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Louisiana’s Governor Declares State Of Emergency Over Disappearing Coastline

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Re: Louisiana’s Governor Declares State Of Emergency Over Disappearing Coastline

#121

Post by snowwrestler »

hyperpape wrote: post #94
OliverJones wrote: post #39

Earlier quoted context omitted.

Thirty years ago, John McPhee wrote about this very issue. At that time a ship on the Mississippi river could go through a lock, drop FIFTY FEET, and take a shortcut to the ocean via the Atachfalaya river. http://www.newyorker.com/magazine/1987/02/23/atchafalaya Just because it's not a new situation doesn't mean it's not an emergency.

Can someone explain the following bit from that article to me: "As the mouth advances southward and the river lengthens, the gradient declines, the current slows, and sediment builds up the bed. Eventually, it builds up so much that the river spills to one side." I'm having a little trouble understanding it. What does it mean for the mouth of the river to move southward? Does sediment build up and create new land nea…

Sediment carrying capacity in water is affected by current speed. Even a slow moving river slows down when it hits the ocean. Then the sediment it is carrying settles out to the bottom.

Over time this creates an underwater mound that acts like a barrier to the current. So it deflects to one side or the other (or both). Then the sediment builds up in that new location until the current deflects again.

Over time this builds up a fan-shaped extension of the shoreline called a delta. The river might flow out through any number of channels through the delta, and it might change often.

The bigger the river, the bigger the delta. The Mississippi has a huge one... which New Orleans sits on top of.

Re: Louisiana’s Governor Declares State Of Emergency Over Disappearing Coastline

#122

Post by sizzzzlerz »

snowwrestler wrote: post #121
hyperpape wrote: post #94

Earlier quoted context omitted.

Can someone explain the following bit from that article to me: "As the mouth advances southward and the river lengthens, the gradient declines, the current slows, and sediment builds up the bed. Eventually, it builds up so much that the river spills to one side." I'm having a little trouble understanding it. What does it mean for the mouth of the river to move southward? Does sediment build up and create new land nea…

Sediment carrying capacity in water is affected by current speed. Even a slow moving river slows down when it hits the ocean. Then the sediment it is carrying settles out to the bottom. Over time this creates an underwater mound that acts like a barrier to the current. So it deflects to one side or the other (or both). Then the sediment builds up in that new location until the current deflects again. Over time this b…

For now, any way

Re: Louisiana’s Governor Declares State Of Emergency Over Disappearing Coastline

#123

Post by ska »

hackuser wrote: post #118
evilduck wrote: post #78

Earlier quoted context omitted.

I lived in LA for several years. Global warming is a factor in receding coastlines worldwide, but on this particular coastline it's a very small factor relative to the complete mismanagement of waterways and marsh ecosystems. As it goes on, rising sea levels will play a bigger role in a large part of Louisiana disappearing, but right now the crisis is a different man made disaster. 20cm over a century is practically…

> I lived in LA for several years. I'm not sure how that informs you on the cause.

I suspect LA is short for Louisiana, not Los Angeles, in this context.

Re: Louisiana’s Governor Declares State Of Emergency Over Disappearing Coastline

#124

Post by ska »

hackuser wrote: post #119
adolph wrote: post #29

The first two comments seem to associate anthropogenic climate change with the changes in Louisiana's coastline. A more likely culprit is hydrologic mismanagement. The coastline was formed by waterways that periodically changed channels and dumped sediment in different areas. In relatively recent times cities on the existing waterways became politically influential enough for the federal government to build a series…

> The first two comments seem to associate anthropogenic climate change with the changes in Louisiana's coastline. A more likely culprit is hydrologic mismanagement. What is that based on?

for an overview see, e.g. http://www.mississippiriverdelta.org/files/2011/11/map-100-y...

There is a pretty wide literature on this also.

Re: Louisiana’s Governor Declares State Of Emergency Over Disappearing Coastline

#125

Post by bluetwo »

hyperpape wrote: post #94
OliverJones wrote: post #39

Earlier quoted context omitted.

Thirty years ago, John McPhee wrote about this very issue. At that time a ship on the Mississippi river could go through a lock, drop FIFTY FEET, and take a shortcut to the ocean via the Atachfalaya river. http://www.newyorker.com/magazine/1987/02/23/atchafalaya Just because it's not a new situation doesn't mean it's not an emergency.

Can someone explain the following bit from that article to me: "As the mouth advances southward and the river lengthens, the gradient declines, the current slows, and sediment builds up the bed. Eventually, it builds up so much that the river spills to one side." I'm having a little trouble understanding it. What does it mean for the mouth of the river to move southward? Does sediment build up and create new land nea…

It makes more sense if you understand the old/new river formation and how they create one another (and oxbow lakes).

Here is some more info.

http://cbsd.org/cms/lib010/PA01916442/Centricity/Domain/1622...

