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No mention of the cause: Diverting the Mississippi River. In the 20's / 30's The Army Core of Engineers built a series of levees to redirect the Mississippi to
by _red 9y ago
No mention of the cause: Diverting the Mississippi River. In the 20's / 30's The Army Core of Engineers built a series of levees to redirect the Mississippi to flow east of its natural course. Before then, the river would seasonally shift back and forth (think of the end of a garden house spraying left and right).
It naturally wanted to flow into the Atchafalaya Basin, instead all the silt and sand that would've gone into building the wetlands is being diverted and dumped directly into Gulf.
Look at a map sometime and you can clearly see it, the "toe" of Louisiana (south of New Orleans) is growing out into the gulf, this is the trillions of tons of silt and sand. Meanwhile the "heel" is shrinking, as the Gulf slowly erodes it.
Note: This is not an anti ACoE diatribe. Its just that anytime this story gets national coverage they fail to mention the cause, which is locally well known and well understood.
- clebio 9y agoJohn McPhee wrote about this. Not everyone forgets. https://en.wikipedia.org/wiki/The_Control_of_Nature https://en.wikipedia.org/wiki/The_Control_of_Nature
- theoh 9y agohttps://www.newyorker.com/magazine/1987/02/23/atchafalaya https://www.newyorker.com/magazine/1987/02/23/atchafalaya
- bilbo0s 9y agoThe issue is that, even under your ideal scenario, where the Mississippi flows into the Atchafalaya Basin... we'd still be evacuating, we would just be evacuating that area instead. This is a problem for EVERY port, and coastal area, that we built below sea level. As the sea level rises, a new reality takes shape. There's nothing particularly novel about Louisiana in this regard. In fact, that's the entire reason we hope to use the Louisiana experience as a blueprint for our plan of action in other areas.
- _red 9y ago>ideal scenario I'm not actually advocating one way or the other. Its understandable why the ACoE did what they did. I'm simply saying this is the result of that decision.
- jessriedel 9y agoThey do mention a cause in the article: "...due to a mix of rising seas and sinking land caused in part by oil and gas extraction". I don't know anything about this topic, but I'd wager that since your explanation is boring and the one chosen by Bloomberg is vague, politically charged, and hedged, that you're more likely to be correct.
- cossatot 9y agoGeologist here: while overly managing of the Mississippi does make a difference, that only controls where new sediment gets deposited. Even if new sediment was deposited in sinking urban areas, it wouldn’t ameliorate the problem of subsidence because it would be deposited on existing infrastructure, burying it. The real reason for the subsidence is that the sediment that makes up river deltas slowly compacts under its own weight, expelling pore water and becoming more dense. This is natural and unavoidable, although it might be marginally enhanced by oil and gas extraction (it is a bigger problem with groundwater withdrawal in other areas).
- specialist 9y agoYou’re the expert, but I thought subsidence (land sinking because of fossil fuel extraction) and compaction were two different phenomemons. Plus erosion (loss of coastline) and rising ocean, there’s multiple factors involved.
- cossatot 9y agoThey are related phenomena. Basically, sand and mud have pore space in between the grains that is filled with fluids (water, oil or gas). When those fluids are extracted, the rock contracts because the pore pressure decreases, causing an increase in density (compaction) and a decrease in volume, which leads to subsidence. Some of this is recoverable, and some of it isn't, because the grains will find a more efficient packing arrangement. You are completely correct in that there are many different factors involved that are all causing problems; unfortunately they are all interrelated.