I've had a couple of posts in the hopper while waiting on some last few pieces of information. I'm going to break into that info early, because I think it's important...
Two major levees-related news items today:
Analysis finds flaws in pumps at outfall canals. (Refers to M.W.I. Pumps)
Corps revises London Ave. Outfall Canal ICS operating procedures. The big news is that the safe water level has now been reduced so low (about 2.5 feet) that the pumps will now run during all major rainfall events.
What does this mean in the big picture?
The current setup was a temporary fix based off what the Corps could assemble as quickly as possible after the storm. (From Page 10 of Parson's Report)
The interim setup, even if every single pump operates flawlessly to its full design capacity, is only designed for a 10-year (UPDATE- "rain") event. We've heard many times how much of a joke the 100-year level is. The 10-year level is even weanier.
Pumping Station #6, which feeds the 17th Street Canal and is the main pumping station for the city of New Orleans, is capable of putting out a little over 10,000 cfs. That's an admitted shortfall of over 20% at that pumping station. In a big enough storm, water will begin to back up. In a short/lightish storm, the only thing that will probably happen is street flooding and maybe a few flooded cars. In a long-lasting/high-intensity storm, large parts of the city , especially Gentilly (drained by PS#3 & #4), Mid-City and Lakeview, will flood.
The parts of the floodwalls that failed were repaired quite thoroughly. The Corps rebuilt those parts with T-walls with ample foundations. But, the parts that didn't fail were left untouched. There's been a about what the safe water level for the Canals is. Each time the Corps has investigated, the walls have been derated. The walls SHOULD be rated to their top (a little over 10' elevation). Instead, they've been derated, especially on the London Avenue Canal, where they'll now close it at 2.5'**. There are currently no plans whatsoever to rebuild the walls or repair them in any way. The Corps says it would take too long and would take too much money and they'd rather get the permanent pump stations online.
If you were to sit the major engineering experts in the area down and ask them what the 3 most important projects are for New Orleans, I'll bet the lion's share would include the permanent pump stations at the mouths of the outfall canals. When the "10-year storm" standard was adopted (~ early 2006), the Corps was planning on having the permanent pump stations in place no later than 2010. Had they been replaced then, the 10-year storm standard may have been reasonable. Now, they're officially saying it will be complete by 2012, at the earliest. The Corps has picked up the pace, but it's looking more like it will be 2013 at the earliest before the stations are complete. The longer it takes for the permanent pump stations to be built, the more maintenance will be required and the more one should question the original design basis for the pumps.
Bottom line: The pumping capacity of the City of New Orleans is seriously constrained. Sections of the city, especially Gentilly, Lakeview, and Treme/7th Ward, WILL flood in storms significantly less intense than the minimal 100-year level we expect, even without a levee breach. The extent of the flooding will be proportional to the storm intensity and duration. The system will not be fixed for several years at the current rate. Major weakpoints in the system (the weakened walls) will still not be fixed by the time the system is complete.
I hope that sums things up without droning into too much detail.
* I'll leave the "contractual" issues for others to comment on, I'll stick with my expertise. From what I understand, the Corps basically called around to see who could supply the most cubic feet per second (cfs) by next hurricane season. That particular time, because of rising commodity prices, was a bad time to be buying heavy equipment, especially pumps, especially pumps that large. I'll give the Corps the benefit of the doubt and say that, among those they contacted, MWI had the most cfs with the quickest stated delivery.
** Safe water level used to be about 5' with closure at 4'. Now it's 4' with closure at 2.5'. The Corps has said they will take whatever measures necessary to stop the level from rising in that Canal, including shutting off all pumps feeding the canal until their pumps can catch up. It's already happened several times. The canal walls have been derated so much, I'd curious how they justified the decision to give them any rating whatsoever.
PS- Thanks again, Matt McBride. Fix the Pumps is a great reference site.
NOTE: Some minor edits after initial post.
UPDATE- See comments.
UPDATE 2- London Avenue floodgate closes today (9/12) due to heavy rainfall.