Rebuild New Orleans but 'Floodproof" it first by filling.

Here's one approach to "flood-proofing" New Orleans: 

Raise New Orleans above sea level by filling.

Fill the low-lying parts of New Orleans with "structural" fill...i.e. something you can build on. Not cheap but nothing is cheap when building by the water. But it seems pointless and even unethical to encourage people to move back into a city which could flood until the time we have flood-proofed it.

Suppose we figured we were inspired by the walkability of New Orleans (or at least so I am told) and wanted to re-create a fairly compact city. We don't have to fill approximately 20% of it i.e. the area which includes the French Quarter and which was not flooded. This area makes up about 20% of Old New Orleans, I have read. So let's just say we want a flood-proof New Orleans of about 3 miles by 3 miles -- you can walk across it in an hour. Now that's not a big city by any North American standard but as a pedestrian-oriented city of 9 square miles -- three miles in either direction -- it is not too shabby.

So two, immediate questions are

1. What would it cost to bring New Orleans up-to and above sea-level grade with a suitable structural fill?

2. Would/could such a fill be stable?

I'll dispense with the second question -- I simply have no remote idea -- and leave that to the geologists and engineers to tell us if such a massive fill could be stable for the next few centuries.

I have no idea what sand/gravel/aggregate costs in southern Louisiana. I suspect that the nearest source would be hundreds and hundreds of miles away. But let's guess (based on wild extrapolation from Seattle costs for a 10 yard truckload) that structural fill could be placed/compacted etc in New Orleans (I assume it is delivered from upriver by barge) for $15/cubic yard. Assume an area to be filled of 3 miles by 3 miles (9 square miles total.) Assume a fill of 25 feet on average. Multiply it out and you get a number just shy of $4 billion. Not too bad, all things considered? And just to make sure no one misunderstands, I am talking of filling only those parts of New Orleans which are below sea level and which were destroyed by Katrina, which I understand would exclude the French Quarter etc.

Food for discussion, at any rate.

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Btw, my calculation is that at a low-rise density of 40 units per acres -- quite common and by no means "high" density -- upwards of 200 thousand people could live in this nine square miles.

•••

Thanks, Laurence, for pointing out How do they rebuild a city? I will be curious to read the (I hope inevitable) analyses. I wonder if in fact, with a commitment to finish the job from the Corps of Engineers, you couldn't create some liquidity for New Orleans property owners whose property is now practically worthless.

Comments

[Hamsterbaffle]

Interesting idea.

That would mean abandoning not only the houses and single-story wooden buildings that lie below sea level, but a significant number of large civic buildings as well as huge amounts of infrastructure (pipes, gutters, streets, etc). Not everything will prove to have been totaled by the flood. Wouldn't we need to calculate the loss of all of that already built and perfectly salvageable stuff?

[David Sucher]

It's my impression -- and please do bear in mind that I have never even been to New Orleans much less know the current situation -- that the frame houses which are below sea level are destroyed and not salvageable. As to condition of the roads, sidewalks, sewers, water line and the civic buildings, I have no idea either, of course. We shall have to wait and see what is still useful before we could do a thorough cost-benefit analysis. But please do bear in mind that the best and most sustainable defense against floods is elevation. Everything else requires mechanical interventions which depend on vast & continual inputs of energy and attention.

[dustin]

You're idea reminds me of what was done in Seattle (on a MUCH smaller scale) to "level" the roads in downtown. And has led to the "underground tours" in Pioneer Square. In many ways, the tourist areas of New Orleans would be well suited to a similar underground world, as it would compliment the "above-ground" cemeteries and the dark religious themes. The problem with this "vision" I've created is that the area that could survive a "fill" without completely loosing its character is the French Quarter, which is one of the few areas that doesn't need a fix.

[Kent]

This can't be remotely possible. Just building the levees alone took decades. What you are talking about is turning the entire city into one giant levee. You'd probably need a train of dump trucks working 24 hours/day for a century to haul that much fill into the city.

What was done in Seattle is different. Seattle washed it's existing hills down into the flats. New Orleans has no existing hills to use. A better comparison would be Seattle's 3rd runway expansion. How many years has the port been filling the land next to the airport just to build a new runway? Multiply that by thousands for an entire city.

We have the technology to build adequate dikes. The Dutch know how to do it. It's a simple engineering exercise and the technology has pretty much been available since the days of the Roman Empire.

I think adequate levees could be designed that would protect New Orleans. Not just levees but a better system of canals with gates and locks so that flooding in one area can be immediately be isolated.

