Flooding the Sahara

Discussion in 'Alternate History Discussion: Before 1900' started by Dr Pervez Hoodbhoy, Dec 3, 2005.

  1. Iori ダークアビスの特使。

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    We're talking about the middle of the desert here, yeah their are some things living their, but it would'nt be a disaster unless you literally flooded the entirety of the Sahara (and thus most of the Northern 1/2 of Africa).
     
  2. DuQuense Commisioned Officer CSN

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    Thing is along the Med coast is a range of hills. The Coast side has a very shallow slope. So shallow that 18th century European Explorers didn't realize how far they went up.
    On the south side of the hills the slope was a lot steeper.
    As such most European Explorers came away with the illusion of the Sahara as a great below sea level bowl.
     
  3. karl2025 Well-Known Member

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    Oct 1, 2007
    It's not a closed system. Altering the environment of the desert will alter the environment elsewhere as well. Higher humidity from increased evaporation in the area leads to fewer particulates being picked up from the desert, particulates that are rich in nutriants and help fertilize other areas of the world as far away as Brazil, the SE USA, and Caribbean, not to mention more local areas and the seas. The dust is also a regulator for rainfall, again, across a wide area. There's also the question of where the water would come from and what that'd mean for said region.
     
  4. General_Finley Liberty Prime

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    I'm thinking of including the flooding of the Qattara Depression in my TL "The Federal Republic of America" as one of the Mega projects the French and British Empires do to try and one up each other. It'll lead to the extinction of the Cheetah, the Fennec Fox and several other animalsnative to the region.
     
  5. jackalope To Serve Man -- Twilight Zone

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    Note the recent Eyre basin posts. Flooding the Quatara basin is not so great, probably. Most of the evaporated water would never rain nearby.
    It is best for evaporation proceedures of salts, but since there is a
    500 foot head to pump over and a 40 mile? or so length from the
    Mediterranean, the one in Tunisia/Algeria is far better. Besides, the
    locals do not like to mess with mother nature, sort of a mother earth &
    Muslim thing.

    Salt is mighty cheap nowadays. Too many places it is being harvested
    or mined. Not at all like the old days.

    RE the raining proposal, it does seem there is some truth in the macro
    side, as when there were lakes in the Sahara, til about 3,000/4,000
    BC, it did help, partly probably as allowing the atmospheric high to
    break occasionally and have more storm tracks probe the expanse
    during winter. But part of that was the residual cold of the north,
    and the ground is still like that in thermocline in many places of the
    earth. Tidbits of icesheet still were in the baltic til 7,000 years,
    for example.

    The lakes in the Sahara were huge, but certainly oscillated up and
    down regularly. Evaporation is usually about 4 feet in such places,
    but better ground cover, lower albedo, etc would help. Quattara is a
    flea puddle by comparison of what was, so do not expect a big difference
    except to some roving Camel Bedouins, which rode hundreds of miles for
    a rare gulley washer, not enough for a civilization to flourish.

    Flood the Tunisian one instead. Much more practical and easier than
    building the Suez canal by far. Not so the Quatara.

    But write whatever you want.
     
  6. General_Finley Liberty Prime

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    Sep 2, 2009
    You instantly changed my mind. What was the name of the Tunisian one?
     
  7. Barry Bull Donor

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    Exactly! Ecological consequences of human engineering is much more than the effects to wildlife in the proejct site. I sometimes too many people misunderstand the term "ecosystem" in a purely biological way.
     
  8. jackalope To Serve Man -- Twilight Zone

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    Instantly? Uh oh.

    Anyway, this thread was started by the Tunisian/Algerian Gulf of Triton/
    Chott el Hodna issue. The maximum depth is about 45 feet, but it is
    very large. Unfortunately a great big date oaisis needs to be flooded,
    and the water would be difficult to transport to another location,
    thousands live in the area, according to the links posted by others here.

    http://en.wikipedia.org/wiki/File:Algeria_Topography.png
    The very darkest green areas are the parts referred to.


    http://en.wikipedia.org/wiki/Chott_el_Djerid

    http://en.wikipedia.org/wiki/Chott_Melrhir

    From the links on this thread posted by others, it seems that about
    300 AD to 800 AD the passage became closed by drifting sand and now
    is very closed. After the enormous political ramifications and
    fence mending, then open a small channel, hire people to load up
    shallow 3 foot draft barges full of material dredged from bottom,
    and let the thing grow naturally. The head is only about 40 feet over
    100 miles plus. Have it wind in circles to drop various salts out
    in precipitation, plus the algae content. Without the algae producing
    oil (as yet unrealized in commercially viable ways), this would not
    be very useful as a project.

