Risk: An Allegory

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Here’s an interesting article on CNBC’s website: Katrina anniversary: Will New Orleans levees hold next time?

The 100-year threshold is also a statistical guess based on data on past storms and assessments of whether they’ll occur in the future. That means the models change every time a new hurricane strikes. The numbers being used as guidelines for construction are changing as time passes.
 
The standard also does not mean—can’t possibly mean—that a 100-year storm will occur only once per century. It means that such a storm has a 1 percent chance of happening in any given year. So for example, it’s technically possible for several 100-year floods to occur in just a few years, although it’s highly unlikely.

One way to look at it is that the engineers need to estimate how high a wall New Orleans needs to protect itself against a reasonably unlikely flood — say, a 1-in-1000-year event. This is the line of discussion pursued in the CNBC article.

Another way to look at it is to observe that the odds of another Katrina, or worse, within a specified period are highly uncertain. In this case a radical course of action might be called for. You do something like: take the best estimate for the wall height needed to protect against a 1000-year flood and then double it. Building such a levee would probably be extremely expensive but at least the costs would be out in the open. Or you might decide that it’s not the best idea to have a coastal city that’s below sea level, and so you would discourage people from moving back to New Orleans, rather than encourage them by subsidizing a new and stronger system of walls.

In this kind of situation the political incentives are usually going to encourage public decisionmakers to ignore radical solutions with high obvious costs, in favor of the minimum acceptable incremental solution with hidden costs: probably subsidies to rebuild the levees to, or perhaps a bit beyond, the standard needed to protect the city in the event of another Katrina. And it’s unlikely that any local pol is going to advise residents to move out and depopulate his constituency. Thus, eventually, a worst case will probably happen again.

14 thoughts on “Risk: An Allegory”

  3. Once they finished MRGO the table was set for disaster. The Mississippi Delta was protecting the city and the channel cut right through the swamps and left a big hole. The levees and the corruption helped but MRGO was the worst decision.

    Ivor Van Heerden, also well-known critic of the Army Corps of Engineers who led the state’s investigation into Katrina failures, said new computer modeling done over the last 12 to 18 months also proves that one mile of healthy wetlands can reduce storm surge by one foot.

    “That’s more (reduction) than we’ve known before,” he told Southeast Louisiana Flood Protection Authority-East members.

    “I’ve seen a recent paper that says wetlands have no value … and I’ll be using this modeling and some old (science) to counter that,” he said.?

  5. “Is there any continuing purpose served by having a city there?”

    Seeing that there is the mouth of the Mississippi River, then yes you need to have a city there to maintain the sixth busiest port in the US. Additionally the port also serves as the hub of much of the offshore oil industry of the Gulf of Mexico.

    The real question is what kind of city do you want to rebuild in the location? Seeing that the modern container port doesn’t need an army of stevedores that use to work in the holds loading and unloading loose cargo. A rebuilt city with a smaller population is what is needed now. That way you could leave the lowest elevation sections of the city, like the Lower 9th Ward, as parkland and concentrate the reconstruction for remaining population in the higher elevation areas.

    Then again that raises issues of property rights of the land owners in the lower elevation areas, but that’s another debate.

  6. Now that Louisiana has some honest government, there might be some hope for improvement. There are cities on the Mississippi farther north that were moved from the river bank to higher ground. Many NO residents moved to Texas after the storm and I believe not all have returned. It might be possible to build a new city on higher ground but I am not that familiar with the environs so would defer to geologists. I’ve been there but only for short visits.

    The Army COE has been a very bad influence as it has been in other places. Remember that Galveston was the big Texas port until the hurricanes destroyed it early in the 20th century. That led to the ship channel to Houston. NO has history but it is expensive history.

  8. The solution is amortization.

    Expect that nothing lasts forever. Just guess at how long one can reasonably expect to get useful return out of one’s investment.

    That said, NO only needs a WORKING population. As a place to warehouse welfare recipients, it is no worthwhile. But then who wants them except Democratic mayors?

  9. ” As a place to warehouse welfare recipients, it is no worthwhile. But then who wants them …”: couldn’t they be given the abandoned housing in Detroit?

  10. Dearieme-Prior to modern times the Mississippi had no mouth. Rather it ended in a huge delta. That’s one reason DeSota couldn’t find it. The present course of the Mississippi to the sea exists only as a result of human intervention and is highly unstable. The location of New Orleans is probably less dangerous than the location of Naples but it is nevertheless asking Nature to kick you in the teeth. Galveston is pretty bad too but it’s a lot easier to get out of Galveston.

  12. The Corps has over time blocked all of the Mississippi outlet except 2 – the current main channel past NO and the Atchafalaya, which runs by Morgan City and currently takes around 1/3rd of the flow. If not for a large “control structure”, the Atchafalaya would already be the main outlet, as the NO outlet is much higher.

    If you are interested in the subject, “The Control of Nature” by John McPhee has a section on this (along with one on the LA wildfire/mudslide cycle and another on Iceland). Typical McPhee (meaning excellent), quite worthwhile if you are interested in the subject.

  13. Also – historically floods in New Orleans were from the river, not the Gulf. The destruction of much of the delta due to a combination of dredging connected to oil production and subsidence as a consequence of flood control projects dumping all the river silt into the Gulf instead of the Delta has removed most of the coastal buffer that used to absorb tropical storms.

    Major river deltas are not where you want to build cities – they are simply too unstable to expect a single location to last for centuries. The major city in LA should really be at Baton Rouge (more or less anyway).

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