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So, the Mediterranean Empire has succeeded in separating the entire Mediterranean Sea from the rest of the world's oceans. See this question for background and premise. There are now dams making sure no other ocean will flow in.

Related Wikipedia article: Atlantropa.

The motive for doing this is to gain more land-area.

However, the Mediterranean is still full of seawater. How do we get it all out of there?

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  1. I've considered pumping all the water out into the Atlantic and/or Gulf of Suez with thousands of massive pumps. We have lots of nuclear power to power the pumps, or we could even fill the Sahara with solar power plants. We have immense resources and virtually unlimited political will. Could this work? I'd like to see some maths on pumping capacity, electricity requirements, time required, feasibility, et cetera.

  2. How much will natural evaporation help us? This is a humongous project and it's alright to spend several years emptying the whole Mediterranean. Of course, the faster the better. However, if it really needs to take a century, then so be it.

  3. Are there any other brilliant ways to get all the seawater out in years or decades?

  4. What to do with all the rivers that flow into the Mediterranean, counteracting our work?
  5. Are there any very serious challenges I haven't thought of?

No hand-waving allowed. We need scientifically sound explanations. Technology used should be 2016 level. But we should also consider that it's an incredibly resourceful empire which has committed itself considerably to this project and given it a quite high priority.

Please note that while this is indeed similar to Atlantropa, it is not identical to Atlantropa. For example, the Empire intends to drain the whole Mediterranean, not just parts.

Wikipedia suggests the volume of the Mediterranean is 3,750,000 km3.

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  • $\begingroup$ Wikipedia, had you read it, would have also told you that the residence time of water is 80-100 years, and, i cite, "Evaporation greatly exceeds precipitation and river runoff in the Mediterranean". $\endgroup$ – Karl Sep 18 '16 at 23:41
  • $\begingroup$ The answers to this question can be found in 20 minutes on the internet, and you forbid talking about the actually interesting question, why or why not to do that. Add the ridiculous condition that you want to empty it completely, for which you give no reason. And "no fantasy", but you can stop rivers? ;-) $\endgroup$ – Karl Sep 19 '16 at 0:03
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    $\begingroup$ @Marky I definitely second the "less than optimal side-effects" point. $\endgroup$ – Revetahw Sep 19 '16 at 15:22
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    $\begingroup$ @Fiksdal did some quick math (based on reddit.com/r/theydidthemath/comments/2yowyj/…) and resulted with the number of nukes needed to evaporate that amount of water; Hiroshema bombs = 1.44545x10^12(1,445,450,000,000). Tsar Bombs = 9.6363x10^8(963,630,000). $\endgroup$ – Marky Sep 19 '16 at 15:41
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    $\begingroup$ @Marky Haha. That's absolutely bizarre. $\endgroup$ – Revetahw Sep 19 '16 at 15:45
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You must think of three things in parallel, namely:

  1. What to do with the water
  2. How to avoid rivers filling it again
  3. What will happen with the climate

These are a pack; feel free to separate them into your separated questions if you wish, but read them all first.

Number 1 seems easy. If you have the dam, you can have pumps as well. The volume is 'just'‎ 3,750,000 km³ and the biggest real-world pump moves 567.81 m³/s, or 17,906,456,160 m³/y (17.906 km³/y). It is easy to see that one of these takes about 210 thousand years to do the job. The more pumps, the fewer years; now, it's only about how much money to invest.

Evaporation will diminish in importance as the area reduces. Also, it is not a good idea to rely upon, as it removes water without removing the salt.

Number 2 complicates number 1. The Nile, Danube, Ebro and other rivers put their water into the Mediterranean, either directly or indirectly (Danube puts it's water into the Black Sea, which it turn flows into the Mediterranean). These rivers should be dammed as well, and the water used or diverted away, or the amount of water to be pumped away will increase.

The Nile can be dammed and diverted into Lake Chad to cover the entire Chad Basin. Desertic areas could improve on that. Also, some water could be allowed to flow north to irrigate the Sahara.

The Danube should be diverted into Volga to help the Caspian Sea avoid disappearing. Other rivers should be managed as well by similar means.

The important point with rivers is that city water usage creates black waters that should be disposed of. Without rivers moving those to the Mediterranean. For Rome, Barcelona, Cairo or the gigantic Istanbul, you'll certainly have sanitation problems. City usage by itself is not a method of removing water, as has been suggested in other answers.

