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Color legend: The brown shapes are hills, the darker the brown the higher the mountains and the highest peaks I've made white. They are mostly clustered on the east and west edges. The green shows forests and the darker green is jungle.

I am creating my first map for a world I am building, but I am having some difficulty working out the rivers. I did some research and 'feel' these are correct, but was hoping someone with more geographical knowledge might be able to point out if anything is glaringly wrong?

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    $\begingroup$ Land height is extremely important in determining where a river should go. Just to be sure, is your map a topology one or is it more general? Is it possible to have something more detailed, regarding mountains, plains, canyons...? $\endgroup$ Jun 9, 2022 at 9:21
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    $\begingroup$ Since people can skip comments, I've added yours to your question. Hopefully this'll help answerer to understand everything :). $\endgroup$ Jun 9, 2022 at 9:44
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    $\begingroup$ One easy way to check for inconsistencies is to pencil in the direction that the river is flowing. Do this for every tributary as well, and on longer rivers do it multiple times along its length. Inconsistencies will become apparent, like arrows pointing towards each other or uphill. $\endgroup$
    – bta
    Jun 9, 2022 at 18:59
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    $\begingroup$ What is the scale of this map? Approximately how big is it? Basins without outflows usually only tend to form in continental interiors, where the climate is relatively dry and that there's not enough precipitation to cause them to overflow and cut a new channel to the sea. $\endgroup$ Jun 9, 2022 at 20:33
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    $\begingroup$ It appears that some rivers flow uphill. And some become narrower instead of wider. And no rivers going directly from the mountains to the see is weird. $\endgroup$
    – gre_gor
    Jun 10, 2022 at 10:09

5 Answers 5

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Assuming that your map is a continent, and the black surroundings are the sea.

Most of your rivers stay inland. That does not feel realistic. Rivers generally run towards the sea, or are tributary to a river that does.

The way you designed your map, those large lakes that are fed by some of the larger rivers will be very salty.

Remember that rivers are fed by rainfall or by melting snow, which is basically the same. That rainfall obviously comes from evaporating water elsewhere (the sea, mostly).
As the water runs down the countryside, it dissolves a lot of minerals, carrying them downstream. The minerals don't evaporate with the water, so the basin where everything flows becomes increasing mineral rich. That's why the sea is salty, and thus every basin without an outlet apart from evaporation will accumulate salt, minerals and dirt.

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The big question is how old is the island.

Rivers are fairly simple really. Any rainfall on your island will flow downhill and collect at the lowest points. Anywhere that enough water collects up while flowing will become a river.

But then you need to add time to the mix. Water flows down to the lowest point, but then it has to evaporate. If it doesn't evaporate as fast as it's flowing in, then the water level rises.

Furthermore, flowing water erodes everything, so a river will eventually carve a channel down to sealevel. ("Eventually" meaning potentially hundreds of millions of years depending on how high the ground started, and how hard the rock is.)

So...

This looks like an island that's at most like a hundred thousand years old that has either low precipitation, or a high evaporation rate.

If precipitation vs evaporation isn't pretty tightly balanced on this island (which will be hard to maintain long-term) then those lakes your rivers drain into will either dry up or fill up. In the former case you now probably have a desert island. In the latter case they either find a way out to the sea, or your island becomes a soup bowl.

That system in the southwest is going to be particularly unstable. According to your coloring the difference in height between the river's close approach to the sea and the inland lake it ultimately appears to drain into is pretty small. One year with extra rain raising the lake level and the river is going to jump its banks at that inlet and carve a new channel. And then that whole section down to the lake is going to reverse direction and the lake will drain into the ocean.

Is it realistic given the contours you've designed? Reasonably. Is it stable? Heck no. The inhabitants of this island are likely in for some major upheaval over the next thousand years or so as the rivers create more stable pathways to sealevel.

Unless it's a volcanic island and there are cracks in the rock under those lakes leading out to the sea, in which case those cracks will erode bigger over time and eventually you'll have sinkholes opening up at unpredictable locations.

None of this is necessarily bad, and may even be preferable for a fantasy story. Plenty of opportunity for shifting borders and rescuing whole villages from sudden shifts in water flow.

But if that's not what you want then think through some fluctuations in water level and what will happen with those collection points. Which way will they go when they overflow? They'll carve a channel to the next lowest point when they do. Repeat until there's nowhere lower for it to escape to.

