# Damming the Strait of Gibraltar **URL:** \ **Category:** Factual Questions\ **Created:** [October 21, 2005, 5:14am UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221 "2005-10-21T05:14:23Z")\ **Posts on this page:** 19\ **Page:** 1
**Author:** ![five\_to\_one](https://avatars.discourse-cdn.com/v4/letter/f/c68b51/32.png) [@five\_to\_one](https://boards.straightdope.com/u/five_to_one)\ **Post date:** [October 21, 2005, 5:14am UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/1 "2005-10-21T05:14:23Z")
Political and economic complexities aside, would it be technologically feasible today to dam the Strait of Gibraltar? Does the Mediterranean Sea require the Atlantic to survive? What would happen to the ecosystem of the Mediterranean? ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [October 21, 2005, 7:18am UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/2 "2005-10-21T07:18:13Z")
There was a program on TV recently which mentioned this. It said that this has happenned many times before naturally, and will happen again as Africa moves northwards. The Med will rapidly dry up without water coming in from the Atlantic (1000 years IIRC). It occurs to me that we could deliberately dam the Med and use the inflow to create electricity. ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [October 21, 2005, 4:15pm UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/3 "2005-10-21T16:15:02Z")
Venice would no longer have to worry about being flooded, and a whole lot of former seabed would become usable dry land. I don’t think these things would offset all the bad things that would result. In fact, when the natural dam reinstates itself, as **Quartz** points out, the nations of the Med will probably blast it away. ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [October 21, 2005, 4:19pm UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/4 "2005-10-21T16:19:55Z")
::Nott shakes his fist and rails at the distant strait:: **Dam you, Gibraltar!** ---
**Author:** ![caveman](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/caveman/32/7242_2.png) [@caveman](https://boards.straightdope.com/u/caveman)\ **Post date:** [October 21, 2005, 5:51pm UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/5 "2005-10-21T17:51:06Z")
> [@Quartz](#): > > There was a program on TV recently which mentioned this. It said that this has happenned many times before naturally, and will happen again as Africa moves northwards. The Med will rapidly dry up without water coming in from the Atlantic (1000 years IIRC). > > It occurs to me that we could deliberately dam the Med and use the inflow to create electricity. Even without water coming from the Atlantic, the med would still receive drainage from northern Africa\* as well as southern Europe, not to mention whatever drains into the Black Sea, should the water levels stay high enough. It’ll be waaay smaller, though. \*Now that I think of it, the Nile would end up being even longer than it already is, and eventually carve a (much) deeper course back into Egypt. ---
**Author:** ![Ponder\_Stibbons](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ponder_stibbons/32/343_2.png) [@Ponder\_Stibbons](https://boards.straightdope.com/u/Ponder_Stibbons)\ **Post date:** [October 21, 2005, 6:23pm UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/6 "2005-10-21T18:23:35Z")
> [@AskNott](#): > > Venice would no longer have to worry about being flooded, and a whole lot of former seabed would become usable dry land. I don’t think these things would offset all the bad things that would result. But what if a dam was built strictly with the idea of keeping sea level where it is today, or perhaps just a few inches lower, in order to compensate for the rise of the Atlantic due to global warming? ---
**Author:** ![bibliophage](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bibliophage/32/7615_2.png) [@bibliophage](https://boards.straightdope.com/u/bibliophage)\ **Post date:** [October 21, 2005, 6:30pm UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/7 "2005-10-21T18:30:22Z")
Evaporation averages greater than precipitation in the Mediterranean Basin (including the Black Sea Basin and the parts of North Africa that drain toward the Med). But The Suez Canal is a sea-level canal without locks. The water level would not fall unless both the strait and the canal were blocked. ---
