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In a previous question I asked if a world similar to that envisioned in the Mars of Edgar Rice Burroughs / H G Wells could exist? And if so would canals be a practical way to make the planet habitable over the long term?

One of the potential issues identified with such a scenario was the prospect of salinization of the canals

How best can the Martians prevent salinization of their canal network? Pipes can be used in places but canals are needed for my story and for transportation. Assume that The Martians have modern twenty first century technology, plenty of money (hey it’s an existential threat to the civilization) and a lot of time (decades – centuries). Conveniently in the hemisphere and latitudes of interest it can be assumed that there is sufficient head of water and suitable gradient to generate a flow over a wide area of the canal network from the melt waters in the sub Artic regions to the dry by fertile land in the subtropics.

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    $\begingroup$ Perhaps Martian Red Weed thrives upon or bio-accumulates salts. Perhaps it was designed to do so, converting salty oceans into freshwater oceans and a salty layer of coal. Them Martians are pretty smart evil dudes. $\endgroup$ – user535733 Dec 21 '19 at 21:09
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If the "Martians" living in this world that resembles the fictional Mars of many early 20th century science fictions stories have any sense, they will do a lot more to save their planet than just build canals.

Percival Lowell believed that Mars was drying up as it lost atmosphere including water vapor in that atmosphere. So he imagined that the Martians created the canal network to optimized their use of water.

That makes sense, but that is not the only think the Martians could do to delay or prevent ecological collapse.

For example, the Martians could prevent the loss of atmospheric hydrogen, and thus water, by putting an airtight roof over their atmosphere. Putting an airtight roof over their atmosphere all over the planet would be a very big project, of curse, so maybe they would just put an air tight roof over part of their planet.

The Martians could build ecologically closed cycle "moon bases" on Mars, and convert their civilization to an entirely enclosed ecology within their vast sealed cities. Perhaps they would use hydroponics and aeroponics to grow their food indoors inside their "moon base" cities on Mars. Maybe they would use 3D food printers or other food synthesizers to create their food.

And the Martians could fight atmospheric loss and water loss by importing atmospheric gases and water from other astronomical bodies. Comets consist largely of frozen gases. So the Martians could send expeditions to comets to divert them into orbit around Mars and send shipments of desired gases and water down to the surface of Mars until the comets were used up, then divert other comets.

And it seems to me that your "Martians" living on a planet that resembles the early fictional Mars could do those things as well as building a canal network.

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  • $\begingroup$ The Martians decided to build canals to resolve their issue but are worries about salt. In my fictional world the reason for the water shortage is because the climate is colder and all the water is freezing at the poles. $\endgroup$ – Slarty Dec 21 '19 at 21:07
  • $\begingroup$ @Slarty Then your planet may have to be much larger than Mars, though possibly much smaller then Earth. Mars might not have a high enough escape velocity to hold onto a dense atmosphere for billions of years. The minimum size for a habitable planet is discussed in Habitable planets for Man, Stephen Dole, and articles like: iopscience.iop.org/article/10.3847/1538-4357/ab2bf2 -- earthsky.org/space/… $\endgroup$ – M. A. Golding Dec 22 '19 at 18:29
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It no longer rains on Mars.

Salinization on Earth happens when saline groundwater can infiltrate the soil, or when sparse rains dissolve soil salts and let them move to the surface.

It never rains on Barsoom. The canals (glass lined, using the Old Latrobe method) do not allow water in the canals to contact soil. The water in the canals is lifted there by the great polar pump which taps a reservoir of fresh meltwater. A lot is lost to evaporation and some of this winds up in high cirrus clouds, which accumulate at the poles and release the water as snow.

The polar reservoir is gradually being depleted. It is not a system that will last forever. The Martians know this and try to conserve. Unused canals are purged of water during disuse. These long empty glass-lined channels are then ideally suited for high speed skateboard travel.

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    $\begingroup$ they will still pick up salt from wind blow sediment but this effect will be very minor on the time scale of a civilization. $\endgroup$ – John Dec 21 '19 at 17:42
  • $\begingroup$ @John - I was thinking about that. It is interesting to consider whether a lip on the canal might be built to encourage wind to go up and over. $\endgroup$ – Willk Dec 21 '19 at 18:26
  • $\begingroup$ only if it is a tube not a canal. $\endgroup$ – John Dec 21 '19 at 18:47
  • $\begingroup$ @John - I suspect the largest risk of windborne dirt for a waterway would be pieces that tumble along the surface and lodge in depressions, the canal being one. I have seen open wells and waterways with low walls that I think prevent that - also they prevent animals and people from falling in. Probably low walls would do a lot to keep dirt out. Windborne dust at altitude would have no more reason to fall into the canal than anywhere else. $\endgroup$ – Willk Dec 21 '19 at 19:24
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    $\begingroup$ The use of glass lined canals explains "why" the Martians developed the powerful heat ray that H.G. Wells described.... $\endgroup$ – Thucydides Dec 22 '19 at 5:23

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