What is the largest possible artificial lake we could make today?

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bouer
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What is the largest possible artificial lake we could make today?

Postby bouer » Tue Aug 30, 2016 9:11 pm UTC

Humanity has made some impressive changes to the Earth's surface, but even our largest structures are dwarfed by small mountains, and our greatest mines are incomparable to some of the holes earth has made with erosion or tectonics.

Probably the closest we have come to nature in scale is with lakes. By area, the artificial lake Volta at 8500 km2 is the the 19th largest water body on the planet, 17th excluding the ocean and the Caspian sea. The artificial lake Kariba, 180 km3, is among the 30 most voluminous water bodies on Earth.

If we ignored the humanitarian and environmental damage, and wanted no better reason than 'because we can,' or 'https://what-if.xkcd.com/imgs/a/124/kennedy.png,' what is the largest water body we could make?

We'll take as much advantage of nature as possible, finding a preexisting basin, and letting rain and rivers fill it. We just need to make a dam.

The best contender I've seen so far is the Congo basin.
africaTopography.gif


A dam upriver of Brazzaville and Kinshasa, about 350 m tall, 1500 m wide at the river's surface, perhaps 10000 m at the top, and 1000 m thick at the base narrowing to 50 m at the top, seems to me to be enough to flood about half the Congo basin, 1 500 000 - 2 000 000 km2 to an average depth of 150-250 m.

The dam would be the largest ever constructed by volume, but not by height or length. It would be about the size of the next 15 largest dams combined, so might cost 10 times more than some of the largest, or about 100 Billion USD.

The reservoir would be the largest on the planet other than the ocean, 6 times greater in area than the Caspian, and 4 times greater in volume.

It would take at least a couple centuries to fill, possibly much longer depending on evaporation rates.

africa-physical-map-with-flooded-congo.jpg


Am I correct that this dam would be possible to construct with modern tools and technology?

Can you find any larger floodable basins, or other ways we might attempt to outdo nature?

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Re: What is the largest possible artificial lake we could make today?

Postby Zohar » Tue Aug 30, 2016 11:11 pm UTC

The straits of Gibraltar are only 15 km wide, and between 300-900 meters wide. It shouldn't be too difficult to close off the Mediterranean.
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Re: What is the largest possible artificial lake we could make today?

Postby Xanthir » Wed Aug 31, 2016 12:01 am UTC

As has happened in our relatively recent geologic past, and will happen again. It'll become an anti-lake, tho - gradually drying out and salinating as the water level drops due to evaporation.
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Re: What is the largest possible artificial lake we could make today?

Postby Soupspoon » Wed Aug 31, 2016 12:45 am UTC

Artificially melt a zone within the Antarctic continent, perhaps?

I've yet to review the geography in detail, but with meltwater being created within a still naturally subzero environment we have the ready means to solve most of the individual problems we also create (on the assumption that we are creating them with at least a modicum of awareness). Underlying topology aside, we would be melting the overlying topology and at the edge of our zone refreezing (either naturally or by megascale thermocouple cold-joints to our mid-lake hot-joints) the water trying to overflow our desired lake-side, forming additional shoreline elevation that (while we're already massively disrupting the planet!) we can accept as a dangerously unstable ice-dam that we'd necessarily have to consider the consequences of any breach thereof.

Any rocky mountaintops/ranges that the melting-and-levelling ice-mountain terrain exposes (but does not re-cover in melt-water held in by our ice-wall edges) we can just call 'islands' or peninsular incursions into the lacustrine zone. The big danger might be the relative delicacy of the necessary ice-dams made from both existing ice-sheet and our refrozen lake excess. Traditional glacial movement may be increased by the concentration of additional pressure (direct from 'splashed' icemountain summits) and increased lubrication (buoyant ice-walls would more readily accept seepage underneath, against the rock-bed, from the sulcus with the meltwater), and the movement would result in fissures probably requiring managed repair with the application of supercooled lake-water water to 'heal', if natural refreezing of leaks is not a quick enough process compared with the leaks melting the wall.

A delicate balance all-round, no doubt. Especially against the seasonal "freezing" (September-to-March-ish) and "bloody freezing" (April-September-ish) differences affecting the heat-differentials and absolutes a lot. Without continuous effort, extensive/total icing-over of the surface is inevitable, creating perhaps a Lake Giga-Vostok effect. Yet still with the potential of punching(/melting) through a side wall to violently drain out (and rip out more ice-wall that its energy doesn't directly melt), creating a now collapsing ice-roof over the void, leaving a drained horse-shoe 'crater' feature in its wake that would be an interesting featue to be discovered by whatever resurgent civilisation arose from the (damp) ashes of the resulting worldwide environmental chaos, or aliens, whichever first had opportunity to observe the remains of the project.

