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According to calculations in "The Australian sea" idea (linked), flooding Lake Eyre would lead to the production of over 16 tonnes of dry salt per second. Now, that's a lot of salt. What could we use it for?
Well, I propose to increase the amount of land available. Firstly we choose a coastal target
area with desirable characteristics for human inhabitation, no important ecological zones and ideally a relatively shallow ocean nearby. Luckily the first two requirements are likely to co-vary, since any desirable areas for humans will already be inhabited, and hence any wildlife is already buggered.
Now, let us assume that our inexhaustible salt spigot is turned on, and the salt can easily be transported somewhere very nearby. In the case of Australia, Eyre is flooded, with very salty concentrated water run to a second, much smaller evaporating basin somewhere near the coast. Salt is scraped out of there for use in the project, as well as for any other profitable purposes.
To reclaim land from the sea, the traditional approach is to build a dyke around a bit of sea, pump the water out and call it land. However, one disadvantage of this is that the new land is still below sea-level. If a dyke fails the area is flooded. So my proposal is to add an extra step:
The old sea-bed would be scraped up, to whatever depth is desirable to provide useful soil for the new land and according to the geology. Probably 3 metres or so would be ample. Salt would be packaged in large water-proof bags and laid down, compressed and, once a suitable height above sea-level is attained, covered with a protective layer and buried by the rocks and soil.
Once a large area has been reclaimed in this way, some sections could be left un-raised. These could then be used to increase the evaporation area and bring their final product (ie, salt) closer to the work area. A big advantage of this is that this area is below sea-level, so no pumping is necessary.
Now, there are at least some potential concerns. There is obviously a large requirement for strong water-proof material. I imagine this would probably be plastic - although potentially it could be recycled plastic unsuitable for other purposes. The demand can be minimised by increasing the volume of the bags, although I imagine there is a trade-off between making the bags larger and increasing the potential loss if a bag is burst or punctured somehow.
The land above the salt may not be particularly stable - salt is not renown for its strength in compression, and settling may occur for some time. However, it should be fine for crops. Where buildings are planned no salt need be used - an area nearby can be dug to a much greater depth, and the rock transferred to the target area.
There would also be some loss of littoral zone habitats. This may be mitigated by building small islands or other structures in less-desirable deeper areas, using some of the material removed before salt emplacement.
The Australian sea
The_20Australian_20sea
now there's no excuse not to. [Loris, Apr 08 2010]
The chemical composition of seawater
http://www.seafrien...awater.htm#salinity
see the box 'Making sea salt'. [Loris, Sep 26 2010]
Death Valley
http://phobos.ramap...r/SW04/Jan07BW.html
note how far below sea level it is (first picture) :D [FlyingToaster, Sep 28 2010]
Sinkhole
http://scribalterro...es/guatsinkhole.jpg
This happens when bugs and the environment cause tears, letting the salt wash out. [Voice, Sep 28 2010]
[link]
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//What could we use it for?//
jump-starting the Gulfstream haline pump ? |
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A thick bed of clay over the salt will mean you can cut down on the waterproofing needed. |
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Very big bags .... remember, surface area to volume, square to cube ratio. |
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//Very big bags .... remember, surface area to volume, square to cube ratio.// |
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Yes. But unfortunately, only up to a point.
I was maybe a bit cryptic in how big the bags would be, because I don't have data on what would be suitable. But since we're going to be laying down a layer of a certain thickness, this puts a limit on at least one of the dimensions. Unless one excavates one area to provide material for another, which would involve its own work of course. |
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On the other hand, it occurred to me that a slightly different method would involve sealing the salt into a bag in-situ. This can only work if conditions allow the last bit of drying to occur on-site. Then one could do much less work and get a denser salt layer. A plastic sheet (or some other water-impermeable layer) would be laid down over as large an area as possible, then salt-water pumped in. After a salt layer of sufficient depth built up and the water has been baked off, another sheet of plastic would be laid on top. Then all that has to be done is seal round the edge. I think one could make acre-sized bags in this manner. |
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Some calculation on the 'dry in-situ' approach - how fast could we build up usable land? |
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According to a graph in Wikipedia, the solubility of salt is something over 35% at 0 degrees C (that is, 35 g per 100 mls fluid). (That rises slightly with temperature.)