Re: Louisiana’s Governor Declares State Of Emergency Over Disappearing Coastline

#126

Post by hackuser »

ska wrote: post #123
hackuser wrote: post #118

Earlier quoted context omitted.

> I lived in LA for several years. I'm not sure how that informs you on the cause.

I suspect LA is short for Louisiana, not Los Angeles, in this context.

I figured. My point is that locality doesn't inform you on whether the coastline is receding due to climate change. Do people in Los Angeles know the causes of their droughts, simply by virtue of living there?

Re: Louisiana’s Governor Declares State Of Emergency Over Disappearing Coastline

#127

Post by adolph »

splawn wrote: post #107
MisterBastahrd wrote: post #103

Earlier quoted context omitted.

You're being condescending. Everyone in the area knows that the main culprit in losing coastline isn't AGW but the taming of the river, essentially dumping sediment that used to build the delta over the continental shelf, and all the channels cut into the marsh.

My apologies, I didn't mean to be condescending. However, It is a fact that sea level rise is a large factor in this, even if it is not the "main culprit". Most people in that area rely on the oil industry either directly through employment or indirectly through the local economy so they tend to have a blind spot when it comes to AGW, which is completely understandable.

If sea level rise were a seriously contributing factor to the Louisiana coastline problem then other Gulf coast states with similar topography (Alabama, Florida, Mississippi and Texas) would have a similar emergency. As far as I can tell, they don't to the same extent. How would you explain that sea level rise affects Louisiana more than other Gulf coast states?

Re: Louisiana’s Governor Declares State Of Emergency Over Disappearing Coastline

#128

Post by ItsDeathball »

delinka wrote: post #21
criley2 wrote: post #8

Earlier quoted context omitted.

Actually when you consider the global implications of climate and the local effects of shore, a local area using local money to protect local shore in the face of global inaction they are powerless to change makes perfect sense. It is actually your position which makes no sense. "Hey 4.6 million Louisianans, sure you're only 0.00063% of world population, but protecting yourself and your land from what the other 99.99…

And what about moving industry and residences away from the current coastline over the next 50 years? Make a plan to prevent new real estate development within a certain distance of the current coast; plan the obsolescence of currently developed areas and over time reclaim them for the environment.

That's a problem when the coastline is the reason for those industries and residences being there. It's not exactly feasible to relocate the oil refining and shipbuilding industries of New Orleans and Baton Rouge to central Mississippi.

Re: Louisiana’s Governor Declares State Of Emergency Over Disappearing Coastline

#129

Post by splawn »

adolph wrote: post #127
splawn wrote: post #107

Earlier quoted context omitted.

My apologies, I didn't mean to be condescending. However, It is a fact that sea level rise is a large factor in this, even if it is not the "main culprit". Most people in that area rely on the oil industry either directly through employment or indirectly through the local economy so they tend to have a blind spot when it comes to AGW, which is completely understandable.

If sea level rise were a seriously contributing factor to the Louisiana coastline problem then other Gulf coast states with similar topography (Alabama, Florida, Mississippi and Texas) would have a similar emergency. As far as I can tell, they don't to the same extent. How would you explain that sea level rise affects Louisiana more than other Gulf coast states?

Every one of those states you listed are experiencing increased coastal flooding thanks to climate change and yes that flooding damages marshlands.[0]

Nowhere have I claimed that the issue in LA is solely AGW.. only that the sizable portion of the problem that is caused by AGW is going to fall on deaf ears in that region because of the amount of oil money there.

[0]http://www.evergladesfoundation.org/2016/10/14/this-weeks-ki...

Re: Louisiana’s Governor Declares State Of Emergency Over Disappearing Coastline

#130

Post by adolph »

hackuser wrote: post #119
adolph wrote: post #29

The first two comments seem to associate anthropogenic climate change with the changes in Louisiana's coastline. A more likely culprit is hydrologic mismanagement. The coastline was formed by waterways that periodically changed channels and dumped sediment in different areas. In relatively recent times cities on the existing waterways became politically influential enough for the federal government to build a series…

> The first two comments seem to associate anthropogenic climate change with the changes in Louisiana's coastline. A more likely culprit is hydrologic mismanagement. What is that based on?

Well, I wrote mismanagement this morning and have spent more time reconsidering the topic since. I'd guess that if people knew then what they know now, they'd do things differently or not do them. Using the word mismanagement is an unfair criticism.

If the coastline changes were significantly caused by climate change/rising sea levels then the other Gulf coast states would have problems too. The link between the control humans have exerted on Louisiana rivers, additional artificial waterways and loss of coastline is fairly well established. If you'd like more information, the below medium work seems a reasonable introduction--I scanned over it and it seems to have the main points, some nice maps, doesn't avoid the problem of sea level changes, and has some human interest stuff:

https://medium.com/matter/louisiana-loses-its-boot-b55b3bd52...

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