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Author Topic: How can there be water shortages on a planet 2/3 covered in sea?  (Read 9248 times)

Herman Melville

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Hello.

I am new here and have a few questions. I hope these are not ones you are sick of answering.

First off: How can there be water shortages on a planet 2/3 covered in sea? Surely with irrigation and desalination technology there is plenty of water to go round?


 

Offline Chemistry4me

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Not everyone lives by the sea.
 

Herman Melville

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Not everyone lives by the sea.

But if we can lay communications cables around the world, why can't we irrigate deep into continents?
 

Offline Don_1

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You would also need expensive to run desalination plants, and a good series of powerful pumps. I doubt we could run sufficient water for irrigating the deserts and other areas of low rainfall.
 

Herman Melville

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You would also need expensive to run desalination plants, and a good series of powerful pumps. I doubt we could run sufficient water for irrigating the deserts and other areas of low rainfall.

The cost is another matter. If billions can be found to bail out banks or to launch space missions, I'm sure the money could be found.

But in principle, is it possible to irrigate the whole world? It would also resolve the problem of rising sea levels. In fact, it would lower sea levels.
 

Offline Don_1

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No, you would still need immense amounts of power to desalinate and move the water over 1,000's of miles. Turn on your garden hose and try to re-create one hour of medium rainfall, it will probably take you all day (or more).

The amount we could pump out of the sea would have little or no effect on sea levels. Also, any such water would eventually find it's way back to the sea, by rivers, evaporation etc.
 

Herman Melville

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What about building deep canal systems (like underground aqueducts) so that the water flows inland naturally and does not require pumping? The flow of water could also be used to generate electricity.

Apologies for seeming rather stupid. Just curious about these things and delighted to find somewhere that I can ask them!
 

Offline Don_1

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Such an aqueduct would need to start below sea level and continue to fall. It would need to be deep and wide to avoid 'silting up'.

Even at just 1o, by the time you get to 100 miles/k's, it would be too deep to be of much use.

Tucson, Arizona is nearly 400 miles from the Pacific. If your duct dropped at an angle of just 1o, how deep would the reservoir be at the end of the duct?

Quick approx calculation = about 4 miles (I think)!!!
« Last Edit: 02/06/2009 12:39:45 by Don_1 »
 

Offline dentstudent

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Many water shortages are going to occur in regions that are relatively accessible, for example here in Germany. It's really a question of what is meant by "water shortage". It is forecast that there is likely to be a water deficit in summer more frequently with the onset of climate change. The result of this is a reduction to many ecosystems, such as the forests. If these forests don't get enough water, there are many results borne from the die-back of trees and ecosystem dysfunction. Simply irrigating is not going to be a solution to the problem - there is FAR more water required than we could ever put back into the system. Adaption is a much better course - introducing species/provenances that can cope with reductions in water supply, and still maintain ecosystem function. Ultimately, drinking water is extracted from the the ground under these forests, and so it is in our best interests to ensure that the system works.
 

Offline Don_1

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Just to get this tunneling in perspective, the Channel tunnel, linking England to France under the English Channel is 50.5-kilometres(31.4 miles) long and 75 m (250 ft) deep at it's deepest point.

The Seikan Tunnel in Japan is the worlds longest and deepest tunnel at 53.85 kilometres (33.5 miles) long and 240 metres (790 ft) deep at it's deepest point.
 

Herman Melville

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OK, so canals are out of the question.

Could there be a way to manufacture water at the point where it is needed, either chemically or by somehow creating the weather conditions that would allow it to rain in the necessary places?
 

Offline Don_1

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Cloud Seeding http://en.wikipedia.org/wiki/Cloud_seeding

Of course, you need clouds to seed in the first place!
 

Herman Melville

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Cloud Seeding http://en.wikipedia.org/wiki/Cloud_seeding

Of course, you need clouds to seed in the first place!
Could clouds themselves be generated?
 

Offline Don_1

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There are probably enough clouds being produced as it is. The problem is that they don't go where we could use them for the purpose of irrigating the more arid areas. Air streams, hot & cold ocean currents, hot and cold land masses, mountain ranges etc dictate the direction they will take.
 

Herman Melville

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There are probably enough clouds being produced as it is. The problem is that they don't go where we could use them for the purpose of irrigating the more arid areas. Air streams, hot & cold ocean currents, hot and cold land masses, mountain ranges etc dictate the direction they will take.

