Offsetting sea level rise: An engineering idea of Biblical proportions

September 18, 2009 4:52 AM

The seas are rising. Climate change has made it inevitable. I have a strange question... Assuming that world sea-level rises by 1 metre over the next hundred years - Would it be possible to cordon off a section of land, somewhere in the centre of a continent, and flood it to create an artificial ocean, thus reducing the consequences of the sea rise?

This Biblical scale engineering feat must take these issues into account:

1. The section of land would have to be a very large 'bowl', in the centre of a continent, that is already below sea level. Another section of land, leading from the ocean to this central 'bowl' section, would have to be carved out to create the biggest dam system mankind has ever witnessed. Does somewhere like this exist?

2. The number of humans currently living in this 'bowl' would have to be less than the number of humans who would be displaced by the 1 metre sea level rise. Otherwise this huge engineering feat would not be worth undertaking.

3. Other environmental issues should be taken into account, such as the ecosystems that would be displaced or the new weather patterns and ocean currents that would be created.

Do you have the calculations of water/land displaced? Or ideas about where this kind of thing could be built? I'd love any input on this monstrous thought experiment.

Thanks!

posted by 0bvious to Science & Nature (30 answers total)

Best answer: Looking at wikipedia, the oceans have a surface area of 360,000,000 square km. Ignoring the changing coastline, a 1m rise means an approximate additional volume of 3.61 x 10^14 m3, but it's likely to be much more.

Again from wikipedia, the Dead Sea is the lowest area below sea level. It's got a surface area of 810 km2 and is 418 m below sea level. Assuming you could flood all that additional elevation and that the increase in surface area due to sloping sides allows for, I don't know, a four-fold multiplication of the available volume, that gives you an available volume of 1.35 x 10^12 m3.

So if all of that held approximately true, you're looking at least at something like of the order of 100 dead seas to hold it all.

Perhaps the hive can do a better job than me, but there's something done in a hurry to kick things off...

I'd love to be the one that's allowed to open the floodgates. I bet someone would want to ride the wave.
posted by dowcrag at 5:08 AM on September 18, 2009 [2 favorites]

List of places on land with elevations below sea level
posted by jwells at 5:18 AM on September 18, 2009

The first place that comes to mind is the Dead Sea. That basin is the farthest below sea level and used to be part of a bay that would flood periodically until the land mass rose enough to cut it off from the Mediterranean, isolating it.

I'm not particularly confident it could hold enough water to make much of a difference in your scenario (certainly not 1m), but it could hold vastly more water than it does now, as shown historically. You could expand that idea out to include the surrounding Jordan Rift Valley I suppose. As for population displacement, that area is not heavily populated as far as I know.

Possible repercussions of this kind of experiment: flood the valley, western hills erode and oops, there goes Israel. So there might be a little push-back on that front.
posted by empyrean at 5:21 AM on September 18, 2009

Best answer: Taking the above figure of 360 million km^2 of ocean surface area...

For an artificial ocean of 1 m deep, it would be 360,000,000 km^2 in surface area.
For an artificial ocean of 500 m deep, it would be 720,000 km^2 in surface area (slightly larger than Texas: 696,000 km^2).
For an artificial ocean of 1 km deep, it would be 360,000 km^2 in surface area.

Say we went with 1 km deep. If it was a circular lake, it would have a perimeter of 2,126 km.

If we say 1 km high by 2,126 km long, by.... 1 km thick? You're looking at 2,126 km^3 of concrete (or whatever material).

Current world annual production of concrete? 7.5 km^3. Of course you could always dig a 500m deep hole and half the wall material needed.
posted by EndsOfInvention at 5:32 AM on September 18, 2009

Instead of putting water on land, why not deepen the oceans (by an average of 1m) and dump the soil somewhere with lots of empty space instead? If we're talking about impossibly large-scale projects that alternative should be kept in mind, I think.
posted by bjrn at 5:40 AM on September 18, 2009

Response by poster: This project would involve very little concrete, apart from the dam perhaps. The entire bowl is below sea level, so building an artificial river from the sea to the bowl will drain the water off the sea. Deepening the oceans would require a lot of digging at an astronomical cost (underwater diggers?). Again, here are the main parts of the job:

1. Dig a massive dam/river system from ocean to below-sea-level-bowl-region.
2. Move people out of the bowl
3. Open the flood gates

Some great maths going on here. Is the Dead Sea and surrounding area the only possible place? How much would it cost to do this?
posted by 0bvious at 5:51 AM on September 18, 2009

Best answer: I got surface area numbers for half the stuff* on that Wikipedia list, converted the elevation below sea level to km, multiplied, and then converted to cubic meters. It's roughly 4.89786208 × 10^13 cubic meters. That's a laughably ballpark figure that makes wild assumptions about depth (average is probably much less than the numbers on that list), etc.