**Author:** ![Noone\_Special](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/noone_special/32/2863_2.png) [@Noone\_Special](https://boards.straightdope.com/u/Noone_Special)\ **Post date:** [October 21, 2005, 9:11pm UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/8 "2005-10-21T21:11:40Z")
> [@bibliophage](#): > > Evaporation averages greater than precipitation in the Mediterranean Basin (including the Black Sea Basin and the parts of North Africa that drain toward the Med). But The Suez Canal is a sea-level canal without locks. The water level would not fall unless both the strait and the canal were blocked. Suez could probably be blocked by a concentrated effort involving roughly 10 truck-loads of sand 😛 I like the idea of damming Gibraltar and creating a HUGE hydro-electic plant there. This could be built in such a way that the level of the Mediterranean would be lowered by, oh say 20-30 meters. This would keep several coastal/island cities safe (if possibly tourist-free… I’m looking at you, Venice), give the countries bordering the Med some sizable tracts of new land to work with, and effect the Mediterranean ecology fairly little as a result. ---
**Author:** ![Charlie\_Tan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/charlie_tan/32/12582_2.png) [@Charlie\_Tan](https://boards.straightdope.com/u/Charlie_Tan)\ **Post date:** [October 21, 2005, 11:09pm UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/9 "2005-10-21T23:09:46Z")
> [@five to one](#): > > …the ecosystem of the Mediterranean… They have one? Seriously, the Med is pretty dead as seas go. Now, apart from the hydro-electric sceme (which doesn’t seem very feasible), why would you want to do this? ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [October 21, 2005, 11:34pm UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/10 "2005-10-21T23:34:33Z")
> [@caveman](#): > > Even without water coming from the Atlantic, the med would still receive drainage from northern Africa\* as well as southern Europe, not to mention whatever drains into the Black Sea, should the water levels stay high enough. It’ll be waaay smaller, though. Not enough to offset the evaporation, apparently. The program said that the water from the Rhone would evaporate before it hit the bottom. > [@](#): > > \*Now that I think of it, the Nile would end up being even longer than it already is, and eventually carve a (much) deeper course back into Egypt. You can see this on topographical maps: the delta is clearly shown. The Nile doesn’t cut a deeper channel because it’s laden with silt. ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [October 21, 2005, 11:38pm UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/11 "2005-10-21T23:38:47Z")
> [@The Gaspode](#): > > Now, apart from the hydro-electric sceme (which doesn’t seem very feasible), Why doesn’t it seem feasible? The volume of water is so vast you only have to drop the level a few meters. And Gibraltar isn’t that far from Africa. ---
**Author:** ![Martha\_Medea](https://avatars.discourse-cdn.com/v4/letter/m/43a26b/32.png) [@Martha\_Medea](https://boards.straightdope.com/u/Martha_Medea)\ **Post date:** [October 21, 2005, 11:42pm UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/12 "2005-10-21T23:42:46Z")
Not to mention the benefits of creating a handy land-bridge for all those would-be immigrants from Africa. :rolleyes: ---
**Author:** ![five\_to\_one](https://avatars.discourse-cdn.com/v4/letter/f/c68b51/32.png) [@five\_to\_one](https://boards.straightdope.com/u/five_to_one)\ **Post date:** [October 22, 2005, 4:53am UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/13 "2005-10-22T04:53:49Z")
> [@The Gaspode](#): > > They have one? > Seriously, the Med is pretty dead as seas go. Well, seeing how the area has supported a notable chunk of humanity for several millenia, that would suggest that there’s a fairly rich ecosystem inherent in the Mediterranean area. I would have to disagree on that point. Now, apart from the hydro-electric sceme (which doesn’t seem very feasible), why would you want to do this? [/QUOTE] I don’t know, maybe I’m a raging control freak. Or maybe I find thought experiments pretty constructive. The main point of my question was the feasibility of the idea, and if we have the technology to do something on that scale right now. Do you have anything constructive to offer? ---
**Author:** ![TheLoadedDog](https://avatars.discourse-cdn.com/v4/letter/t/35a633/32.png) [@TheLoadedDog](https://boards.straightdope.com/u/TheLoadedDog)\ **Post date:** [October 22, 2005, 5:00am UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/14 "2005-10-22T05:00:37Z")
You wouldn’t even need to dam the thing for hydro, would you? There are already powerful currents flowing in and out throught the Strait, one above the other. It might just be a matter of submerging turbines there. ---
