I've been puzzled by the focus on whether the waters "overtopped" the Levy's. I don't know much engineering, but I lived in Sacramento for many years, of which a large part is protected by a levy system.

In times of serious flooding, the Levy's that were considered a problem by city government agencies were not so much the ones that might overflow, but rather those that shows signs of breech. Engineers from the city were always looking for "wells" alongside the levy rather than at the levy and the height of the water itself. These "wells" look like artesian springs, and can show up many yards from the actual levy itself. They look like pressurized water bubbling up through a hole in the ground.

With the storms, its not just the amount of water that is the problem, it's the extra weight it brings, along with the speed. The extra weight increases the pressure on the water at the bottom of the river to find new outlets. This with the speed makes the river (or canal) become undercut and grow deeper as well as faster. So what happens is that the water can actually force its way underneath the levy to bubble up on the other side. If left unchecked the well can widen and basically destroy the levy from the bottom up rather than the top down. They city engineers always seemed to be more worried about that happening rather than the water overflowing the top. After all, even if water overflows the levy, so long as it remains intact you are probably going to be in decent shape.

Whether this scenario can happen depends more on how deep the levy is, not how much higher it is than the level of the river water. And on what the composition and weight is of the foundation material that the levy is based on.

This is great!
Both positions have merit and it is worthwhile to understand what happened here for a number of reasons.

The main problem is "below sea level".

Dump stones and dredge into the city until it is 20 feet above sea level. We are in the position if opposing irresistable force here. If the city continues to subside it will be at the bottom of a 50 foot well.

Or the city can be moved.

25 years after it is done no one will remember and it will be politically irrelevant anyway

Same data, different interpretation: On the Levees of New Orleans (Update 11)

There is yet another set of factors, that none of these reports have addressed yet. Maintenance and nearby construction. A good friend of mine who aside from being an infantry platoon sergeant is a civil engineer. His firm does flood control projects almost exclusively for the Army Corps of Engineers. He pointed out that the money spent on levee maintenance in New Orleans has been below Corps recommendations for some time. And on top of that, the city has long allowed construction along the levees much closer than Corps engineers, or most competent engineers advise. Lack of maintenance and nearby construction certainly weakened the levees.

Somewhere in the first few days after Katrina, I thought I read that the breach was caused by a loose barge. I never saw anything about it again, and can't help to wonder if I actually _did_ see it - or heard it, perhaps, and if so, if it was known or theorized. Are there barges in Lake Ponchetraine? or just in the Mississippi?

I also saw the story about the barge. It seems quite likely.

Re: Lake Ponchetraine & debris. Why do we need the "big lake"? Drain it into the gulf and use the hole as a landfill in which to put all the destroyed houses, school busses,cars, etc. What else can you do with thousands of refrigerators? No more levy problems, no cars sold to unsuspecting buyers, many problems solved.

I have posted correspondence between Dr. Kemp of LSU and myself on the levee break issue. Dr. Kemp reports no evidence of scouring that would indicate the levees were overtopped. It is now up to the Corps of Engineers to prove otherwise:

On the Levees of New Orleans, Update 12

Latest update, w/news & analysis by guest G.B.:

On the Levees of New Orleans, Update 17