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Still Waters

Megacities contend with sinking land

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Subsiding land is a bigger immediate problem for the world's coastal cities than sea level rise, say scientists.

In some parts of the globe, the ground is going down 10 times faster than the water is rising, with the causes very often being driven by human activity.

http://www.bbc.co.uk...onment-27202192

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Well now everyone wants to be like New Orleans. :P

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This should be the headline...

People find out their actions have consequences shock!

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New Orleans and Venice seem to me to be hopeless cases; they need to get the art out of there.

Ho Chi Minh City stopped allowing people digging their own wells several years ago; I thought it was probably a health measure but maybe this has something to do with it.

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My understanding of the problem of New Orleans is that the delta created by the Mississippi River has been shrinking, that the thousands of acres of marsh grass (probably Spartina and others) have been receding from the Gulf. I am not sure if this is due to changes in salinity by diverting some of the river, or pollution such as phosphate runoff from agriculture or even damage from the BP oil spill, but these acres of grass used to help protect NO from the storms and hurricanes that plague the Gulf of Mexico. As they die off the Gulf moves ever closer to the city which is then exposed to direct threat from these storms. This does not mean that the city is sinking, but that it is more subject to inundation when storms push water toward the coast.

Also I would suspect that in mitigating the flow of the Mississippi, the so-called taming of Old Man River, there has been a reduction in silt deposits to the delta as well and it was this rich silt that formed the soil for the marsh grasses. It is a battle between the river building up the sediment and the Gulf washing it away and we have changed the equilibrium in the Gulf's favor.

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New Orleans and Venice seem to me to be hopeless cases; they need to get the art out of there.

Ho Chi Minh City stopped allowing people digging their own wells several years ago; I thought it was probably a health measure but maybe this has something to do with it.

New Orleans and Venice were the first ones I thought of too. The Netherlands is next. I don't know which other cities have a low elevation near water.

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You mean to tell me that large cities built next to water are sinking? Poppycock.

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New Orleans has been below sea level for a long time. The levees were built to keep the water out. As nice as the "Big O" is I don't know if I'd want to live in that type of situation.

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New Orleans and Venice were the first ones I thought of too. The Netherlands is next. I don't know which other cities have a low elevation near water.

New York and Tokyo spring to mind. For the most part, subsidence really only affects cities that have been built on reclaimed land that is waterlogged. The weight of the buildings is usually enough to create subsidence, although seismic activity will exacerbate the problem.

Although not a major city by any measure, Christchurch is suffering from a lot of drainage problems due to the earthquakes and the subsidence they created. Properties that would usually flood within a one-in-100 year storm now flood every time heavy rain occurs.

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New Orleans and Venice were the first ones I thought of too. The Netherlands is next. I don't know which other cities have a low elevation near water.

I think the Dutch are dealing with it and will do okay, but it will cost a lot of money. That will probably in the end be the case with the vast majority of cities in wealthier countries. This problem can also be mitigated by stopping the water withdrawal.

Sea Level rising on the other hand will hit places like the Mekong and Ganges and Nile deltas, all heavily populated and without the resources rich countries have, and will need help. I think Ho Chi Minh City and Decca and Alexandria themselves will be okay but there are huge rural populations in those areas at risk.

The situation is similar in China but they have more money.

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