When the water is finally pumped out of New Orleans, a lot of the city is going to remain irretrievably ruined. I’ve been to NO – most people appear to live in one-storey wood-frame houses, and they’re not going to be good for much after a month under the water. The wood will rot. It might be an opportunity for some enterprising developer to buy up a section at rock-bottom prices, bulldoze all surviving structures, truck in a whole lot of rock, gravel and dirt, and build up what amounts to an island with its top above sea level – an island that would remain dry even if the levees broke again. And then build new homes on it and sell them. If this process were repeated often enough, perhaps most of the city could be elevated above the floodplain. Would this be possible? Or cost-effective?
It’s been done a few times. I seem to recall Seattle did that. And my town of Marietta did it a long time ago.
During last years floods part of the downtown region (a parking lot) disappeared into a sinkhole and reveal a layer of street and such 20 feet down. Interesting as all hell.
My understanding is that the subsidence problem really is too great to overcome - that is, unless the mighty Mississippi is once again allowed to flow where she wants to flow, thereby depositing silt all over the massive delta region, well… realistically the greater New Orleans landscape will continue to sink - even if you artificially build land fill on it. Eventually it will still sink…
In short, some places are just foolish to live in. Perhaps the Dutch could offer some opinions however. Realistically they’re the only people on the planet whose engineering opinions I would trust right now.
In Isaac’s Storm, it is related that after the hurricane of 1900 wiped out most of Galveston, enough fill was brought in to (as I recall) raise the level of the city by 10 feet. Surviving buildings were elevated with the aid of something called screw jacks (in what must have been an amazing feat for the time). Of course, a seawall was also built.
I’m sure repeating this on a New Orleans scale would be very expensive, but impossible?
It’s possible- my home town (Sacramento) did it in the 1860’s, after having a major problem with flooding during its’ first decade of existence.
It’ll cost a lot of money, but it can be done.
Screw jack: Imagine a big screw, with a flat bit on top, in a support. You unscrew the screw, the top goes up. Slowly. Huge mechanical advantage. My grandfather had a few of them, they used them to lift locomotives with. And houses.
Are you suggesting NO homes should be fitted with screw jacks to be used in case of flooding? Or that screw jacks could be used to life them so permanent fill could be inserted underneath?
Well, you could use them to lift the houses so fill could be inserted underneath… if the houses were sturdy enough. In the specific case I’m thinking of, a gully-washer washed out the ground under a corner of a house, so my grandfather took a screw jack and, you know, held the house up with it.
But I wouldn’t, if I could avoid it, make it permanent. I’m just saying what they are. And why they work for lifting heavy things. Pure mechanical advantage, like a screw.
It’s not much of an engineering feat, or anything. You ever see a boat out of the water on jackstands? Jackstands are a variant on screw jacks, usually.
It’d be a lot of time and effort to do it to every house. You’d need like six or eight on each house, and you’d pretty much have to turn them in synch.
In Sacramento, the preferred method was to fill in the first story and convert everyone’s first story in to the ground floor. The streets were lifted and filled, but the sidewalks were left as corridors (now closed, sadly, and mostly taken over by the homeless) so that shoppers could stay out of the sun. You can still see the original street level in some allyways.
This (along with moving the river a bit, the Folsom dam and a levee system) stopped the yearly floods that kept wiping Sacramento off the map. But it isn’t really going to help Sacramento in case of a major flood. Sacramento is the most likely to city in America to see a major flood, and it’s already seen some pretty bad ones. And they keep building new subdivisions on flood plains. Those big doors on Folsom Blvd. near 65th street are intended to keep the flood in or out of downtown Sacramento.
Anyway, I’m sure if it could be done, it would be. One things I can think of is that New Orleans has a very high water table (to the point that the preffered way to bury corpses is above ground) and nobody wants sludgy saturated fill. I also think there is a bit of an earthquake threat in NO, and fill and earthquakes go together like fire and dry forests.
Yep. Unless there is some overwhelming reason that the city **must **be in that specific location, you’re fighting a losing battle. The levees are a mixed blessing-- yes, they keep out the water, but they are the reason that the city is sinking in the frist place since silt is no longer deposited.
I’m sure we could engineer a solution around this if money is no object, but money is always an object.
Politically, of course, the decision has already been made. We’ll rebuild in the same spot, try to keep back the waters again, and sooner or later we’ll fail.
I saw a demonstration of this effect once on television…pretty remarkable. When water saturated landfill got shaken the land fill sort of “liquified”. It did not turn into a liquid of course but things sitting on top of it just sunk as if the solid ground beneath them was no longer solid and more like a liquid. The demonstration was done after the San Francisco earthquake where you saw some four story buildings that sunk straight down so the fourth floor was at groundlevel. People on the first floor had to walk up to the top to exit the building.
It was a weird and startling demonstration but it does not put a lot of faith in structures built on landfill in me. IIRC that new airport in Japan where they built a whole island offshore for it is sinking. No matter what they did (e.g. dropping huge weights and such to compact the ground) it still slowly sank. The solution is the screw jacks mentioned earlier. The entire airport structure is slowly and perpetually jacked up (they use laser levelling and computers to manage it all).
How could that be applied to NO?