Once again help needed on a map and the courses of Rivers
I haven't been here in a while due to being dreadfully busy with schoolwork, but lately I've found the time to start working on my fantasy world again, and once again found myself facing many of the dilemmas I was struggling with before. So, I decided to wander to this fine site again in search of answers. I would really appreciate any assistance
Last spring I posted a map here (Advice needed concerning a fantasy map and the courses of rivers :)) looking for help in putting my map in at least a somewhat realistic shape, and got lots of great advice. Now that I have started working on it again, and have made quite a bit of revisions to the map, I have once again run into the believability issue. Something on my map just feels off somehow.
So that anyone doesn't have to go read the last thread, I'll explain the situation again:
The continent on the map is pretty enormous, 1 centimeter on the map represents a 1000 kilometer stretch of land. Which means both that the great northern forest is absolutely enormous, and that the great river flowing out of the forest and into the south must flow over 4500 kilometers to reach the sea (as opposed to the only 1000 kilometer distance to the northern sea), so there must be some pretty enormous elevation differences forcing the River to make such a detour, but such elevations would create their own difficulties to the forest...
I am aware that having such an enormous forest so far north and practically surrounded by mountains is practically impossible, which is why I've originally handled the issue by making the forest a very supernatural place. It gets much more rain than should ever be possible (due to being very saturated with dark magical energies and such), so this magical solution would certainly explain the impossible location of the forest. But I'm still wondering whether some kind of at least remotely believable explanation for the forest could be possible. I just prefer to avoid magical phenomena in world-building unless it's necessary.
I attached to version of the map here to illustrate my points. One is a modified version of my previous map (sorry about the poor quality of the picture, I did the modifications in Windows paint :p) and the other one is exactly the same, except with some numbers added for clarification purposes.
As you can see, the Great forest (number 3) is surrounded by mountains (number 1) and hills (number 2) in the west, and more hills in the east and north (number 4). I've been thinking that the prevailing winds in the area come from the east, bringing clouds from the ocean and traveling to the west, so the biggest obstacle to the rainclouds would therefore be the eastern hills. So technically if those hills (number 4) were low enough, perhaps the rainclouds could pass over them, flow over the forest, and then be stopped by the western hills which are higher (number 2) and rain down.
But the problem with this approach is that the forest itself must be on a high enough elevation, that the waters flowing out of it can actually cross the massive distance of 4500 kilometers south to the sea. So if for example the forest floor would be 450 meters up from the sea level, the average drop in altitude from there all the way to the southern sea would be only 1 cm for every 10 kilometers. That would mean all the lands the river flows through would be incredibly flat. Could a river even flow on such a flat ground, or would the water just gather there and form a swamp or lake or something? And no matter on how high altitude the forest itself is, the hills surrounding it from the west, north and east must be even higher, or the waters would simply flow to the northern sea. And this in turn comes with the problem that if the eastern hills (number 4) are too high, they would stop any rainclouds from reaching the forest (it is my understanding that even quite low hills can stop clouds and create a rain shadow?).
So the forest must be high enough from sea level to get the water flowing south through the continent, and the hills surrounding it high enough to force all that water to flow south, but still low enough for raincloud to reach the forest from the east.
As a side note, the mountains (number 1) are probably around between 3000 to 5000 meters tall, and if the hills next to them (number 2) are high enough that they will stop most of the rainclouds over the forest, I'm guessing that would make the hilly area between the mountains (1) and the forest (3) really dry. I'm still thinking of placing a few small kingdoms in those dry hills, so I'm wondering how people in those kingdoms could live - presumably trees wouldn't grow on the hills, and farming wouldn't be plausible, so would most of the citizens basically have to be sheep or goat herders? I'm assuming grasses and shrubs would still grow even on such a dry place, so the sheep and goats could eat them, and the people could live by eating dairy products and meat from their sheep and goats. And since firewood would presumably be in a really short supply, how would the people cook their food and heat their homes? Dried animal dung?
I really appreciate any advice you can give
Rivers usually don't follow a constant-slope profile; it tends to be more exponential. One 733km stretch on the lower Amazon, for example, drops a whopping 30 meters (it appears to be about two and a half centimeters per km in that stretch), while the upper reaches can literally drop dozens of meters per meter (waterfalls)! The same is true of most major rivers because the river will cut down into its bed until it reaches its lowest possbile elevation (the ocean). Rivers can only cut down if there is a sufficient altitude difference. Once the slope of the river goes pretty flat, it drops a lot of its heaver sediment load and starts cutting from side to side rather than down. It's this side-to-side cutting that causes meanders in the lower reaches of many rivers where the landscape is nearly flat due to early cutting and deposition.
The lower reaches of rivers do tend to be a bit swampy or marshy, but that's usually not a big impediment to enterprising people with sharp axes and pointy plows.
It doesn't take much in the way of elevation differences to make a river run away from what should be a closer run. A small ridge of resistant rock or even a sand bar deposited in times of higher water levels could make a river flow a long way around. It's more likely that the river will find the short path on geologic time scales, but if conditions change it may not have the opportunity to do so.
There are a number of possible explanations for a forest in that position. Glaciers on the high mountains, for example, could feed the river sources. Depending on the intended makeup of the forest, it could be drawing a lot of water from the those rivers. One important considersation is that plants put water into the air. Lots of water. That water condenses back into rain clouds and helps to grow more plants. A forest or grassland tends to be self-perpetuating to some extent.