So let us suppose we receive salt-water at 35g per 100 mls. That is around 10 times more concentrated than sea-water.
So assuming we can arrange for the same conditions, the remaining water should be driven off in less than a tenth of the time (35g in 1000 mls to 35g in 100mls removes 900 mls water; to get from there to 35g solid salt will be less than 90 mls water).
Thus a 10 metre thick layer generated in 40 years (following on from BunsonHoneydew's calculations on 'The Australian sea').
Starting out at the seashore, even half that should be ample, so only 20 years would be required for final land to be formed. In practice, one would probably want to start out dredging down at least to bedrock, providing a large amount of material with which to build subsequent dykes with, and a stable target pond for future areas to draw from in the next stage. |
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Admittedly, 20 years is still a bit of a long time. However, there are intermediate options.
Suppose we use the initial suggestion of a large, shallow drying area nearby the region to be resurfaced. Damp salt can be continuously harvested and transported to the target area. |
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It may be possible to persuade this salt into a solid, void-free form like the in-situ rocksalt. The naive method is just to attempt to compact it together using steamrollers or similar. That may or may not work - it might get the air out, but also smash the crystals to powder, reducing cohesion. Maybe Ostwald ripening would repair the damage in a suitable time-period.
Alternatively, maybe the target area could be flooded with salt solution either periodically or continuously - with the damp salt spread over it in layers from time to time. This will increase the local accretion rate, and perhaps retain the desirable void-free, large crystal rock formation. I don't know enough about the dynamics of this to say any protocol would work, but there are interesting processes involved. |
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//fine for crops// Wait, what? |
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According to a webpage I found recently (see link "The chemical composition of seawater") it may be a bit more tricky than my above annotation suggests. |
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Basically the non-water ingredients of sea-water precipitate out in order as the water is reduced: |
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//... Between 100% and 50% first the calcium carbonate (CaCO3= limestone) precipitates out, which is chalk and not desirable. Between 50% and 20%, gypsum precipitates out (CaSO4.2H2O), which also tastes like chalk. Between 20% and 1% sea salt precipitates (NaCl) but going further, the bitter potassium and magnesium chlorides and sulfates precipitate...// |
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This doesn't completely preclude the in-situ setting idea, however, it would need a little tweaking:
Most obviously, we'd only be able to evaporate the water down to 20% [1] before salt started precipitating. This difference is presumably down to interactions with the other ions in solution. This would approximately double the amount of water needing to be evaporated in-situ.
Fortunately, there isn't that much calcium in the seawater compared to sodium and chlorine.
If my calculations (based on values given in a table on the same page) are correct NaCl alone is 3% of seawater by weight [1 again]. If we assume that all the calcium comes off as gypsum (CaSO4.2(H2O)), then it makes up 0.18%. In reality it must be less than that, since limestone shares the calcium (which is limiting) and is lighter per mole, and there are other salts precipitating out after NaCl. So we'd silt up the inland sea with limestone and gypsum at something under one sixteenth as fast as we could build up new land. Again, not necessarily a deal-breaker - if we segmented the inland sea appropriately we'd be able to purify these two compounds and mine them for other purposes when they'd built up to a sufficient depth. |
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[1] I should note that the percentages in the quoted passage obviously differ from standard practice[2]. I think they are talking about percentage of liquid water remaining from the original volume. |
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[2] weight per volume. A 1% solution has 1 gram of solute per 100 ml of the solution. |
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// //fine for crops// Wait, what?// |
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I mean - why do you have a problem with that?
