Posted on 09/04/2005 7:20:44 PM PDT by jonatron
Actually, it is easier than that. All they need to do is create a backing behind the levee, plant steel rebars and pour concrete in the water between the backing and the levee. This is usally done with slurry (I think that is spelled) but it should work. The concrete will go to the bottom and eventually displace the water to the point where there is nothing but concrete. Then let the concrete dry. And you have a concrete steel re-enforced levee behind the original levee which should now beable hold the water back, as water is pumped out of the city.
Unless with water seeps up through the ground, which could happen in New Orleans. In which case, you have a whole new set of problems to work out.
They said they want to remove the water slowly to avoid what you described. I'm sure the locals would like to see the water pulled out as fast as possible.
"all it takes is a terrorist with a modest amount of explosives in a barge or boat to breach a levee and submerge the city, say at 3am while everyone is sleeping. "
Youch!
Does anyone know why these long skinny canals with hundreds of miles of vulnerability don't have locks on the end where they go into Lake P? - So that they can be shut to limit the damage?
You seem to know about the canals.
Do they have locks on the end to limit flooding in case of a break? And why such a big profile if just for drainage?
I would think that something on the order of 6' dia. would be sufficient given the size of the pumps.
"200 linear feet of breech does not/will not compare to a 'hole' attempted to be blown by some terrorist when the lake level is nominal (low IOW) ... "
I am sure the initial breech was not 200' - typically, scouring from a small breech will widen levees many time over.
I asked exactly the same question on an earlier thread today. Tonight on Anderson Cooper, a significant amount of time was devoted to this very subject (you might want to read the transcripts when they come out). It's not just sewage and dead bodies but oil and household waste and so on. Cooper was out in a boat with a researcher collecting samples amongst other things. The answer is that everything that gets pumped out of the city will end up in the gulf - and the plan is to do exactly that (and in fact, as you know if you have been watching TV, the pumping has already started). Cooper mostly asked the right questions of the various environmental pollution people he had on but the decision appears to be made. Essentially, there is no time to analyze the situation but gut feel tells the guys in charge that the environmental (and other) hazards of not pumping it out as quickly as possible is worse than the hazard of allowing all this untreated diseased and toxic water be allowed to go straight into the gulf. The EPA has already given them clearance to pump away. At the end of the segment, Cooper introduced a fellow as an 'environmental expert' who said (in between all the snipes and Bush bashing) that it was absolutely the wrong thing to do to pump it into Lake P. (gulf) and it would be a total disaster and horrible mistake if they did. Unfortunately, time was conveniently almost up - I was hoping that Cooper would have been able to ask 'so what do you think should be done with the water'. I have since fired off an email to Cooper ask him why he would leave such an important question dangling like that. I'm not holding my breath for a response. In thinking about it, I really don't think there is a realistic alternative. A treatment plant that could handle the kind of capacity required here doesn't exist - let alone the issues of cost and time.
On the previous thread this morning, I suggested that I wouldn't want to own a coastal piece of property within 100 miles of NOLA once the pumping operation began.
So, the concrete will sink an inch a year with the rest of the city.
I'm having a really hard time believing these numbers so let me work through the math. The formula for pump horsepower is that it is equal to flow (in gallons per minute) times total discharge head (in feet) divided by a constant of 3960 and pump efficiency. In other words:
Hp = (GPM x TDH in feet)/(3960 x Eff.)
Since the water needs to be pumped a very short distance, I'm going to assume that the TDH is basically the difference in elevation between the 'average' level of where the water is being pumped from to where it is going (Lake Pontchartrain). The entry, discharge and pipe friction losses will be very low. To be conservative, let's say that the TDH is 25 feet. Pump efficiency can be all over the map and as high as say 85% but let's be conservative and say that for the typical pump operating point in this installation, the efficiency is only 60%. The next parameter to work out is power. I may need some help on by someone in LA to refine this a bit but let's assume that the blended electrical cost is $0.10 per kwh (again to be conservative). Based on a typical electrical motor efficiency of 90% and the conversion factor of .746 kW per hp means that one pumping horsepower cost $0.083 per hour to run. This works out to one horsepower costing $0.0014 per minute to run.
Using the earlier formula for pump horsepower and plugging in some of our conservative estimates, moving 1 gpm will require approximately 0.01 hp (1 x 25 divided by 3960 x 0.6). Based on our estimated cost of electricity, this means that the cost to move that one gallon at a head of 25 feet is $0.000014.
Now, all we have to do is take a stab at how many cubic feet of water need to be pumped out. My guess is that your 5,000,000,000 square feet is light. For sake of argument, let's say that there are 25 square miles at a depth of 15 feet. I think that works out to 1.045 times 10 to the 10th power cubic feet. There are approximately 7.5 gallons per cubic foot so this translates into 7.8 times 10 to the 10th gallons. So at the above cost for electricity of $0.000014 per gallon for pumping, this will work out to $1,098,000 to get the job done.
I think your buddy's numbers are way off. If anyone following this has any suggestions on how the numbers can be refined, I will be pleased to run it again with different assumptions (the one that bothers me the most is the estimate of the number of gallons). Sorry about not obeying any round off rules here.
Since you seem to be very familiar with the areas canals, would silt buildup be a problem? Don't know dredging schedules (or who does it) down there. From what I remember of this area from a visit in my youth, the Mississippi and Lake Pontchartrain were pretty "murky" and a good silt buildup in a low/no-flow canal channel will make a 20-foot depth into 10-foot in no time at all. Doesn't hold quite as much water that way.
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