Forget the Superdome and a few thousand people who were uncomfortable for a few days. The real story of Katrina has yet to be told. How did a “State of the Art” floodwall become a 200 billion dollar engineering failure?
As engineers analyze why some New Orleans canal floodwalls broke during Hurricane Katrina, a central focus will be Louisiana’s notoriously soft, wet Mississippi Delta soil.
The floodwalls are hard structures embedded in soft material. As Katrina’s storm surge filled up the 17th Street and London Avenue canals, it put high pressure on the walls and soil. If the surrounding soil is already unstable or the structure is not properly lodged in it – it can move and bring the wall down.
Simply put, that’s not good enough. You don’t have a 200 billion dollar failure and say “We’ll it was really tough.” It is not tough. The earthen levees -most of them 30 years old- held and the new “start of the art” floodwalls failed. Saying, “Well, you know, the ground is squishy around here” doesn’t cut it. Engineers solve problems like this. – Well good engineers do.
The Corps and outside engineers say it’s too early to tell what went wrong, and that walls probably failed for different reasons in different places. In eastern areas of the city, where the Industrial Canal is located, floodwalls were clearly overwhelmed by high water beyond their design specs. Engineers are focusing much of their attention on the 17th Street and London Avenue drainage canals, where storm surge was lower and may not have overflowed the walls – pointing to a possible flaw in design, construction or maintenance.
I’ve been hesitant to post any firsthand knowledge or evidence because frankly it is beyond my scope of expertise and I spent less than a day studying it… But I examined the breach in the floodwall at the 17th street canal and frankly I would be hard pressed to argue that the water came within 4 feet of the top of the wall. Statements from engineers who have done more complete examinations support my limited observations.
Given the above let me say this. If the floodwalls gave way when the water was still only about halfway up the side of the wall, it may go down in history as the worst engineering flaw in the history of mankind. Many people -especially the ones who live 1000 miles away and aren’t engineers- have said the the levees were bound to fail because they were not rated for a direct hit from a category 5 storm.
The problem with that, of course, is that Katrina was a category 3 storm and it hit Mississippi. New Orleans got a glancing blow from the weak side of a category 3 storm. Certainly any structure that was designed to withstand a direct hit from a cat 3 storm should have held.
The levee break on the Industrial Canal is somewhat more understandable. They say the water was far higher than the levee. Taking that at face value, the coastal erosion in the area south of the levee has been dramatic for the last few decades. The levee is considerably closer to the Gulf of Mexico than when it was designed. If the storm surge was higher than it was designed for, that is not necessarily indication of a design flaw but perhaps and indication of the changing parameters of the area.
The other two areas, (17th street and London Ave) which are getting considerably more scrutiny, are on Lake Pontchartrain. These have floodwalls which are made of sheet pilings driven into the ground and concrete poured over them..
I didn’t take this picture to show the width of the wall
but as you can see from the guy leaning over it,
the wall is probably about 24 inches thick.
(Click for a larger view.)
…Designers can lessen the upward pressure by putting the structure deeper into the earth; that way the water has farther to travel and the pressure is lessened. But some observations by LSU scientists indicate the sheet piling might have been unusually short – just a few feet long.
Driving sheet piling “has several functions,” Bea said. “The first is to prevent water intrusion below the base of the wall below the ground level. The other important function is to support the wall both laterally and vertically. We have all kinds of photographic evidence that says those walls did not get the support they needed, and over they went.”
A few quotes from a single academic is not exactly incontrovertible evidence but the above statements are nonetheless quite troubling. Although, I’m not sure they can be altogether accurate. I’ll try to get some pictures to make it more clear, but I’ve watched them put in sheet pilings. The pilings have holes on the top end to loop a chain thru to raise it up. If they only put it a few feet in the ground, the construction crew would then have to cut the top off with a torch. That would be a slow process that would make it abundantly clear the piling was not in deep enough. The LSU guys claim to have photographic evidence but I’m still taking this one with a grain of salt.
The whole story will unfold in the years and decades to come in the court system… but in the mean time, I can’t wait for the Discovery Channel version. Early indications are that this was more than just an act of God… It looks like the flawed hand of man had more than a little to do with it.
Update: A few folks in the comments have (rightfully) made the point to separate the engineering from the construction. That is a big point I should have made. I called it an “engineering” failure because in the generic sense it was a failure of an engineering project… But if we are looking for the true flaw, construction is, of course, half of the equation.