**Author:** ![Fear\_Itself](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fear_itself/32/19637_2.png) [@Fear\_Itself](https://boards.straightdope.com/u/Fear_Itself)\ **Post date:** [October 22, 2005, 10:44am UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/15 "2005-10-22T10:44:02Z")
> [@Quartz](#): > > You can see this on topographical maps: the delta is clearly shown. The Nile doesn’t cut a deeper channel because it’s laden with silt. Not today; but 5.9 million years ago, when the Med dried up,[the Nile cut tremendous chasms as far back as Aswan](http://en.wikipedia.org/wiki/Messinian_Salinity_Crisis): > [@](#): > > Other evidence of drying comes from the remains of many (now submerged) canyons that were cut into the sides of the dry Mediterranean basin by rivers flowing down to the burning hot dry desert of the abyssal plain. For example, the Nile cut its bed down to several hundred feet below sea level at Aswan and 8000 feet (2,400 m) below sea level under Cairo. ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [October 22, 2005, 5:00pm UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/16 "2005-10-22T17:00:13Z")
> [@Ponder Stibbons](#): > > But what if a dam was built strictly with the idea of keeping sea level where it is today, or perhaps just a few inches lower, in order to compensate for the rise of the Atlantic due to global warming? The ships have to get in and out somehow. Count the port cities in the Med, and you’ll get an idea how many rich, powerful shippers you’d piss off. ---
**Author:** ![Noone\_Special](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/noone_special/32/2863_2.png) [@Noone\_Special](https://boards.straightdope.com/u/Noone_Special)\ **Post date:** [October 22, 2005, 5:02pm UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/17 "2005-10-22T17:02:31Z")
> [@AskNott](#): > > The ships have to get in and out somehow. Count the port cities in the Med, and you’ll get an idea how many rich, powerful shippers you’d piss off. As long as the difference in levels isn’t too great, this can be dealt with by using a lock system, like on overland canals (think Panama), off on one side. ---
**Author:** ![wolfstu](https://avatars.discourse-cdn.com/v4/letter/w/d6d6ee/32.png) [@wolfstu](https://boards.straightdope.com/u/wolfstu)\ **Post date:** [October 23, 2005, 3:12am UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/18 "2005-10-23T03:12:13Z")
Saith [Wikipedia](http://en.wikipedia.org/wiki/Strait_of_Gibraltar): > [@](#): > > The depth is about 300 m, and it is about 14 km wide at its narrowest point. Constructing a dam would presumably involve dumping enough rock and fill into the strait to fill up that 300 metre depth, and thick enough to hold back the pressure of that much water (which works out to about 3000000 MPa, or ~30 atmospheres, in my quick mental calculation). I’m not sure how thick a dam needs to be to hold that kind of pressure, but at that depth and a 14-km width, it’s going to be a /lot/ of material. Also, the undersea currents are apparently so strong that submarines (at least those of the WWII era) can’t cruise against them, and have to travel on the surface if they’re planning to run the straight from the Mediterranean to the Atlantic side. So if we just sail boats out into mid-strait and push dirt overboard, it’ll get spread all over by the currents, making the process tremendously inefficient, if not hopeless. Often damming a river involves diverting it first so you can prepare the foundation of the dam; I don’t think this is practical with the strait. Also, you’d be installing all the turbines and machinery below the current waterline. That’s not how river dams are usually built, and there’d be some technical challenges there. ---
**Author:** ![matt\_mcl](https://avatars.discourse-cdn.com/v4/letter/m/7ab992/32.png) [@matt\_mcl](https://boards.straightdope.com/u/matt_mcl)\ **Post date:** [October 23, 2005, 5:09am UTC](https://boards.straightdope.com/t/damming-the-strait-of-gibraltar/327221/19 "2005-10-23T05:09:32Z")
Many people here are bandying the name “Gibraltar” about. I would like to clarify that although they are the Straits of Gibraltar, contrary to popular belief, the peninsula of Gibraltar is not actually the chokepoint of the strait. The peninsula immediately to the west of Gibraltar, on which the town of Tarifa is situated, protrudes some distance south of Gibraltar.