Yeah, I'm convinced. If we're going to mess the world up1, lets mess it up big. What we need now is a whole lot of heat-generators, perhaps some Peltier devices to define the edge of the zone (maybe half of which are driven by photovoltaic panels, usefully adding to the cooler edge when the sun is beaming down) and a whole-lotta black plastic (biodegradable?), black soot or similar to drape over/dope onto the interior to speed things up.

(And, in response to the more succinct ninja, at least my idea won't inevitably dry to salt, right?)

1 The beauty of my idea, compared with flooding the Congo/etc, is that I'm not creating too much difference in the overall geological stresses, if I'm using water that's already there and affecting tectonic stresses, except for possible minor localised rebound (from prior ice-mountain) and extra-pressure (prior ice-depresion). Putting maybe (if I haven't miscalculated) 225 teratonnes to half a petatonne of water over the Congo basin probably would cause stresses to the likes of the neighbouring Tanganyika fork of the Great Rift Valley. Which would be 'interesting' to behold.

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Re: What is the largest possible artificial lake we could make today?

Postby pogrmman » Wed Aug 31, 2016 3:08 am UTC

bouer wrote:
Spoiler:
Humanity has made some impressive changes to the Earth's surface, but even our largest structures are dwarfed by small mountains, and our greatest mines are incomparable to some of the holes earth has made with erosion or tectonics.

Probably the closest we have come to nature in scale is with lakes. By area, the artificial lake Volta at 8500 km2 is the the 19th largest water body on the planet, 17th excluding the ocean and the Caspian sea. The artificial lake Kariba, 180 km3, is among the 30 most voluminous water bodies on Earth.

If we ignored the humanitarian and environmental damage, and wanted no better reason than 'because we can,' or 'https://what-if.xkcd.com/imgs/a/124/kennedy.png,' what is the largest water body we could make?

We'll take as much advantage of nature as possible, finding a preexisting basin, and letting rain and rivers fill it. We just need to make a dam.

The best contender I've seen so far is the Congo basin.
africaTopography.gif

A dam upriver of Brazzaville and Kinshasa, about 350 m tall, 1500 m wide at the river's surface, perhaps 10000 m at the top, and 1000 m thick at the base narrowing to 50 m at the top, seems to me to be enough to flood about half the Congo basin, 1 500 000 - 2 000 000 km2 to an average depth of 150-250 m.

The dam would be the largest ever constructed by volume, but not by height or length. It would be about the size of the next 15 largest dams combined, so might cost 10 times more than some of the largest, or about 100 Billion USD.

The reservoir would be the largest on the planet other than the ocean, 6 times greater in area than the Caspian, and 4 times greater in volume.

It would take at least a couple centuries to fill, possibly much longer depending on evaporation rates.

africa-physical-map-with-flooded-congo.jpg

Am I correct that this dam would be possible to construct with modern tools and technology?

Can you find any larger floodable basins, or other ways we might attempt to outdo nature?


I don't think the catchment area could fill such a lake -- it seems like this lake fills too large a portion of the basin to fill. Just by guesstimating, it seems that the catchment area would be around 1.5 x of the lake -- which doesn't seem right.
Also, a body of water that big would probably have big effects on the weather and climate, not to mention the geological effects.

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Re: What is the largest possible artificial lake we could make today?

Postby bouer » Wed Aug 31, 2016 3:28 am UTC

I've found a few topographic maps that may come in handy. Warning, they are very large.

Africa (19 MB)
Spoiler:
largeafricatopographic.jpg


World (39 MB)
Spoiler:
Relief_World_Map_by_maps-for-free.jpg


Zohar wrote:The straits of Gibraltar are only 15 km wide, and between 300-900 meters wide. It shouldn't be too difficult to close off the Mediterranean.


Evaporation is one of the challenges we have. Damming the Med won't do much good, and neither will daming the far east of the Niger basin fill the Chad basin to it's maximum height.

Also, "shouldn't be too difficult" may be optimistic. The amount of material needed to build a dam increases linearly with length, but quadratically with height. It would be possible though.

Soupspoon wrote:Artificially melt a zone within the Antarctic continent, perhaps?


That's an interesting idea, although it almost seems like cheating, because the water was already there.

Image

Looks like you could make a hole a million kms2 in area and over a km deep, with at least temporary stability, but you'd need well over 3x1033 23 joules to melt all that ice. (106 kms3 of ice, 1025 15 cms3 to the km3, 1031 21 cms3 of ice, 306 joules to melt each cm3, >3x1033 23 joules, add inefficiencies)

We use around 1022 21 joules per year. Nukes release mere 1015 13-18s of joules.

Once we've successfully made this lake it'll be very temporary. Water is denser than ice, our lake is going to try to escape from underneath its walls.