On the other hand, there is an upper limit on how far water will travel from an ocean. Large continents will have large interior deserts, barring some effect that produces moisture in the interior like a large, shallow sea.
I scale on the map itself would help me in understanding what you're going for here.
My only comment is that with that small of an elevation change you would see a lot of meandering, but your rivers seem overly straight. In addition to the meandering, you get oxbow lakes from where the river has changed course during flood times. As waldronate mentions, even a sand bar (possibly deposited after a flood) can change the course of shallow river with a low elevation change.
Thanks for the great advice
I added two red lines to the map, the shorter one represents 1000 kilometers, and the longer one 5000 kilometers. So yes, the continent is pretty massive.
The point you made about there being an upper limit on how far water will travel from the ocean worries me. The great river which travel from the great northern forest all the way through the continent and into the southern sea (which is kind of like the Mediterranean) is one of the most important trade routes on the whole continent, so I can't really change the course of the river, even if the river turns out to be unrealistically long.
Basically all the lands west of the river (the area marked "A") are relatively dry anyway, they are grasslands where mongolian style tribal nomads herd their livestock, and the place looks basically like something between the American prairie and the Mongolian steppe. So even if the central part of the continent (the area marked "B") is really dry to the point of being a desert or very arid steppe, it kind of suits the general climate of the place and its cultures.
What I'm concerned about is whether or not that dry climate affects my precious river. Will the ground be so overly dry that it will hungrily absorb all the river's water, or will the river be unaffected by its dry surroundings. I admit it does feel a bit weird if a huge river as wide as the Mississippi will happily flow through a desert, but maybe it does happen. And if the river really can flow through an extreme arid steppe or even a desert, I'd assume the muddy riverbanks could support all kinds of plant life, so despite the dry surroundings plants, animals and people would presumably gather near the river since it would the only place for hundreds of kilometers around which could actually properly support life.
And if the unfortunate fact about there being a limit on how far water will travel from the ocean would also make my river impossible, how could I fix the situation? Would I need to ad a shallow interior sea or a massive lake to provide moisture (though where would that sea or lake get its water from?), or could rainclouds reach from the southern (Mediterranean type) sea to the north and bring rain to the central parts of the continent?
So as long as the Great river follows roughly the course it does now, everything's fine. And if the massive size of the continent makes it impossible for the river flow that way, I will just need to add more sources of moisture or whatever is needed to make the river plausible
At that scale, you probably wouldn't see much in the way of meandering. I recommend looking at maps of long rivers. List of rivers by length - Wikipedia, the free encyclopedia is a good place to start. I mention this because you can look at maps of them at different scales to get ideas of how your long river might look.
Is this an earth-sized planet (40000 km circumference)? If so, the north pole is going to go right on that little plain north of the great forest if that continent is indeed 10000 km in latitude extent. I've added some distance lines for reference to your map and attached the results. For a 40000km circumference world, rhe horizontal lines are the equator (0), 45 degree latitude, and 90 degrees latitude (pole). There would be undoubtedly be some projection effects on there that would make the lines not straight, but it's enough to get the idea. The location of your forest would be in the arctic ocean or in antarctica if it were here on earth. My math is suspect at the best of times, but I think I'm close on this one (40000 km total, half for a hemisphere, half again for equator to pole - should be 10000 km).
If the mountains in the north are a frozen wasteland, then the simplest explanation for the forest simply involves heat to melt ice. Admittedly, there usually isn't a lot of moisture in the really high latitudes because it mostly freezes out before it can get there. Weather pattern would be key here and you'd need a larger map to show other (if any) continents to get a good picture of those patterns. Of course, if this is the only continent, then there will be some really spectacular storms that could dump a whole lot of moisture on those mountains. Enough moisture and the glaciers will march down out of those high polar mountains and melt when they hit the volcanic province that is responsible for the large area that the forest sits in. It would play hell with the other cultures that you had in mind for the surrounding areas, but it would be very scenic.
What are the A and B point.
Originally Posted by waldronate
From the post where that map first appeared:
"Basically all the lands west of the river (the area marked "A") are relatively dry anyway, they are grasslands where mongolian style tribal nomads herd their livestock, and the place looks basically like something between the American prairie and the Mongolian steppe. So even if the central part of the continent (the area marked "B") is really dry to the point of being a desert or very arid steppe, it kind of suits the general climate of the place and its cultures."
Now that I think about it, I think this planet would probably end up quite a bit bigger than Earth. There's another continent of roughly equal size to the east (in fact if the map was a bit wider we could see part of the western coast of that Easter continent), and I've always imagined that the Northernmost tip of this continent (the part just above the Great forest) would look pretty much like the Nordic Lapland, which I think is something like 67-70 degrees latitude. Lapland does get very much snow every winter, but during the summer months it does completely thaw.
Originally Posted by waldronate
So if that northern tip of the continent really was just 70 degrees latitude, and therefore the actual north pole would be quite a bit farther north, the planet would probably end up quite massive. Though I'm really not sure exactly how massive, since Math isn't really my strongest point :p
It should be a little more than 1.5 times the circumference of earth if the 90 degree line I drew on the map should really be about the 60 degree line (90/60 = 1.5). Then again, math isn't my thing, either...