* Dead Sea, Sea of Galilee, Turfan Depression, Lac Assal, Caspian Depression, Qattara Depression, Tiberias, Bet She'an, Furnace Creek Airport, Salton Sea, Lago Enriquillo, Chott Melrhir, Caspian Sea and its shores, Lake Eyre, Hachirogata, The Fens, Canvey Island, Kristianstad, New Orleans, Kuttanad, Rhone River delta, Żuławy Wiślane, Lagos Island.
posted by jwells at 6:04 AM on September 18, 2009

Response by poster: jwells: most of those below sea level figures are 'bowl' types, but some are merely low lying coastal regions. The Lagos Island is just an island. It could not be used to store the offset. But anyway. Assuming that 4.89786208 × 10^13 cubic meters is the most that we could squeeze from the land, across the world, would it be enough for a 1 metre sea rise?
posted by 0bvious at 6:20 AM on September 18, 2009

Of course, a massive inland sea is going to have climate repurcussions as well...
posted by DU at 6:25 AM on September 18, 2009

Six of one, half a dozen of the other. You're proposing that we give up a huge area of land to create an ocean to keep us from losing huge areas of land from the encroaching ocean.
posted by Liver at 6:35 AM on September 18, 2009 [3 favorites]

The easiest way would probably be to find an existing large natural lake, and dam it so that the water level rises. Lakes do tend to have cities on them, but that's life.
posted by smackfu at 6:36 AM on September 18, 2009

I agree - I was just trying to get a ball park figure to see if it's worth a more serious look. It's still an order of magnitude off of dowcrag's rough estimate of the volume needed, but I didn't get everything and with the average/maximum depth and coastline issues there's enough uncertainty that it might be worth a look by someone with modeling software. At the very least it could put a dent in the issue (1/100th).

Try challenging the folks in the WorldWind forums to see if they can do it. If they can they might be able to look at population maps to see which ones are least populated, etc.
posted by jwells at 6:52 AM on September 18, 2009

well there is not a lot of wildlife / people or arible land in in parts of central Australia. But you'd have to dig it down a bit to hold much water.
posted by mary8nne at 7:04 AM on September 18, 2009

It seems like this would be an exercise in utter futility when you look at the surface area of the oceans vs. the available surface area of land available to take said ocean water. I don't think you could viably affect ocean levels by more than an inch or two, and you'd just offset the environmental disaster to another place.

That said, the Aral sea could really use an influx of water right now. getting it there from the nearest ocean however, is problematic.
posted by Devils Rancher at 7:09 AM on September 18, 2009

Six of one, half a dozen of the other. You're proposing that we give up a huge area of land to create an ocean to keep us from losing huge areas of land from the encroaching ocean.

Which is exactly why we should just dig a trench/river through California and let ocean spill into the San Andreas Fault instead.
posted by mikepop at 7:11 AM on September 18, 2009

just a couple of links to add in, seems like nature might be having the same idea...

The Arbonian Sea from 2005
Return to Arbonia from 2006
both posts from one of my faves, bldgblog.
posted by Bohemia Mountain at 7:32 AM on September 18, 2009

Since we're playing Crazy Corps of Engineers, why not dig a giant mohole deep into the planetary crust? A narrow deep hole takes a lot less real estate than a wide shallow one.

-
posted by General Tonic at 7:35 AM on September 18, 2009

I doubt very much this one idea would address the issue, but I do think it'd have an effect and could be part of a larger plan, which is why I'm saying it's worth modeling. Tuvalu's highest part is 4.5m above sea level. Centimeters matter to folks in their position.

There are upsides to it as well. Coastal lands globally are over crowded and this could create more. We'd have a better buffer if we ever needed it. If you can close and open the gates then that's a good salt pond - slap a clear dome over a small portion and you can harvest the desalinated water that condenses on the dome, or forget the dome and wait for evaporation to create massive salt flats.

Mostly though I just know water always finds a way to the lowest point, and letting it do that on it's own seems very reckless to me. It's not like we've never done anything this big before. The Panama Canal was dug in the early 1900s and the Suez has been done a few times, apparently.
posted by jwells at 7:52 AM on September 18, 2009

Response by poster: What better way to calm the problems in Israel than to flood the entire region?