1 The beauty of my idea, compared with flooding the Congo/etc, is that I'm not creating too much difference in the overall geological stresses, if I'm using water that's already there and affecting tectonic stresses, except for possible minor localised rebound (from prior ice-mountain) and extra-pressure (prior ice-depresion). Putting maybe (if I haven't miscalculated) 225 teratonnes to half a petatonne of water over the Congo basin probably would cause stresses to the likes of the neighbouring Tanganyika fork of the Great Rift Valley. Which would be 'interesting' to behold.


Zipingpu Dam added about a gigaton of water to its surroundings. That caused a 7.9 magnitude earthquake. A flooded Congo would add hundreds of thousands times more mass over tens of thousands times a greater area, albeit over tens of times as many years. If we spite mother earth by building a larger lake than any she's made, she might just make a larger earthquake than any in recorded history.

Edit: fixed a bunch of numbers, we could melt enough ice to make the largest lake on the planet, by increasing our annual energy production 10 times over and using most of it to melt ice for a couple decades, or with many thousands or millions of nuclear bombs.
Last edited by bouer on Wed Aug 31, 2016 4:15 pm UTC, edited 1 time in total.

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Re: What is the largest possible artificial lake we could make today?

Postby ijuin » Wed Aug 31, 2016 4:49 am UTC

I think you misplaced a decimal point there--it's 10^15 cm^3 in one km^3, not 10^25.

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Re: What is the largest possible artificial lake we could make today?

Postby Soupspoon » Wed Aug 31, 2016 6:24 am UTC

bouer wrote:Once we've successfully made this lake it'll be very temporary. Water is denser than ice, our lake is going to try to escape from underneath its walls.
I was thinking (but forgot to mention) that there'd need to be a wall (not necessarily watertight, but solid nontheless) at least 100m high above an ice barrier's water level at a point where the adjacent water is 1km deep, to bedrock, to start to 'ground' the ice edging across the wdth of the wall.

But, even so, the exact design (or natural formation that it tends towards) of the sulcus probably could not stop the ~100Atmos water-pressure trickling under any opportunistic gap and causing problems, as I did hint at. (If water seeped under and past the 'pressure wall' it could uplift the ice beyond that. I have a feeling that if there's no immediate catastrophe from that and the seep freezes more than the lifted ice melts that it would result in a self-regulating thickening of the wall as it heads towards self-creating near 10% elevation for almost as far out in width as is required to fully seal the boundary.

IANACivilEngineer, though, and this is just from mental modelling. The more dynamic outward pressure requires balancing (and, ideally more!) by retaining much more 'spread' of untouched ice-sheet, and even then I suspect that glacial movement and berg-calving would be sped up sufficiently to cause concern and increased dangers to shipping. The lake (left to its own devices, and the 'static' devices installed upon the flowing boundaries, would push outwards and increase in size. Less prsssure as the quantity of water lowers, but with bergy-bits coming off the edges to reduce the resistive match. Perhaps a lower ice 'flange' could be ensured, to help grip the bedrock, but I don't think that'd be easy to control the profile at depth.

At the surface, machines (perhaps based upon floating vessels, moving around) can stop the edge-ice forming/melting unevenly, but I imagine we'd end up with an overhang, still, at the very least...

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Re: What is the largest possible artificial lake we could make today?

Postby LucasBrown » Wed Aug 31, 2016 11:00 am UTC

We can avoid the issues presented by dams by simply flooding a pre-existing endorheic basin. In fact, we've already done this by accidentally creating the Salton Sea. The Salton Sea is currently 73m below sea level; to raise it to 0m, we could just dig a canal from the ocean to the New River or Alamo River and let gravity do the rest.

We could use similar methods to flood the Qattara Depression (as is occasionally proposed with some seriousness) or to raise the elevation of the Caspain Sea from its present level of -28m. The Qattara Depression Project would be the easiest to accomplish due to its proximity to the ocean, while flooding the Caspian would draw in the largest volume of water. The Salton option provides a middle ground on both the effort and the effect.

Other sub-sea-level basin exist, but they're either already full (e.g. Mediterranean Sea), considerably smaller than these options (e.g. Lake Enriquillo), or too far inland (e.g. Turpan Depression).

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Re: What is the largest possible artificial lake we could make today?

Postby bouer » Wed Aug 31, 2016 4:06 pm UTC

ijuin wrote:I think you misplaced a decimal point there--it's 10^15 cm^3 in one km^3, not 10^25.


Thanks, although at just 10 orders of magnitude off I don't know why you even bothered pointing it out.

So melting a hole in Antarctica is 10 billion times easier than I though.

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Re: What is the largest possible artificial lake we could make today?

Postby Soupspoon » Wed Aug 31, 2016 4:20 pm UTC

bouer wrote:So melting a hole in Antarctica is 10 billion times easier than I though.


Exactly. So... Does that mean that you're in on this little project, then? (You might have to bring your own shovel. The budget's a bit tight.)

