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# Idea: Greening the Sahara with cheap undersea freshwater transport

Here's an idea I posted back in 2010 on SF writer Charlie Stross' blog:

[Cut interesting stuff about mass desalination, uses for brine in solar-thermal storage, direct wind-electricity conversion, increasing evaporation and rainfall with passive boundary layer disruptors.]

Which brings up another thought - the outflow of the major rivers into the Mediterranean and east Atlantic is mostly wasted. Perhaps the smart solution to greening the Sahara is just to build bloody big pipes to move the fresh water. Neutral to slightly positive buoyancy, guyed to the seafloor, deep enough to be mostly out of harms way but shallow enough for divers to repair. The sea salinity would be preserved by leaving most of the rivers' waters to go out to sea, and by the fact that the water will only be temporarily held by the new Saharan ecosystem, in the long run raining back into the sea (and providing more cloud cover on the southern Mediterranean shore which could make the waters cooler and thus more fertile.) A pressurized system would be desirable to move the water and keep the seawater out, so the pipes could be made from tensile materials, such as flexible plastics which would also prevent corrosion and allow integrated safe anti-fouling compounds (silver ions, not too expensive because of the low amounts needed). Using flexible sheet materials, and looking at the cube-square law for very big pipes (hoses, really), the mass of the system apart from the gravel in the anchors would be less than 1/10,000 the water in the system and on the order of 1/100,000,000 of the water delivered in a year. So even if a ton of water is worth a penny and a ton of hose costs $100,000, it would still have a gross payoff of 10:1 in a year, more than enough to pay for the rest of what would be needed. It's hard to find that kind of economy in a desalination scheme. ## Comments • Options 1. edited April 2016 How would these costs compare with solar desalination along the north african coast, especially with the new Moroccan and Egyptian mega sites? Comment Source:How would these costs compare with solar desalination along the north african coast, especially with the new Moroccan and Egyptian mega sites? • Options 2. edited April 2016 There are a lot of variables, maintenance in particular, but solar desalination is likely 10 to 100 times more expensive than piping rivers. Searching on "solar desalination cost" gives a figure of$1.52 - 2.05 / m^3 (World Bank by way of The Guardian.)

(The dollar sign seems to be a problem to display if I put one in front of both numbers, backslash doesn't escape.)

Comment Source:There are a lot of variables, maintenance in particular, but solar desalination is likely 10 to 100 times more expensive than piping rivers. Searching on "solar desalination cost" gives a figure of $1.52 - 2.05 / m^3 (World Bank by way of The Guardian.) (The dollar sign seems to be a problem to display if I put one in front of both numbers, backslash doesn't escape.) • Options 3. Sorry about those dollar signs. They're used in LaTeX to surround math equations, e.g. $E = mc^2$ gives$E = mc^2$In some blogs where dollar signs introduce equations I've used the html entity for dollars, &#36; but that doesn't seem to work here! Saving water that would otherwise run Comment Source:Sorry about those dollar signs. They're used in LaTeX to surround math equations, e.g. $E = mc^2$ gives$E = mc^2$In some blogs where dollar signs introduce equations I've used the html entity for dollars, &#36; but that doesn't seem to work here! Saving water that would otherwise run • Options 4. edited April 2016 Thanks. Was your comment cut off? Looking at it again, I think my original calculation was off. Here's a bit more detailed estimate: Per 1000 mi pipe, at 1 mph, the transit time is 1000 hr, ~8766hr/yr, so on the order of 10 times the volume of water in the pipe is delivered per year, or proportionally less for longer pipes. Also for 1mm pipe walls (flexible basalt fiber-reinforced plastic sheeting, ~1g/cc) and 10m diameter, the ratio of pipe mass to water mass would be 2500, though 0.25 mm (10mil) sheet would get up to a mass ratio of 10,000. The sheeting cost should be about 10-25 dollars per lb, call it USD 45K per tonne, and typing: "45 kdollar/tonne 1g/cc 1mm pi 10m 1000mi" into Frink gives about USD 2.3B per 1000mi pipe cost, which at a wild guess is about 23% of total project cost, so$10B/1000mi. That delivers about "pi(10m/2)^2 1mph" = 35m^3/s = 102 acrefoot/hr = 900kacrefeet/yr, which at 2ft water/yr would irrigate about 700 sq. mi. (a square 43km on a side).