    Avoid the oasises, easily done since the levees need only be a foot or
    two high. Seepage would slowly raise and extend this, especially in the
    critical low areas were the oasis date farms are. Eventually the area of
    the lower areas would get clogged (inch of salt a year), raising towering
    levees of waste (Non NaCl) salts thick and strong. Sounds exotic, but
    the best I can do off hand.

    And if for some reason the levees burst? Not much behind them except
    precipitated salt and a foot or so of very salty water. However, a danger.


    http://books.google.com/books?id=dm...EwAA#v=onepage&q=lake pallas, tunisia&f=false



    http://en.wikipedia.org/wiki/Gulf_of_Gabès
    Note that the intake area has up to 2.1 meter spring tides,
    positively huge for the Mediterranean area, normally tideless.

    This makes some interesting variations on engineering.

    Good Luck
     
  9. jackalope To Serve Man -- Twilight Zone

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    That should read "inch of salt per year" on average. Obviously,
    as any salt harvester would tell you, the bottom areas and
    other pinch points would get literally feet of accumulation a
    year and the intake points would get just a tiny amount of
    lime. Gypsum precipitates out inbetween I recall.
     
  10. Leistungsfähiger Amerikan Angry American with Guns

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    How much would these lakes aid in agricultural output of the region? It seems to me that just putting water in the Sahara isn't suddenly going to make it arable land.
     
  11. jackalope To Serve Man -- Twilight Zone

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    As said in posts about Lake Eyre (Australia) at this site (other
    forum before or after 1900, I forget), all deserts are poor places to
    expect rain, as air is decending, therefore starting out extremely
    dry, and prone not to ascend (thundercloud or weather
    front). This makes rain hard to come by. And the elevation
    depressions are too small here to have gravity feed inlets
    provide that much for water. But there would be some extra
    water at times. Changing climates by surface change is
    a well known issue, usually for the worse via human activity.
     
  12. Vitruvius Donor

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    Nov 20, 2008
    I'm also doubtful, for reasons that others have elaborated upon. Based on what I've read of the original French proposals, they relied upon mid 19th century understandings of weather and hydrology. It was assumed that putting a shallow sea in southern Tunisia and extending it into Algeria would moderate the climate of northern Tunisia and coastal/mountainous regions of Algeria. Moderate perhaps in terms of temperature but I'm not sure it would actually increase precipitation, but then I'm no expert.

    Another point the French made was that such a sea would help them dominate the caravan trade across the Sahara. At the time most routes went to Morocco or to the Med in Tripolitania, both outside French control. But a new sea extending into north-central Algeria would be an obvious new terminus for such trade allowing the French to control it.

    Even at the time there were concerns, namely that the only oases in the area would be flooded by a salt water sea. Thus to replace that lost production the sea would have to generate more rainfall and not everyone was convinced it would. The project would also require continuous dredging to keep the channel open to the Med and thus keep the sea from drying up again.

    The whole Lake Triton project was driven by 19th century science, economics, geo-politics and understandings of what modern societies were capable of achieving. Many of the tenets underpinning the project may not have been born out had it gone forward. Not to say that it couldn't have been done, just that once completed it might have proven to have been a colossal boondoggle.
     
  13. jackalope To Serve Man -- Twilight Zone

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    The project would also require continuous dredging to keep the channel open to the Med and thus keep the sea from drying up again.
    ---------------------------

    Vitruvius, the dredging would be miminal once in place. Currents on
    the coast are small, and wind blown sand could be stablized. Over
    centuries with little commercial use, or at least during periodic times
    of turmoil, were the reason for silting up. The canal from the Nile
    to the Red Sea had the same happen, with far more traffic and need.
    It happened over many centuries, though.

    The gradient is a mere 4" per mile, or 40 feet per 160 miles or so, with
    an initial depression at 80 miles of up to 30 feet. This is fairly small
    but not insignificant, so spoil banks of hydraulically sluiced sand, silt
    and mud might be best. But during the 1900s this is folly indeed.
    Suez was a success, but Panama was not for the French. Hydraulic
    sluicing was really a California Gold Rush mining technique only later
    adapted for cheaper removal (about 1/3 as expensive, I recall). Run
    off would be miminal with normal years in the dry climate.

    Most of the region is flat, and heights are a maximum of 10 feet above
    sea level or so, and only a few of those.
     
  14. Vitruvius Donor

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    Nov 20, 2008
    Fair enough, I will defer to you on this. Engineering projects of this nature are straying outside my area of expertise. I was merely relaying the contemporary critiques that I've read.