Probably the bigger concern is going to be how to decontaminate the city. It looks like the city will be soaked with a pretty toxic witches brew of chemicals and microbial contamination. How are they going to clean the soils and buildings? I expect every building that has been flooded will need to be stripped of all absorbant material up to the flood line and then be sealed and rebuilt. That means blasting all the brick and concrete buildings down to the brick or concrete and then re-installing new floors and walls. It will also require all new wiring in buildings that have been flooded. Wood-frame structures will be a nightmare to restore and most will probably be bulldozed if they had more than a couple feet of water in them because the walls will be impregnated with toxins. I can't imagine what it's going to take to clean and rebuild that city.

[David Sucher]

Kent,
I agree that elapsed time is an important factor. But modern earth moving equipment is pretty amazing. You've seen pictures of the kind of machines used in big open-pit mines? They can move incredible amounts of material.
Overall my question is a pretty objective one which can be answered by people with accurate knowledge of how much aggregate a barge can carry, how long it takes to unload a barge, how many barges can offload simultaneously in NO etc etc etc...

I don't have that knowledge and until I heard an analysis from someone who does have that expertise, I wouldn't be so sure I'd accept a statement like "This can't be remotely possible." and I would consider my question an open one.

[Laurence Aurbach]

An excerpt from Sunday's Chicago Tribune:

One far-out proposal: Raise the level of entire neighborhoods by "upfilling" with material dredged from the gulf's floor. In the flooded sections of New Orleans that make up 80 percent of the city's acreage, much of the wood-frame housing likely has been destroyed.

"Once you clear away the destroyed housing, you have a chance to raise the grade of the city," said David Schulz, director of the Infrastructure Technology Institute at Northwestern University.

But such a costly, sweeping plan would risk unintended consequences, other experts said. Loading more landfill could simply weigh down the land and push New Orleans lower, a major consideration in a region that has sunk up to 10 feet over the last few centuries.

[Roger]

The comment about the city sinking further is key. I wish I could find the link to the material about the city. But essentially, as the bog the city is built on continues to dry out, it will continue sinking.

Raising it would help in the short-term, but at tremendous cost. And the city will continue sinking.

It's a catch-22. New Orleans cannot survive without it's marshes and the marshes cannot survive with New Orleans.

[clew]

Cheaper than trucks might be choosing how to make the river dump some of its silt in the city, as well as some out in the marshes that need rebuilding. But that might be slow, and New Orleans might need the marshes more, and the point that marsh soil will continually compact seems to override it.

So how are we at building floating cities? Mexico City managed without modern technology (which I remember from Cricket Magazine, so take that with a lot of salt...)

Although the other problem is that floating structures would, I guess, be as much more vulnerable to winds as they are less vulnerable to floods... Could you build piers that can be lengthened as they sink, so that structures slowly climb up their footings?

Me, I would ask the Dutch for their advice.

[Murph]

Boston's Back Bay is on made land. Chicago raised their street level by between 4 and 14 feet in the 1850s-'70s. I assume, therefore, that building on fill is perfectly fine, but that the problem would be what's underneath. The only thing I know about New Orleans' geology (like everybody else, it seems) is that it's sinking / settling slowly. I don't know whether you'd be able to fill your way out of that problem.

[Expat Teacher]

This is an interesting, but with global warming probably increasing sea levels by 1-3 feet (at a minimum) in the next 100 years, shouldn't we build New Orleans to at least those levels? That would add another significant amount to the overall cost...

[Kent]

Out of curiosity I've been reading a lot about the Dutch. Their approach is to live with water rather than try to only keep it out.

Personally I think there are more elegant and sophisticated solutions than simply the brute force of fill.

First of all it would seem that any "Nuevo" New Orleans should be built along the same sort of engineering principles that are used when designing ships. Namely, compartmentalization. It would seem possible to design a much more sophisticated system of dikes and levees with redundancies and fail-safe systems built in so that a single collapse of a canal wall doesn't flood the entire city but only a small section of it. Just like how ships are designed with multiple water-proof compartments. That way the next 1000-year storm might only flood a small part of the city eliminating most of the crisis we see today.

Second, and this is something the Dutch do well, new streets and structures should be designed to take some level of flooding without damage. The Dutch actually design floating houses. That might be unreasonable in a major metro area. But at a minimum, the structures in low lying areas could be designed to accommodate some flooding without major damage. For an example of this, drive through the Skagit Valley north of Seattle and look at some of the older farm houses. They are built on very tall foundations with a lot of steps up to the first floor so that they can take substantial flooding without ill effect as the Skagit used to flood a lot before the current system of dams and dikes was built. New houses and offices built in New Orleans could be designed so that the first floor is "floodable" in that it is just storage space for cars and such and built of materials that can withstand flooding without damage, such as sealed concrete blocks. Living areas would be built above the flood zone and utilities would be designed so that they aren't taken out by flooding.