[Edit: which works out to 1.11 dollar / cu. m for the first year, or 11 cents/cu. m with capital costs spread over 10 years, plus perhaps 5 to 10 cents / cu. m for operating costs and maintenance.]

The flow could run faster, the pipe could be bigger, less water would be needed with better use such as drip systems, and once an area has enough plants some of the evaporating water should rain back out, multiplying the effect of the water, so irrigating thousands of square miles should be possible -- but it looks like greening most of the Sahara would take more than one river and several decades.

Comment Source:Thanks. Was your comment cut off? Looking at it again, I think my original calculation was off. Here's a bit more detailed estimate: Per 1000 mi pipe, at 1 mph, the transit time is 1000 hr, ~8766hr/yr, so on the order of 10 times the volume of water in the pipe is delivered per year, or proportionally less for longer pipes. Also for 1mm pipe walls (flexible basalt fiber-reinforced plastic sheeting, ~1g/cc) and 10m diameter, the ratio of pipe mass to water mass would be 2500, though 0.25 mm (10mil) sheet would get up to a mass ratio of 10,000. The sheeting cost should be about 10-25 dollars per lb, call it USD 45K per tonne, and typing: "45 kdollar/tonne 1g/cc 1mm pi 10m 1000mi" into Frink gives about USD 2.3B per 1000mi pipe cost, which at a wild guess is about 23% of total project cost, so $10B/1000mi. That delivers about "pi(10m/2)^2 1mph" = 35m^3/s = 102 acrefoot/hr = 900kacrefeet/yr, which at 2ft water/yr would irrigate about 700 sq. mi. (a square 43km on a side). [Edit: which works out to 1.11 dollar / cu. m for the first year, or 11 cents/cu. m with capital costs spread over 10 years, plus perhaps 5 to 10 cents / cu. m for operating costs and maintenance.] The flow could run faster, the pipe could be bigger, less water would be needed with better use such as drip systems, and once an area has enough plants some of the evaporating water should rain back out, multiplying the effect of the water, so irrigating thousands of square miles should be possible -- but it looks like greening most of the Sahara would take more than one river and several decades. • Options 5. Saving water that would otherwise run into the sea is also being studied here in Southern California. One problem is that the flow is extremely intermittent: the occasional rain brings a big burst of water down the usually almost dry Los Angeles River. Comment Source:Saving water that would otherwise run into the sea is also being studied here in Southern California. One problem is that the flow is extremely intermittent: the occasional rain brings a big burst of water down the usually almost dry Los Angeles River. <img width = "350" src = "http://hildalsolis.org/wp-content/uploads/2015/10/Los_Angeles_River_Photo.jpg" alt = ""/> • Options 6. Some progress in LA: Los Angeles gets little rain, and what it does get occasionally arrives in the form of harsh, flood-generating storms, like the ones last week. After numerous destructive floods in the first third of the 20th century, the Army Corps of Engineers and the city’s public works department began building a flood-control infrastructure. It was designed to move storm water quickly off city streets and into the Pacific Ocean. All but seven miles of the 51-mile-long Los Angeles River was turned into an ugly concrete conduit that is usually empty. Flooding stopped, but at a cost. As the region grew, agriculture gave way to urban development, and more and more land was covered with an impermeable layer of pavement and buildings. This meant that even if a storm produced no more rainfall than one a decade earlier, it generated far more runoff. As the water flowed over the city’s hard surfaces, it collected more and more pollutants — animal waste, car oil, toxic chemicals and metals — and deposited them on the beaches and in the sea. Of course, Los Angeles was also importing huge amounts of water, drying out previously pristine areas far to the city’s north. The water-supply infrastructure imported water while the flood-control system exported it, and both processes ravaged the environment. By the late 1980s, storm water quantities were getting so high that the flood-control channels could no longer contain them. The authorities assumed their only alternative was to raise the cement walls still higher, which they did in the 1990s at a cost of$180 million.