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Re: What is the largest possible artificial lake we could make today?

Postby Flumble » Wed Aug 31, 2016 5:01 pm UTC

bouer wrote:
ijuin wrote:I think you misplaced a decimal point there--it's 10^15 cm^3 in one km^3, not 10^25.


Thanks, although at just 10 orders of magnitude off I don't know why you even bothered pointing it out.

First of all you do it to be technically correct, and secondly it suddenly makes the idea feasible: it's only a few decades of worldwide energy consumption (or years if we ramp it up, which is what you do when you want to melt Antarctica).

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Re: What is the largest possible artificial lake we could make today?

Postby bouer » Wed Aug 31, 2016 5:26 pm UTC

Soupspoon wrote:
bouer wrote:So melting a hole in Antarctica is 10 billion times easier than I thought.


Exactly. So... Does that mean that you're in on this little project, then? (You might have to bring your own shovel. The budget's a bit tight.)


I'm not convinced it will stay in one peace for even a year.

The entire "shoreline" will have to be something like a cliff at least 10% higher than the water depth, and pretty much vertical. If the ice wall is too short it will float. The submerged parts of the wall will be supported by the water, but the dry top will be very unstable.

If this reservoir is even 100000 cubic kms, to make it comfortably larger than the Caspian, and we make it as deep as possible, then we won't have problems with the walls being too short and floating, they'll be over a km higher than the water's surface in places.

I'm reading http://gji.oxfordjournals.org/content/1 ... l.pdf+html to try to figure out how the ice will behave.

Apparently features on the surface of the ice sheet are rarely more than 1/20th the thickness of the ice. Our feature will be the full thickness.

The ice sheet usually slopes between 0 and 5 m per km. We'll need slopes much greater.

Floating Ice shelves are relatively stable at a thickness of 250 m, with about 25m sticking above the water. Our walls will need numbers 4 times those at least.

Most of the ice on Antarctica moves at at least a few metres per year, near the edges it can reach a km per year. Near our lake I'd expect speeds greater than that. A few kms per year is a mm every few seconds.

I think if we melted such a huge hole in the ice, to the bedrock, the surrounding ice would begin immediately collapsing inward. It would decrease in height and flow towards the lake at quite high speeds, by deforming and calving. Once it had deformed enough, in less than a month with speeds of a few metres per day and a margin of 100 metres, it would begin to float. The water would squeeze between the ice sheet and the bedrock, lubricating and speeding up the flow, and decreasing the height of the lake so further damaging the stability of the area.

Can you stop a trillion tons of ice from moving where it wants to?

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Re: What is the largest possible artificial lake we could make today?

Postby Soupspoon » Wed Aug 31, 2016 8:04 pm UTC

bouer wrote:Can you stop a trillion tons of ice from moving where it wants to?
That's why we'll need the shovel.

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Re: What is the largest possible artificial lake we could make today?

Postby Tub » Wed Aug 31, 2016 9:10 pm UTC

If all you have is a shovel, I'd like to point your attention to a much smaller project. It is certainly not as ambitious as your other ideas, but successful completion would likely improve confidence among investors, hopefully allowing you to take out a loan for a second shovel within a few years.
The future lake I'm talking about is of course the Netherlands. You just approach the dyke, dig a little, wait for water to do its thing, then shovel the soil back to turn this part of the ocean into a lake.

Oh, before I forget: unless you can acquire the necessary permits, you might want to bring some kind of repellent to stop the local populace from interfering.

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Re: What is the largest possible artificial lake we could make today?

Postby bouer » Thu Sep 01, 2016 1:17 am UTC

Tub wrote:If all you have is a shovel, I'd like to point your attention to a much smaller project. It is certainly not as ambitious as your other ideas, but successful completion would likely improve confidence among investors, hopefully allowing you to take out a loan for a second shovel within a few years.
The future lake I'm talking about is of course the Netherlands. You just approach the dyke, dig a little, wait for water to do its thing, then shovel the soil back to turn this part of the ocean into a lake.

Oh, before I forget: unless you can acquire the necessary permits, you might want to bring some kind of repellent to stop the local populace from interfering.


What repels the dutch? Belgians?

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Re: What is the largest possible artificial lake we could make today?

Postby stianhat » Thu Sep 01, 2016 11:32 am UTC

I think the easiest large scale change we could do would be to remove a lake, not create one.

If you fill gibraltar and suez, the mediterranean sea will dry out within a generation or so and create a MASSIVE salt pan between europe and africa, with a tiny lake fed by the large rivers of europe but due to warm weather continuously drying out. There will likely be seasonal size variations, growing in winter and spring, diminishing in summer and autumn.

This will be a very noticeable change as it will also most likely change weather patterns and dust generation. There will be famine, war and chaos.


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