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    $\begingroup$ I'm really happy to read this comment as that's actually part of my plan when trying to build the map. I'm not particularly well versed in geography but my aim was for the civilisation to slowly dry up and lose a lot of its tenable water to the sea. Their culture reflects the last time this sort of event happened, when the land was mostly flooded and they don't realise till its too late. I was going to redisign that south area so several rivers flow directly to the sea and get rid of that lake, as others have pointed out it doesn't make sense, but maybe I should keep it for this reason? 🤔 $\endgroup$
    – EmRy
    Jun 9, 2022 at 19:25
  • $\begingroup$ @EmRy So like it's a desert island normally and the rivers and lakes are the result of a few years of wet weather, possibly cold enough to collect up some glaciers in the high mountains to keep the water flowing for a while? I'm not sure you have quite enough really tall mountains for that. Both because you'd need a big rain shadow to keep from flooding the interior, and enough glacier area to maintain the flow. Keeping the water going long enough for everyone to forget that it's usually dry without the water escaping the lakes will be tricky. Or are the rivers the start of a wet period? $\endgroup$
    – Perkins
    Jun 10, 2022 at 15:26
  • $\begingroup$ In my mind it started out as quite a waterlogged continent, the central desert perhaps being an ocean or very large lake once, but over time as the planet heats up and ice from the mountain thaws but eventually runs out the rivers run dry and there's a drought crisis. I'm not sure how feasible that is or if it would work better the other way around. I can always make the existing mountains taller and add some if that helps? The map is far from finished for this reason, I wanted to get the bare bones right before I start tidying it all up $\endgroup$
    – EmRy
    Jun 10, 2022 at 15:41
  • $\begingroup$ @EmRy You'll need high mountains around the edge of the island on at least the side of the prevailing winds to create a rain shadow. Otherwise islands in the middle of big oceans tend to get quite a bit of precipitation. $\endgroup$
    – Perkins
    Jun 15, 2022 at 22:54
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I am no professional at geography, but I will try my best to provide comments.

General comments on this map:

  • Most rivers are inland, this is not very realistic and you will end up having undrinkable water unless purified extensively due to large amounts of salt that remain. Try having more rivers go out to sea.
  • You have many mini islands below this large continent, try making some small rivers there on some islands.
  • Your large basin or reservoir near the top left corner of the island, with rivers branching out is well placed! But you have 1 or 2 rivers going into the sea if you want.
  • Your island has way too many forests and jungles, try placing some deserts, maybe 1 or 2 medium sized ones, one on the top right or the island, the other on the bottom.
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  • $\begingroup$ Extra tip, try having 1 or 2 rivers going into the sea @EmRy :) This comment is optional, you can choose to add them or not. $\endgroup$
    – DialFrost
    Jun 10, 2022 at 1:08
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Water flows from higher level to lower level.

No contours

If you show contour lines on the map, drawing river will be very easy as river flow will be normal to a contour line.

No direction of flow

From direction of flow, one can determine if it is a main river or a distributary or a tributary. It is not shown in your map.

No Source

Normally source of a river is a glacier or tributaries. No sources are clear in the map.

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    $\begingroup$ I think this is worth more a comment requesting details than an answer. The asker's asking for the geography of the world, not about the map itself. $\endgroup$ Jun 9, 2022 at 15:29
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    $\begingroup$ I disagree with the last point. Most rivers are formed as smaller rivers merge to form bigger ones, with the ultimate sources being small mountain streams. If the lake is the "source", either the lake is drained quickly and you have no more river, or something is refilling the lake and that something should more accurately be considered the source. $\endgroup$
    – chepner
    Jun 9, 2022 at 18:00
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    $\begingroup$ Most commonly, you have smaller trickles from springs or meltwater starting in the mountains or hills, and as they collide on the way down they form larger trickles, then streams, then rivers. $\endgroup$
    – chepner
    Jun 9, 2022 at 18:01
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    $\begingroup$ Voted up for the comment about river flow being normal to contour lines. That's gold. $\endgroup$ Jun 9, 2022 at 19:02
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I addition to the answers given above, concerning water flow in general, rivers in more flat areas usually tend to bend very much, way more than yours do.

Take a look at this video about this phenomenon. It also gives a general formula about the "bendiness" of a river depending on the width of the current.

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