Meanwhile, two environmental campaigners, Dorothy Green of Heal the Bay and Andy Lipkis of TreePeople, were telling anyone who would listen that the flood-control infrastructure should be reorganized to capture water, not cast it into the sea. If storm water is harvested and directed into aquifers, they argued, floods can be prevented. Then the stored water can be pumped when needed, treated and consumed.

For more see:

Comment Source:Some progress in LA: > Los Angeles gets little rain, and what it does get occasionally arrives in the form of harsh, flood-generating storms, like the ones last week. After numerous destructive floods in the first third of the 20th century, the Army Corps of Engineers and the city’s public works department began building a flood-control infrastructure. It was designed to move storm water quickly off city streets and into the Pacific Ocean. All but seven miles of the 51-mile-long Los Angeles River was turned into an ugly concrete conduit that is usually empty. > Flooding stopped, but at a cost. As the region grew, agriculture gave way to urban development, and more and more land was covered with an impermeable layer of pavement and buildings. This meant that even if a storm produced no more rainfall than one a decade earlier, it generated far more runoff. As the water flowed over the city’s hard surfaces, it collected more and more pollutants — animal waste, car oil, toxic chemicals and metals — and deposited them on the beaches and in the sea. Of course, Los Angeles was also importing huge amounts of water, drying out previously pristine areas far to the city’s north. The water-supply infrastructure imported water while the flood-control system exported it, and both processes ravaged the environment. > By the late 1980s, storm water quantities were getting so high that the flood-control channels could no longer contain them. The authorities assumed their only alternative was to raise the cement walls still higher, which they did in the 1990s at a cost of \$180 million. > Meanwhile, two environmental campaigners, Dorothy Green of Heal the Bay and Andy Lipkis of TreePeople, were telling anyone who would listen that the flood-control infrastructure should be reorganized to capture water, not cast it into the sea. If storm water is harvested and directed into aquifers, they argued, floods can be prevented. Then the stored water can be pumped when needed, treated and consumed. For more see: * Jacques Leslie, [Los Angeles, city of water](http://www.nytimes.com/2014/12/07/opinion/sunday/los-angeles-city-of-water.html), _New York Times_, 6 December 2014. 
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7.

The L.A. initiative is an interesting scheme, though no lawyer could recommend a client turning a significant part of a property into an intermittent wetland under the current regulations -- it would mean forgoing any development or reuse of that part of the property, while continuing to be liable for property taxes that don't take such usage restrictions into consideration.

The idea of permeable paving, though, is one I think should be encouraged indeed, usually required.

Permiable paving reminds me of "gabions" [image search], which originally in the Middle Ages were baskets of earth stacked to make fortifications,but today are often expandable plastic or steel sheets welded into honeycomb structures to make pavements, or rocks in stacked rabbit-wire cages. The general strategy of containing found compressive materials such as earth and rock within tensile structures of steel or plastic mesh or sheet allows building impressive and extraordinarily durable structures at very low cost. When built with stones, particularly river- or coarse stones, gabions are highly water-permeable.

Now taking a digression here, "gabions" remind me of a physics paper that used the term to refer to doubly-ruled hyberbolic structures, the dog-bone shape that is the norm for water-tower supports and high towers built from straight structural members. I looked it up, and while it has some cranky signs (corresponding author is an orthopedist, published in the "New Journal of Physics"), but that is IOP published, the other seven authors include a West Point physics professor and various sorts of engineers, and while it appears to be written in a dialect of Martian with which I am personally unacquainted, skimming it, it seems like they know what they're talking about, (though I certainly don't), and there are a lot of interesting things such as setting off to find a clear understanding of the mechanism behind the Stern Gerlach effect, executable physical simulation code, systems/cybernetic diagrams, spin networks, Grassmannian whatsits and suchlike catnip. Is it interesting or ...? (Link to 96 page PDF: Practical recipes for the model order reduction, dynamical simulation and compressive sampling of large-scale open quantum systems