    I guess the question I was getting at is what the project is supposed to accomplish vs what it can accomplish. From what I've read the French had two aims, improving agriculture to the north through climate modification and improving commerce to the south by opening up access to the interior via the new sea. I see the second as doable, except the shallow nature of the sea will limit access to Ocean going vessels (unless the channel is deepened but that brings up dredging again). But I think no one has yet determined whether it can truly be beneficial to the microclimate of Northern Algeria/Tunisia. So for ATL purposes it seems like guess work/it does what ever you want it to do for the purposes of a particular TL.
     
  15. DuQuense Commisioned Officer CSN

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    There is a 3rd Major Depression in Libya, which I [Great Isreal TL] have the Italians of the 20's flooding for Power Generation. [Bauxite]
     
  16. General_Finley Liberty Prime

    Joined:
    Sep 2, 2009
    I'd like to include a flooded Chott el Djerid in my TL.

    If possible could someone edit the below map to include it if possible?

    Enhanced%20Blank%20Map%20v2.png
     
  17. Vitruvius Donor

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    Nov 20, 2008
    Ok well I think we need to clear some things up. The original French proposal was to flood the Chott Al Djerid. But you can't because its above Sea Level. As DuQuesne pointed out Europeans overestimated the depressions in southern Tunisia, they thought Djerid was 60' below but its actually above.

    So once surveys were done they modified their proposal. Basically they would dig a canal all the way to Chott el Gharsah(Rhassah). This and the larger and lower Chott Melrhir are definitely below sea level and floodable. So the final French proposal was what you see here.

    [​IMG][​IMG]

    So on a modified world map the sea looks pretty insignificant and hard to read.

    [​IMG]

    To get a better idea I've cropped it to just northern Algeria and Tunisia.

    [​IMG]

    For clarification the first image is pulled from this rather detailed article on the French proposal as amended after the geological surveys conducted after it was first proposed.
    [​IMG]
     
  18. Valdemar II Banned

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    Interesting, personal I think they should focus on filling Chott Al Djerid, it's not much above sea level, and as such a few hundred windmill can slowly pump sea water into it, in the east a canal can lead the brine to Chott Melrhir, Chott el Gharsah could be kept empty except for a canal to Melrhir, the increased humidity would transform Gharsah into an fresh water lake, while Djerid would be a saline lake and Melrhir a western version of the Dead Sea.

    Gharsah could be used to irrigate the area around the lake.
     
  19. jackalope To Serve Man -- Twilight Zone

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    Uh, Chott Al Djerid is at least 30 feet (10 meters) above sealevel, more
    than is normally uplifted in the harvesting of salt. Plus a 30 mile canal
    from the Mediterranean, minimum. And humidity would be mostly
    unchanged, as the Sahara is decending air (extemely dry) and that air
    leaves often in hours to hundreds of miles away, just like most deserts.
    Chott el Gharsah is only about 15 miles long by 3 miles wide, and no
    one lives or grows crops there. Curious why it would be important to
    leave isolated. The town is well above sea level about 50 feet or more.

    This thread has been dead for well over a year, but I posted some
    rather questionable matters on elevation. The hump shown in the
    1800's French map above does not show, but with the new url
    topomapper lists it. The top is about 3 miles of 150 feet (about
    50 meters). Only 18 feet and the water starts to cavitate? So
    siphons will not work. This means a cut.

    The Chott Al Djerid will very possibly be easy to dig, as it is salt.
    Disolve it away. But for 30 miles (50 Km) at very least a loose
    alluvium must be piled up to make a canal. Salt pans are normally
    very simple 5 feet hydraulically sluiced dredgings, and salt now
    is sold for very little money, especially raw salt.

    Plus the Tunisians and Algerians are wary of the plan. Looks like
    the Roman and other texts are incorrect that the inland lake was
    connected to the sea in those days. 30 miles of an average 90
    feet is a lot of earthquake uplift in 2,000 years for that region
    (but not for Chile, as some mega tremors have done about that
    in one shot), and drainage inward would seem unlikely to be
    so much over such a wide expanse.

    If anyone is serious about these plans, now you know.
     
  20. nimbletoes Well-Known Member

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    Nov 9, 2009
    I daresay they could keep the Qattara depression flooded, monkey; the evaporation itself would keep the area flooded, because with water being drawn off all the time by being lost to the sun's heat, there would be a constant inflow of new sea-water to the inland sea. All you have to do is ensure that the water can flow in constantly without being lost to evaporation on the journey across the desert (ca. 80 miles, IIRR) from the Med. coast to the northern rim of the Qattara Depression.) This could be done easily enough by cut-and-cover, ie cut the canal and cover it with a ground-level roof to keep the sun off.:)