I'm suggesting that we generate new areas of land which would be a few meters above sea-level - building up the ground with a layer of salt, sealing it off so it doesn't leach away, capping it off with a few meters of soil, and using it for agriculture. |
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Never mind, on first reading, I missed //covered with a
protective layer and buried by the rocks and soil.// Sorry. |
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Oooh, that's too good not to use. Thanks! |
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If you worked it right, you could easily get the salt to form in slabs, not loose crystals. You could cut and transport slabs, or just evaporate the salt in layers on-site. |
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That would simplify handling, reduce the need for bags, reduce settling and make life easier. (I think salt evaporates out as crystals that coalesce into slabs, getting it into shaker-sized crystals requires a lot of scraping.) There are salt mines in many places that demonstrate how strong slab salt is, with pillars and all. The Hutchison area of Kansas is underlain by salt layers, and nobody worries about that until humans let water in. |
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Once the slabs are in place, any system to reduce water flow would keep them from melting. If some water got in, it would saturate with salt and stop dissolving any more. Only a tidal flow in and out is to be worried about, or rain draining off. |
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I'd build a dike, pump in seawater, evaporate and repeat for for a few years, cap the salt slab with clay, plastic, concrete or asphalt or buildings, and spread soil if desired. Then keep an eye on the dike. |
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If you are going to spread soil and run a normal farm with irrigation, you will need to watch your water to avoid drainage problems. I recommend hydroponics, tourism, manufacturing or something else that is dry. |
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Couldn't you just make bricks and build buildings and things ? I don't really like the idea of a game of Tetris being played under my south 40 when the bags break. |
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Say, if you want to get some granular stuff out of the ocean, and build land with it, without worrying about it dissolving, you could just dredge up sand. Which is what they are doing in Dubai. |
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Pumping up water just to get the salt out is going to waste a lot of pumping--what, forty tonnes of water for one tonne of salt? Then there's all the evaporation time, the bagging and the worries about rain. |
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Sand, sucked up by a water dredge, is probably hoisting around two tonnes of water for a tonne of sand. So there's efficiency there. And it only takes minutes for the water to drain out. And sand doesn't dissolve, though it will wash away. |
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I like the salt idea, but it's pretty close to using sand, except worse. Sometime it will work out, so I'm keeping my salty croissant up there. |
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//According to calculations in "The Australian sea" idea (linked)// |
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I can't imagine a worse source than calculations in a bakery idea. |
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Salt does have the advantage of being capable of forming a solid layer, as you say, baconbrain.
The problem with using sand is that the further from shore you get, the more you need, and the further away you need to bring it from. You can't take too much from nearby because it will tend to settle back into place. Conversely, with the saltwater methods the lower down you get the less pumping you need to do - anything below a certain height won't need pumping at all.
On the other hand, if sand is available in large quantities, it could be used as part of a thicker fill above the salt layer, to reduce the risk of puncture by human activity - or even mixed in with the maturing salt if that improves characteristics like structural strength. |
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The Dubai developments are designed to greatly increase shoreline, so salt wouldn't be a good fit for them. They're working in fairly shallow water, and still use boulders to line the outside walls and protect the delicate foundations of the new islands/peninsulae. |
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If the salt is sealed and buried as I propose I don't think there is any great worry about leakage. I suggest that there is less risk of catastrophic failure than with sub sea-level land. |
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I didn't worry about the reliability of the salt yield calculation - I don't think the salt supply would be the limiting factor! |
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Unprotected salt will inevitably leech into the ground
water. Protected salt will too, with varying levels of timeth. |
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//Unprotected salt will inevitably leech into the ground water. Protected salt will too, with varying levels of timeth.// |
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Surprisingly large areas of land (and sea) are underlain by long-lived beds of halite. For example, in the UK (a land not renown for minimal rainfall) there are three significant rocksalt mines, harvesting material laid down 220 million years ago.
While what you say is true, the timescales involved clearly are at least potentially way beyond human timescales. |
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