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Parsas Decem land map

So this is a small map of all the continents on the small planet of Parsas Decem. As far as most of the rivers go, I’ve got it figured out. What I’m wondering is, can salt water flowing in from the sea be filtered naturally by the soil, perhaps with specific desalinating minerals, into fresh water? If I can, I’ll try to post the map of just the north eastern quarter of Daichi.

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  • $\begingroup$ Welcome to worldbuilding. Please take the tour and visit the help center to better understand our community. Also, please use the edit function to edit your question, we are not a forum where you post below your initial post to further add information, this is why I have deleted your "answer". I also don't see the relation between your question and the image, so I would consider removing it. $\endgroup$ – L.Dutch Feb 9 at 5:35
  • $\begingroup$ No it cannot, and moreover you did not explain why you need this to happen: maybe there are other ways to solve the real problem. $\endgroup$ – AlexP Feb 9 at 5:42
  • $\begingroup$ Are you familiar with the history of the Baltic Sea since the last glacial maximum? It has experienced all of these regimes. $\endgroup$ – Jasper Feb 9 at 5:42
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    $\begingroup$ On an off-note: you seem to have multiple rivers that are combined in- and outflows - is this by design or by accident? Usually water only flowa into one direction; streams join into one, becoming bigger; lakes have multiple inlets but only one outlet $\endgroup$ – dot_Sp0T Feb 9 at 7:49
  • $\begingroup$ For the most part water source comes down from the frigid snow of Akull which is fresh. There’s an area where it seems to flow into Rants which is a flooded swampy marshland, and then I suppose brackish water flows south from where they meet but I’m thinking I’ll need a lake there. I guess the river that comes in from beneath Walnot and Tachiki will have to be salty rivers. $\endgroup$ – Bett Struble Feb 9 at 9:36
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Saltwater does not move far inland, you are chasing a problem that doesn't exist. Saltwater intrusion of more than a kilometer is all but unheard of, and then only in the driest locations and only affecting deep wells. Saltwater is also displaced outward and downward by fresh water, the fresh water is renewed by rain anywhere inland. Look at the lower picture an example of measured salt water intrusion. Saltwater permeating inland is measured in feet.

Unless you have and an inland sea that is not shown or have extreme flooding salt water intrusion is not an issue, and if you do that is a very different question.

enter image description here

enter image description here

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can salt water flowin in from the sea be filtered naturally by the soil, perhaps with specific desalinating minerals, into fresh water?

You are looking for a way to naturally desalinize water.

Sorry to disappoint you, but it requires energy to happen, thus I don't think it can happen by simple filtration.

Desalination is a process that takes away mineral components from saline water.

The closes you can get in a natural environment is one of the following:

First reverse osmosis

The leading process for desalination in terms of installed capacity and yearly growth is reverse osmosis (RO). The RO membrane processes use semipermeable membranes and applied pressure (on the membrane feed side) to preferentially induce water permeation through the membrane while rejecting salts. Reverse osmosis plant membrane systems typically use less energy than thermal desalination processes.

Or also freeze-taw

Freeze-thaw desalination uses freezing to remove fresh water from salt water. Salt water is sprayed during freezing conditions into a pad where an ice-pile builds up. When seasonal conditions warm, naturally desalinated melt water is recovered. This technique relies on extended periods of natural sub-freezing conditions.

Or, finally, solar evaporation

Solar evaporation mimics the natural water cycle, in which the sun heats the sea water enough for evaporation to occur. After evaporation, the water vapor is condensed onto a cool surface.

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  • $\begingroup$ Well what if there were natural fresh springs feeding the rivers that start salty? Would you say it’s possible for the salt levels to become essentially negligible if there are enough fresh springs on the way? Or would the salt water likely always be salty? It’s fine if they’re not all fresh, I just need to know the lay of the land before any stories can happen around them $\endgroup$ – Bett Struble Feb 9 at 9:43
  • $\begingroup$ @BetteStruble, this is a different question than what you asked. You asked about filtration, not dilution. $\endgroup$ – L.Dutch Feb 9 at 12:18
  • $\begingroup$ if there is a natural spring your river will not be salty. $\endgroup$ – John Feb 9 at 15:05
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Probably it is not what you asked for, but you could find it interesting
This article explains that for the ancient Easter Island populations, the main water sources were brackish-water pools near the sea.

the Rapanui probably got at least some of their drinking water from places along the coast where fresh groundwater seeped out of the island’s bedrock and into the sea. The resulting mixture would have been brackish but safe to drink, and it could have sustained populations of thousands on an island with few other reliable sources of fresh water

I know that it is not a desalinization of sea water (of course it is the opposite, the partial salinization of underground water), but it could sustain some settlements along the coast and far from rivers, if the soil is too hard to dig wells far from the sea.
And if the brackish water has a bad taste, you can always use it to brew beer :)

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Well no, but...
Salt water is more dense than fresh. If you have a difficult region for wells, say very sandy or otherwise unable to keep wells from crumbling, you could flood the area with salt water that would sink and raise up the fresh water which could be harvested off the top.

(might have to do this experiment myself: take a pot or bucket and fill it one quarter with fresh water and then halfway with sand (so that sand is basically wet but no way to take a straw and suck out just water); then add seawater until it displaces the freshwater which rises above the sand and can be siphoned off)

I don't know the long term viability of this plan but as long as the ground is saturated with the seawater all the rain or aquifer seepage will be on top and able to be collected.

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    $\begingroup$ You need something to prevent salt following the concentration gradient. $\endgroup$ – L.Dutch Feb 9 at 8:28
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Already said, desalination requires energy. I would also add that if any subsoil filtering system exists, where does the salt go to? From your description, it must accumulate until the filtration system is no longer operable. The inhabitants must have mined that salt on a regular basis, but that necessitates some mining technology, as well as knowing about such filtration system in the first place.

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