Abstract:

Abstract. Practical recipes are presented for simulating high-temperature and nonequilibrium quantum spin systems that are continuously measured and controlled. The notion of a spin system is broadly conceived, in order to encompass macroscopic test masses as the limiting case of large-j spins. The simulation technique has three stages: first the deliberate introduction of noise into the simulation, then the conversion of that noise into an equivalent continuous measurement and control process, and finally, projection of the trajectory onto state-space manifolds having reduced dimensionality and possessing a Kähler potential of multilinear algebraic form. These state-spaces can be regarded as ruled algebraic varieties upon which a projective quantum model order reduction (MOR) is performed. The Riemannian sectional curvature of ruled Kählerian varieties is analyzed, and proved to be non-positive upon all sections that contain a rule. These manifolds are shown to contain Slater determinants as a special case and their identity with Grassmannian varieties is demonstrated. The resulting simulation formalism is used to construct a positive P-representation for the thermal density matrix. Single-spin detection by magnetic resonance force microscopy (MRFM) is simulated, and the data statistics are shown to be those of a random telegraph signal with additive white noise. Larger-scale spin-dust models are simulated, having no spatial symmetry and no spatial ordering; the high-fidelity projection of numerically computed quantum trajectories onto low dimensionality Kähler state-space manifolds is demonstrated. The reconstruction of quantum trajectories from sparse random projections is demonstrated, the onset of Donoho–Stodden breakdown at the Candès–Tao sparsity limit is observed, a deterministic construction for sampling matrices is given and methods for quantum state optimization by Dantzig selection are given.

Comment Source:The L.A. initiative is an interesting scheme, though no lawyer could recommend a client turning a significant part of a property into an intermittent wetland under the current regulations -- it would mean forgoing any development or reuse of that part of the property, while continuing to be liable for property taxes that don't take such usage restrictions into consideration. The idea of permeable paving, though, is one I think should be encouraged indeed, usually required. Permiable paving reminds me of "[gabions](https://www.google.com/search?biw=1299&bih=583&tbm=isch&sa=1&q=medieval+gabion&oq=medieval+gabion)" [image search], which originally in the Middle Ages were baskets of earth stacked to make fortifications,but today are often expandable plastic or steel sheets welded into [honeycomb structures](https://www.google.com/search?biw=1299&bih=583&tbm=isch&sa=1&q=geocell+pavement&oq=geocell+pavement) to make pavements, or rocks in stacked rabbit-wire [cages](https://www.google.com/search?biw=1299&bih=583&tbm=isch&sa=1&q=medieval+gabion&oq=medieval+gabion). The general strategy of containing found compressive materials such as earth and rock within tensile structures of steel or plastic mesh or sheet allows building impressive and extraordinarily durable structures at very low cost. When built with stones, particularly river- or coarse stones, gabions are highly water-permeable. Now taking a digression here, "gabions" remind me of a physics paper that used the term to refer to doubly-ruled hyberbolic structures, the dog-bone shape that is the norm for water-tower supports and high towers built from straight structural members. I looked it up, and while it has some cranky signs (corresponding author is an orthopedist, published in the "New Journal of Physics"), but that is IOP published, the other seven authors include a West Point physics professor and various sorts of engineers, and while it appears to be written in a dialect of Martian with which I am personally unacquainted, skimming it, it seems like they know what they're talking about, (though I certainly don't), and there are a lot of interesting things such as setting off to find a clear understanding of the mechanism behind the Stern Gerlach effect, executable physical simulation code, systems/cybernetic diagrams, spin networks, Grassmannian whatsits and suchlike catnip. Is it interesting or ...? (Link to 96 page PDF: [Practical recipes for the model order reduction, dynamical simulation and compressive sampling of large-scale open quantum systems](http://web.eecs.umich.edu/~hero/Preprints/PracticalRecipes.pdf) Abstract: >Abstract. >Practical recipes are presented for simulating high-temperature and nonequilibrium quantum spin systems that are continuously measured and controlled. The notion of a spin system is broadly conceived, in order to encompass macroscopic test masses as the limiting case of large-j spins. The simulation technique has three stages: first the deliberate introduction of noise into the simulation, then the conversion of that noise into an equivalent continuous measurement and control process, and finally, projection of the trajectory onto state-space manifolds having reduced dimensionality and possessing a Kähler potential of multilinear algebraic form. These state-spaces can be regarded as ruled algebraic varieties upon which a projective quantum model order reduction (MOR) is performed. The Riemannian sectional curvature of ruled Kählerian varieties is analyzed, and proved to be non-positive upon all sections that contain a rule. These manifolds are shown to contain Slater determinants as a special case and their identity with Grassmannian varieties is demonstrated. The resulting simulation formalism is used to construct a positive P-representation for the thermal density matrix. Single-spin detection by magnetic resonance force microscopy (MRFM) is simulated, and the data statistics are shown to be those of a random telegraph signal with additive white noise. Larger-scale spin-dust models are simulated, having no spatial symmetry and no spatial ordering; the high-fidelity projection of numerically computed quantum trajectories onto low dimensionality Kähler state-space manifolds is demonstrated. The reconstruction of quantum trajectories from sparse random projections is demonstrated, the onset of Donoho–Stodden breakdown at the Candès–Tao sparsity limit is observed, a deterministic construction for sampling matrices is given and methods for quantum state optimization by Dantzig selection are given.
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edited April 2016