Number 3 accounts for diminishing the amount of water available for creating clouds in southern Europe and northern Africa. As you pump water away, the climate will become drier, and cities and agriculture will suffer. The Sahara will grow North as the Mediterranean retires, eventually jumping it until maybe the line Pyrenees-Alps-Carpathians. This, in turn, may affect how you produce energy for the pumps of number 1. Nuclear energy needs a lot of water, either sea water of river water. If you are removing the Sea and the rivers stop flowing because there is no more rain, you can't use nuclear power. Neither can you use hydroelectric power, for the same reason: no sea→no rain→no rivers. You'll need to move energy from the Atlantic coast or from other sources (wind or sun).

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  • $\begingroup$ I don't object to your mentioning other subjects, I understand why it's relevant. +1. $\endgroup$ – Revetahw Sep 18 '16 at 22:45
  • $\begingroup$ "Black water", if handled properly by sewage treatment plants, does not exist. $\endgroup$ – Karl Sep 18 '16 at 22:55
  • $\begingroup$ Black water do exist and must be disposed of. Sewage plants is only one way of doing so (actually the best). Current tech level allows the water from such a plant to be reused only in small scales like the International Space Station, but not to establish closed circuit for water in cities, even less for industries. $\endgroup$ – Envite Sep 18 '16 at 23:02
  • $\begingroup$ Of course it is reusable, you can principally drink the water after any middle-european sewage plant. But it doesn't matter anyway, the mediterranean sea will completely evaporate in 100 years or so if you build that cruddy dam. Forget about rain and rivers. nat-meer.geomar.de/OzeanOnline/mittmeer/mittmeer.htm $\endgroup$ – Karl Sep 18 '16 at 23:16
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    $\begingroup$ The hydroelectric power from atlantic water is the only reason to ever think about building this thing, and it will all evaporate at the bottom. The flow rate of ten niles, and a height of 2000 meters or more. $\endgroup$ – Karl Sep 18 '16 at 23:53
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This answer works off the Mediteranean being 25000000000 cm cubed. If anyone knows a better figure please give it.

Natural evaporation - The Mediterranean currently loses 50-100cm cubed of freshwater per year. At this rate it will take over millions of years for the Mediterranean to evaporate. Probably too slow. This number may actually be too high as it does not take account of the fact the Mediterranean is salt water not freshwater and may also take account of rivers entering the Mediteranean but it will still be in the tens of thousands of years at the very least.

De-salination/water use - Use sea water as much as possible for coastal cities. Boil the water as it enters the city and then use it in your water grid. Sell the salt that is left for food and other things. 143 million people lived on the Mediteranean coastline in 2000 and that number is increasing. (Source: http://www.grida.no/graphicslib/detail/population-density-and-urban-centres-in-the-mediterranean-basin_1a99). The average person in the US uses 454609 cubic centimetres of water per day (http://water.usgs.gov/edu/qa-home-percapita.html). In total the Mediterranean coast uses around 60000000000000 cubic cm of water per day so the Mediterranean will be drained in less than a day. Of course the energy required is phenomenal but since resources aren't an issue this is probably the quickest way.

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  • $\begingroup$ I think when the mediterranean DID evaporate in the past it happened on the order of hundreds of thousands of years rather than tens of millions. I couldn't find a precise source for this, however. $\endgroup$ – A Simmons Sep 18 '16 at 21:09
  • $\begingroup$ @ASimmons You may be right, I was working off modern Mediterranean evaporation data and my rough maths which doesn't take account of the salt. $\endgroup$ – Bellerophon Sep 18 '16 at 21:11
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    $\begingroup$ There are 1000,000 cm3 in a m3 and a standard Olympic pool is 2,500 m3 so the figure quoted is 8 pools. $\endgroup$ – Donald Hobson Sep 18 '16 at 21:35
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    $\begingroup$ @bellerophon Your figures are WAY off $\endgroup$ – Donald Hobson Sep 18 '16 at 21:37
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    $\begingroup$ Add that your estimate for the volume of the mediterranean is by a factor of 150 millions off. en.wikipedia.org/wiki/Mediterranean_Sea $\endgroup$ – Karl Sep 18 '16 at 23:31

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