It would be even easier to design commerical districts this way. Follow the Seattle model of raising the street level to the 2nd floor and using the area below for parking and that sort of thing. Just like the old Seattle underground except rather than abandon the old street level, use it. In fact, I can imagine a fairly unique and sophisticated urban design in which the streets are two-level. Commercial traffic, deliveries, trucks, and that sort of thing use the old lower street level. Pedestrians, cars, and bikes use the new upper street level where the new storefronts are located. If the city floods with 20' of water it doesn't really affect anything except eliminate all the service entries and service access. There is an old city in Mexico that is sort of like this. The city of Guanajuato. The streets are tiny and narrow and mostly for pedestrians. Cars traveling in and through the city travel on underground streets which were originally designed to acommodate flood waters.

In any event, I'm sure there are many hundreds of talented engineers and architects who do this sort of thing for a living.

[David Sucher]

Kent, Interesting comments indeed.

But my tendency, in general, is to favor a low-tech solution, which in this case might be filling.

You write: "It would seem possible to design a much more sophisticated system of dikes and levees with redundancies and fail-safe systems built in so that a single collapse of a canal wall doesn't flood the entire city but only a small section of it."

I agree. It should be possible to design such a system. But can we build and maintain it? I have my doubts.

Now I am not saying that filling is practical but I am certainly initially suspicious of sophisticated solutions to anything.

[Chris Burd]

In a similar vein, Steve Sailer suggests rebuilding NO as Venice:

http://isteve.blogspot.com/2005/09/rebuilding-new-orleans-as-venice.html

Quote:

"You could bulldoze the ruined houses down, then dredge the streets out deeper into water courses with a decent draft for pleasure boats. Take the mud you've dredged up from the streets and heap it up on top of the rubble so the next generation of houses are built above sea level. No streets, just canals and big sidewalks. (I'm sure an engineer would know a better way to do it. but you get the general idea: instead of everything being 5 feet below sea level, make half of it 15 feet below and half of it 5 feet above.)"

This doesn't address the problem of the land sinking further -- a problem in old Venice too.

[David Sucher]

As to the subsidence issue, I wonder if we stopped pumping groudwater out from under New Orleans, as I assume we have been doing for the past many decades, whether inflitration of water back into and under the fill would cause the land to rise?

[Omri]

Before the Aswan dam, the Egyptians had a whole industry that used mesh traps to scoop silt out of the nile for use in brickmaking. Since the whole problem is not enough silt being deposited, why not scoop it from the river and dump it in the bowl?

[sally]

I hope you are all off base. Interesting how people with no knowledge of the city or it's architecture have so many opinions. N.O. can be rebuilt, and I'm betting many of the wooden homes will survive. Most are made of cypress which, for those of you who've never lived in Louiisan grows in the swamps. It's MADE for water.
At issue more is the foundations, built often of a porous brick. I'm hoping that these great houses will be salvaged and restored, even if they must be put up on stilts. Don't write them off, yet. They are far too interesing and beautiful and intrinsic to the culture of New Orleans to be replaced by ticky tacky boxes or (wretch!) high rise apartments!

[David A. Sheppard]

Here's a novel idea: Rebuild New Orleans, with the low parts as AN AMERICAN VENICE. First, divide the areas between the high sections (didn't flood) and the lower sections. Rebuild the lower sections on pilings & compact fill, say, 15 or 20 feet higher. Then deliberately raise the water level higher than Lake Ponchetrain & the Mississippi surge. If it's higher, it wouldn't get polluted by lower-level flood debris. The cajun river culture could thrive, tinged with some of the style of Venice. Eventually the waterways would silt up somehat making them shallower, but that would just balance out the current compaction of the existing land. Prepare the Gondolas!

[Evan]

I don't have any opinion on whether the idea is practical, but I can offer some historical support:

When Galveston was destroyed by a hurricane in 1900, they raised the island by as much as 17 feet with dredged fill material, including jacking up and filling underneath 30,000 buildings that had survived the storm. The process took less than ten years.

[jeff]

The building codes for hurricane-affected areas needs to be changed.

While they look odd, domes seem the way to go… hurricanes and tornados go up to about 400psi on the surface of a structure. Normal, even strongly-built conventional structures go down at far lower than 400psi. Domes can stand over 2,000 psi of direct pressure, and this isn’t factoring in the fact that a dome is also more aerodynamic and will not be affected in the same way as a conventional structure. You can get as much as or even MORE square feet of space in a dome for the same cost/amount of material used as a conventional structure. heating/cooling is apparently much much cheaper for a dome. People have been worrying over how much MORE it’s going to cost to “storm-proof” communities bordering the gulf and atlantic… how about NO additional cost? Just stop building with wood. There’s a dome in florida that’s been through 3 hurricanes with essentially no damage whatsoever:

www.domeofahome.com

www.monolithicdome.com (these seem to be a superior product, comparable price to conventional structures, apparently very little maintenance required)

http://www.aidomes.com/ (CHEAPER than conventional buildings… probably only a litte less sturdy than the monolithic type but still much more resilient than standard wood frame, a little more maintenance required)

…or if you absolutely must have a home that looks conventional (they say they are competitively priced vs. conventional homes)
http://www.concretebuilthomes.com/

if people will only rebuild with one of these, they won’t have to rebuild again… and the taxpayers won’t have to bail them out again. The rule should be, rebuild like this or move inland. We don’t need to spend more money for this to happen. We need to spend the same amount of money on something OTHER THAN wood frame construction.

