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Comment by kj4211cash | Hacker News Reader

Oh hey, something I used to work on. The story here is coastal erosion / land subsidence much more than it is sea level rise, although that is a contributing factor. The land subsidence has been caused by Engineering works of the past, including the construction of levees and floodwalls around the city. When I worked on this a decade ago, we were already telling people outside of the city to move and spending a fortune to protect people inside the city. The most cost-effective option is often getting people to move, but good luck convincing everyone. Also this is such a shame because New Orleans is one of the most unique, charming places in the US.

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Didn't the governor famously cancel coastal restoration programs?

Yup. The article mentions this, briefly.

New Orleans is on a river delta, and without human effects on land, and without sea level rise, wouldn't one expect this delta to expand due to silt deposition?

And would this silt deposition actually occur at a rate that would fully counteract sea level rise, just as the huge rise in sea levels at the end of the last ice age did not mean that the delta disappeared?

If so, the danger to New Orleans would be entirely avoidable by changes in local land use.

Perhaps the fundamental issue is that river deltas tend to be dynamic, with the watercourse continually changing, which isn't really compatible with a city in a fixed location. (Hence the damaging attempts at stopping this.)

Hmmm... On the one hand, yes, silt deposition would tend to expand the delta and that's what you saw over the last 5,000 years up until the 1930's. And yes, it was work done by the Corps of Engineers to fix the course of the Mississippi River that broke this system. That plus logging, oil and gas extraction, and tons of other "local land use" things then led to sinking ground levels. As the article mentions, the governor cancelled a(n expensive) effort that would have resulted in more silt deposition ... in the general area that most experts think would have helped.

On the other hand, the silt wasn't ever being deposited in large quantities in New Orleans itself, but more in other places. The delta is huge. New Orleans is famously below sea level and always has been. There's always been hurricanes. It's always been dangerous to live there and I'm not sure you can blame the dynamic nature of the river.

It isn’t expansion that it would do it is a return to wandering. When a river wanders, typically people die. It is not a good thing to be near a wandering river.

The river water picks up silt as it flows to the sea. The silt has to go somewhere. That's why the delta exists, and grows, absent other effects.

The river wandering is part of this. Since the silt can only be deposited where the water goes, for the delta to grow (or just maintain itself) the river has to go here and there all over it.

And yes, people die when this happens. But if you stop the river wandering, the silt isn't going to be deposited so as to maintain the delta.

Maybe it's not a good location for permanent human settlement.

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