But seriously, I too think it's an idea we should consider - or I wouldn't have asked the question. Coastal regions around the world are the most densely populated, even if you take out of the figures places like New York, London and Tokyo which are all mainly just above sea level. The other option of course would be to put a vast sunscreen into orbit above the Arctic and/or Antarctic, effectively cooling those regions down. That might reverse some of the damage we have already done and re-lock a lot of that sea-water back into ice.

mikepop: Flooding the San Andreas fault - that is the most genius - and probably most reckless thing - I have heard in a while.
posted by 0bvious at 8:08 AM on September 18, 2009

Best answer: Humanity lacks the manpower and resourses to construct such a hole.

If all people would start moving rock right now, then we would have 10 billion people working 100 years. That's 1e12 man-years worth of sweat. (a one followed by 12 zeroes)
Each individual would have to move 500m3 of rock (that is 1200000kg) a year, or 3300kg daily, over a distance of at least 28km (the radius of a half-sphere with a volume of 4.8e13m3).

We might as well make a drain hole in the ocean...
posted by Psychnic at 9:11 AM on September 18, 2009

How much water could the Aral Sea take? And what would be involved in piping seawater to it?
posted by musofire at 9:16 AM on September 18, 2009

How much water could the Aral Sea take?

According to Wikipedia, its volume in 1960 was 1100 cubic kilometers, and by 1998, it had lost 80% of its volume. Doesn't seem to give a more recent estimate.

But let's say its volume is currently zero. Then getting the world's largest bucket brigade to dump water from the world ocean into the Aral Sea, until it got back up to its 1960 volume again, would reduce the volume of the world ocean by less than one-ten thousandth of one percent.

This would be enough to offset something like three millimeters of ocean level rise.
posted by Flunkie at 10:24 AM on September 18, 2009

Just throwing this out there, but you don't really need to use places that are below sea level. You really just need a place that has sides that are higher then the middle. Lake Superior is 600 ft above sea level and that holds a pretty decent amount of water. Based on the calculations above, it's still about 30 times less then you would need to contain a 1m rise in sea level, but it's a start.

From an environmental standpoint the problem is that the water is salt water, so putting it anywhere that would normally see fresh water can have some pretty terrible effects.

As an aside, underwater digging is pretty commonplace.
posted by jefeweiss at 10:25 AM on September 18, 2009

Humanity lacks the manpower and resourses to construct such a hole.

Why are you doing this the hard way? We can just divert an small asteroid to carve out a crater. Bonus - debris from the collision fills the atmosphere creating a temporary cooling effect, perhaps mitigating the sea rise to .8 meters.
posted by mikepop at 10:34 AM on September 18, 2009

mikepop: "Humanity lacks the manpower and resourses to construct such a hole.

Why are you doing this the hard way? We can just divert an small asteroid to carve out a crater. Bonus - debris from the collision fills the atmosphere creating a temporary cooling effect, perhaps mitigating the sea rise to .8 meters."

Or you can just nuke the hole, that should have about the same effect.
posted by jefeweiss at 10:46 AM on September 18, 2009

Of course, a massive inland sea is going to have climate repurcussions as well...

I'll volunteer the Nullarbor. Used to be a sea.
posted by pompomtom at 5:04 PM on September 18, 2009

Heck, put the water in the Great Basin! We'll lose Salt Lake City and Reno, but I'm actually OK with that.
posted by gum at 5:13 PM on September 18, 2009

Best answer:

Heck, put the water in the Great Basin!

If we're going to go that route, the Great Basin is just a bit player. Here's a map of the world, with endorheic basins shown in grey (and the lakes they drain to in black).

I imagine a whole lotta water can, theoretically, be stored in central Asia. I imagine that this would have a significantly negative effect on our relations with, Iran, China, and Russia, amongst others, and so am surprised that this has not yet been proposed as a solution to global warming by any Republican member of Congress.
posted by Flunkie at 6:07 PM on September 18, 2009 [1 favorite]

The Qattara Depression is probably do-able, it's not too far from the sea, and there's very little of anything there to be flooded. I recall a few years ago reading about a proposal to generate hydro power by draining sea water into the Qattara - it's so hot there the inflow would be many times the volume of the depression due to the high evaporation rate. This, of course doesn't address your problem, and filling the Qattara completely isn't going to make a big dent in sea levels.
posted by HiroProtagonist at 7:29 PM on September 20, 2009

Some interesting reading on previous plans to engineer oceans - Atlantropa.
posted by nfg at 8:55 AM on September 24, 2009