[Brian]

Here is my take...

It costs too much to raise NOLA because it would destroy existing infrastructure. I'd rather see a more compact city without all the urban sprawl. Kinda like Amsterdam (which is also below sealevel.

I think that New Orleans East and the 9th Ward should be abandoned. A levee should be built to compartamentalize those sections of the land from the rest of the city. Maintain the levees in those areas as dry ground! Pay the folk that live there a handsome sum for their property.... And when the next hurricane comes, use that land as a flood plain! Open up gates and ALLOW the lake to flood into those locations in order to keep the storm surge from swamping the saved parts of the city.

Those areas are already so contaminated anyway...

[Joseph Russell]

Rather than subject anyone to living below sea level, I would sugest filling in the low levels of New Orleans. This should be viewed as a long term project even if it takes ten, fifteen years or more. It can be done in stages with reoccupation occuring as the work progresses.

Where would the land fill come from? Think of projects such as building a trans America or trans Canada railroad and the volumes of earth that had to be moved to achieve such projects. Think of the construction of the Panama canal, the Chunnel between England and France, the volumes of earth that are escavated for sub terranean levels each time a highrise is constructed.
Also think of this: Garbage disposal is a huge problem for cities throughout North America and probably the rest of the world. Landfill could be moved by truck, rail and sea. I once worked out of an office where curiously there was no basement or ground floor. There were also pipes sticking out of the ground in the back. My inquiries resulted in the explaination that the building was constructed on a garbage dump and the pipes were there to vent methane gas. About twenty years later the original building was demolished and the new building had a ground floor. Methane gas was apparently no longer a problem. Cities with garbage disposal problems all over the world might be glad to pay to transport their garbage to the flooded areas and some of those huge three-story tall machines used in mining can be used to compact the garbage.

There is no need to rush for an overnight solution. Rebuilding can be done in stages and the original city layout---streets, historic buildings etc could be replaced as before but at a higher and safer level. This, I would think would be preferable to living below sea level surrounded by a dyke thats not garanteed to protect you. The Danes and pre-Katrinna New Olreans had no choice but this is a golden opportunity-- do it right, you do it once.

In closing, I am not an engineer or a geologist, but many projects involving moving volumes of earth in tunnelling through mountains and building canals were done using engineering techniques a hundred years old. Why not now?

[Craig Hoaglund]

Filling in the below sea level areas of New Orleans is probably the best long term solution. This could be done with conventional fill methods as well as newer methods like those used in the Middle East. The tiny nation of Dubai is making hundreds of man-made islands by dredging sand from the ocean bottom. An elevation of at least 10'+ above sea level would be needed. Underground infrastructure would need to be replaced or modified, but this happens on a regular basis in most American cities anyways.

Examples include the new man made islands in Dubai, Kansai airport in Japan, Battery Park City, NY. (landfill from original World Trade Center excavation), etc.

Once the area is filled in, the money spent on maintaining the now, not needed levees, could be used to pump fresh water into the sedimentary soils beneath the city. This would slow or eliminate further subsidence. Large buildings could be designed so as to allow hydraulic jacking and shimming when required. Slab on grade buildings could be simply mudjacked with hydraulic concrete from time to time. (This is done every other year here in Wisconsin where some buildings have been built on old marshes)

Either way this is a classic example of "Pay now or pay later", or "You get what you paid for". Not including reconstruction, just think of the money that would have been saved by avoiding all the rescue and clean-up operations. Higher property values and reduced flood insurance costs would also result from an above sea level New Orleans. Not to mention the saving of lives in the long run.

Craig Hoaglund
Waukesha, WI

[Steve Holland]

The article on the Galveston raising is fascinating (http://www.americanheritage.com/articles/web/20050908-galveston-hurricane-gulf-mexico-1900-engineering.shtml>Raising Galveston). If you contribute to this discussion you should read this first. The whole process was done with hydraulic movement of sediment. In Galveston they didn't have the benefit of wide areas destroyed and easy to fill. New Orleans would actually be cheaper to fill then Galveston was (inflation adjusted, of course).

[Manhattan Mold Removal]

$4 billion is nothing compared to the costs of clean up after the flood. It's well worth it.