OK, so it looks as though pumping water is the only solution. Even if it's slow and expensive, I can't see why it's not possible.
 

Offline Don_1

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Desalination plants currently produce less than 0.1% of the world's drinking water. The cost is said to be $325 per year for one average household. The latest plant in Saudi Arabia cost US$3.8 billion and will produce only enough water for the eastern province.

The World Wildlife Fund has said, "Desalinating the sea is an expensive, energy intensive and greenhouse gas-emitting way to get water. It may have a place in the world's future freshwater supplies but regions still have cheaper, better and complementary ways to supply water that are less risky to the environment."

Desalination also causes damage to the coastal environment, such as concentrated salt streams, and a US study reported 55,000 invertebrates and 78,000 fish killed per year in the intake process. I'm afraid I don't know which plant this study was based on, but I should imagine the kill rate will be much increased by the larger plants.
 

Offline Madidus_Scientia

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Water desalination uses a hell of a lot of energy, which usually means more greenhouse gases into the atmosphere, which just exacerbates the problem. If you could build a LARGE solar plant and use the heat to directly boil the water to condense it that would be pretty rad though. Since you only need them where there's no water anyway there shouldn't be any clouds getting in the way of the power :)
« Last Edit: 02/06/2009 17:36:58 by Madidus_Scientia »
 

Offline Bored chemist

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We don't have a shortage of water; we have a surfeit of people.
 

Offline Madidus_Scientia

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Well we could use the solar plant to incinerate people then :p
 

lyner

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Such an aqueduct would need to start below sea level and continue to fall. It would need to be deep and wide to avoid 'silting up'.

Even at just 1o, by the time you get to 100 miles/k's, it would be too deep to be of much use.

Tucson, Arizona is nearly 400 miles from the Pacific. If your duct dropped at an angle of just 1o, how deep would the reservoir be at the end of the duct?

Quick approx calculation = about 4 miles (I think)!!!

If you use a closed pipe, you don't need a constant slope. As long as the inlet is higher than the outlet, you'll get a flow of water. A few tens of metres of height difference would produce a useful pressure. You wouldn't want the lower reservoir to be too deep, in any case, 'cos you'd have to pump the water up to use it!
 

Offline Don_1

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Such an aqueduct would need to start below sea level and continue to fall. It would need to be deep and wide to avoid 'silting up'.

Even at just 1o, by the time you get to 100 miles/k's, it would be too deep to be of much use.

Tucson, Arizona is nearly 400 miles from the Pacific. If your duct dropped at an angle of just 1o, how deep would the reservoir be at the end of the duct?

Quick approx calculation = about 4 miles (I think)!!!

If you use a closed pipe, you don't need a constant slope. As long as the inlet is higher than the outlet, you'll get a flow of water. A few tens of metres of height difference would produce a useful pressure. You wouldn't want the lower reservoir to be too deep, in any case, 'cos you'd have to pump the water up to use it!

Good grief!!! What on earth was I thinking???

Of course you are right! It would have to be an enclosed pipe or half the water would evaporate before it got to the reservoir. So if the inlet was set at 2m below sea level, the outlet need only be 5m below sea level.

I shall stand in the corner for half an hour.

 

lyner

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For a really long pipe, you might need more of a drop in order to get a decent flow rate.
 

Offline Bored chemist

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Any minute now someone will rediscover the Roman technology called a pipe.
Desalination is too expensive for most of the world's population and they don't live somewhere that you could pipe fresh water to.
Even the UK has problems supplying water to its population. OK, most years we get by but don't forget the water we import as goods from other places. Consider how much water was used to grow the crops we import from elsewhere (often from places that don't have water to spare).
What we need is a smaller population or a better source of energy. Maybe a lot of solar powered stills in the hot desert regions would work, but the world would need to sort out its political differences first.
 

Offline jgand

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Our technology is still relatively basic and this is a vast planet. It takes money and resources to get things done. And not everyone is in a sharing mood. In short we have a lot to improve on.
 

Offline Don_1

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Consider how much water was used to grow the crops we import from elsewhere (often from places that don't have water to spare).


Very good point BC.

And not everyone is in a sharing mood.

Quite so. Look back in our history and we find wars fought over water holes. Today it's more likely to be oil and gas which cause these wars, but I predict that, unless there is a drastic reduction in the human population and a concerted effort to settle our differences, we will be back to 'water wars'.
 

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