I've no idea what I read by John Siddles but I do remember I enjoyed it. He's been featured in the pop sci and other press probably cos he's a sawbones as well as being an author of stuff like that dense bucket of jargon :).

Comment Source:I've no idea what I read by John Siddles but I do remember I enjoyed it. He's been featured in the pop sci and other press probably cos he's a sawbones as well as being an author of stuff like that dense bucket of jargon :).
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edited April 2016

It turns out Sidles is one of the inventors of magnetic resonance force microscopy and co-director of the U. of Washington Quantum System Engineering Lab.

He also seems to have had a project to politely annoy Scott Aaronson in the comments on his blog, Shtetl-Optimized. (Aaronson is about to move from MIT to run the quantum computing lab at U. of Texas.) At more than one point Aaronson banned Sidles from his blog for thee months for being too courteous, supporting his arguments with too many citations of famous physicists and just generally being right.

Comment Source:It turns out Sidles is one of the inventors of magnetic resonance force microscopy and co-director of the U. of Washington Quantum System Engineering Lab. He also seems to have had a project to politely annoy Scott Aaronson in the comments on his blog, Shtetl-Optimized. (Aaronson is about to move from MIT to run the quantum computing lab at U. of Texas.) At more than one point Aaronson banned Sidles from his blog for thee months for being too courteous, supporting his arguments with too many citations of famous physicists and just generally being right.
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edited April 2016

Thanks for that Enon, I missed any like while I've found the Aaronson DWave challenges to be v. informative fun. As a complete beginner at QM who probably needs to know at lot more complexity theory one of the most useful recent reads for me was Aaronson's survey of approaches to npcompleteness:

http://scitation.aip.org/content/aapt/journal/ajp/40/11/10.1119/1.1987001

At some point I'd like to know what +Jacob Biamonte thinks the current state of argument is.

Comment Source:Thanks for that Enon, I missed any like while I've found the Aaronson DWave challenges to be v. informative fun. As a complete beginner at QM who probably needs to know at lot more complexity theory one of the most useful recent reads for me was Aaronson's survey of approaches to npcompleteness: http://scitation.aip.org/content/aapt/journal/ajp/40/11/10.1119/1.1987001 At some point I'd like to know what +Jacob Biamonte thinks the current state of argument is.