompt me to get out.
The malfeasance of the Levee Board and the Sewer and Water Board are icing on the cake.
Thanks,
My take is that these "coastal wetlands preserve" folks have it bacasswards.
The engineering way to protect NOLA would be to raise it via dredge and fill creating a super Venice (or Punta Gorda). Or defend it the way the Dutch do. Looking at the maps this would first entail a huge dyke along the eastern "shore" of the Lake, drain the Lake (windmills), put in a series of dykes and canals, and turn over the newly reclaimed land to dairy farming. To the south of NOLA there needs to be a series of cencentric dykes with coffers, canals and emergency pass-throughs.
I'm sure this would cost a ton but making a bit more swamp and keeping people off of it is a waste of time and money and as long as that lake is there and full it presents a hazard to the city.