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

For current purposes such a world would have gravity and atmosphere suitable for human life, but would have limited supplies of water most of which would be locked in the ice caps. Each ice cap would be surrounded by a zone with some water but which was too cold for agriculture. North and south of the equator would be a warm but very dry desert zone where it was warm enough for agriculture but without enough water.

Background information: Assume that water was originally more widely distributed, but the planets orbit was disturbed by the passage of a brown dwarf star through or near to its parent star causing a change in its orbit. Although the change in orbit had catastrophic effects, civilization was able to survive, but is faced with the problem that the limited water available is increasingly being frozen out at the poles generating the need to ship water from cold wet regions to warm dry ones on a planetary scale.

Also assume a civilization roughly equivalent to our own (and no magic!).

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One of the major issues in transporting water long distances via canals or other means for agriculture is salinization. This is particularly evident in large parts of the former Soviet Union, particularly where large amount of water were diverted from the Aral sea. Not only is the exposed sea bed a toxic wasteland of salt flats from the water evaporating away, but the large areas irrigated by canals have also become heavily contaminated by salt through the process of salinization. (The incredibly poor agricultural practices of collective farming, unrestrained use of fertilizers and pesticides didn't help either).

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Aral sea, before and after

So the conception of open air canals along Mars, lined with lush agricultural fields and forests (hence their discovery by human astronomers in the 1800's...) is sadly wrong headed. Unlike the Nile River, which floods the banks of the river and the delta, flushing away salt build up and renewing the soil with fresh silt, canals will have a slow and relatively constant flow of water.

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Romantic conception of the Martian canals

So how will the Martians survive? The best way to deal with this is to transport the water from the poles to the agricultural zones through pipelines, where the water is segregated from the soil. The water is also protected from environmental contamination (i.e. dirt, pathogens or agricultural runoff) entering the stream, until it reaches its destinations.

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Typical water pipeline from the Great Lakes to a mid sized Canadian city. This is one of at least 4 pipelines (from two separate lakes)

The Martians can choose to store the water in whatever system is suitable, such as artificial lakes, pumping it into sub surface aquifers or building giant cisterns to hold it until needed. In order to utilize the water for agricultural purposes, the best method for long term conservation of soil (particularly given the equatorial climate is warm and dry) is to use "trickle" or "drip" irrigation. Here the water is pumped through permeable pipes laid along the rows of crops and water literally drips out of the pipe into the root systems of the plants. This conserves water, by precisely metering it to the plants, and minimizes the salinization of the soil in the longer term.

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Drip irrigation in the field

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Israeli farm from the air. The Martian farms can look like this

The other major issue is the energy required to do all this. A system of pipelines will need "melting stations" at the [poles to turn the ice into liquid water. The water then needs to be pumped up to 5000+ km from the poles to the farmlands in the equatorial zones, then processed for Martian consumption, or pumped through the network of drip pipes into the fields. Extra energy will be needed to pump water into and out of storage (if artificial lake are carved into hilltops, water can flow to the end user via gravity, but you still need to pump it into the lakes first).

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Solar mirrors over Mars. You need energy on this scale for the project to work

The Martians can use nuclear energy, solar power, geothermal energy or whatever else is common in your setting. The energy source needs to be reliable and large scale, much like the baseline energy grid on our world.

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  • $\begingroup$ Seems the key issue that I had overlooked is salinization. A civilization as advanced as ours would know this would be an issue so could presumably recreate conditions needed for a Nile flood like event if there was a sufficiently large depression that could be used as a drain. Water in this new salt sea would eventualy evaporate and be frozen out at the poles again. $\endgroup$ – Slarty Sep 11 '17 at 9:55
  • $\begingroup$ If pipelines are much better than canals then why do we have any irrigation canals? One advantage of canals would be creating an easy means of transportation, which is why I need them. So what would favour canals over pipes? $\endgroup$ – Slarty Sep 11 '17 at 10:15
  • $\begingroup$ Irrigation canals are much cheaper than pipelines, so long as you are simply calculating the cost of labour and machinery. Shipping canals would actually be quite expensive on the scale you are talking about since they would have to be lined with concrete, not to mention systems of locks to bring water and shipping over areas of changing elevation. $\endgroup$ – Thucydides Sep 11 '17 at 16:57
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Meridional circumference of Mars = 21244 km. So from pole to equator = 21244 / 4 = 5311 km.

Top 5 canals by length

Rank Name of Canal Length Connection Country Locks
1 Grand Canal 1,776 Km Beijing-Hebei-Shandong-Jiangsu-Zhejiang-Hagzhou China 24
2 Qaraqum Canal 1,375 Km Amu Darya-Karakum Desert Russia
3 Saimaa Canal 814 Km SaimaGulf of Finland Russia 8
4 Eurasia Canal 700 Km Black Sea-Kuma Manych Depression Russia 13
5 Manych Ship Canal 700 km Black Sea-Caspian Sea Russia 6
6 Erie canal 584 km Albany-New York-Buffalo USA

Pipelines?

The United States lead the list of countries by the total length of pipeline network featuring a network of pipelines with a total length of 2,225,032 km. 240,711 km of the pipeline network transport petroleum products and 1,984,321 km natural gas.

The list of countries by the total length of pipelines is continued with Russia on rank 2 featuring 259,913 km and Canada on rank 3 with a total length of 100,000 km.

Aqueducts?

The Catskill Aqueduct carries water to New York City over a distance of 120 miles (190 km), but is dwarfed by aqueducts in the far west of the country, most notably the Colorado River Aqueduct, which supplies the Los Angeles area with water from the Colorado River nearly 400 km to the east and the 701.5 mi (1,129 km) California Aqueduct, which runs from the Sacramento-San Joaquin River Delta to Lake Perris.

I think your best bet would be an aqueduct. The term refers not to a single structure but a system - this can include canals, pipelines, reservoirs and other structures along the way. It would be a multigenerational undertaking, I think. But it could be done.

I learned about qanats on the Worldbuilding site! How deep can, historically or realistically, aqueducts and/or underground pipeline systems get? I think any fictional Martian system should include qanats along its stretch. Because it will be nice and cool in the qanat underground, and various things will take refuge there as the planet dies around them.

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    $\begingroup$ Also take into account that Mars is mostly downhill from south pole to north pole so getting water from the northern ice cap will present a little more challenge than retrieving it from the south. $\endgroup$ – user38070 Sep 10 '17 at 22:54
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Yes such a world could exist and canals could then be used as a means to transport the water required.

Although canals would probably feature in places they would not always be suitable or necessary. Pipes or enclosed lined canals would be preferable in areas where there were high levels of salt contamination in the ground such as dried sea beds and salt flats or where large obstacles such as hills or mountains would make a surface canal impractical. Pre-existing features such as old river valleys, depressions and canyons might be repurposed to allow water to flow again. Dams and reservoirs might be constructed in suitable higher altitude areas to allow controlled seasonal inundation of agricultural land to prevent the build-up of salts in the soil provided a suitably low lying area was also available as a drain.

One important aspect would be the amount of time that it would take to transform the climate from the original warm minimal water world to the new warm desert - cold ice cap world. Such a process would take hundreds of years or more likely thousands depending on circumstances. If the process was relatively slow civilization could adapt more easily by extending waterways decade by decade, but if the change were rapid then adaption would be much harder and costly.

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