River help

[lokiie1984]

On the map I'm having made, i need a river to move and flow like the amazon does. Twisting and winding and tons of little feeder rivers forming from the massive amounts of rain fall. What i need to figure out is what kind of changing to the land in that area i need for it to work the way i want.

Amazon.jpg

I know its wrong in there to some degree, the feeder rivers would flow into the main river heading east rather then north and south but its a good way to get the jist of what I'm looking for. Personally i don't understand how the amazon works, and i doubt i ever will. All i know is that it has a lot of rainfall to feed the river and other smaller rivers. And i assume the trees have something to do with why the river does its "snaking" thing.

Now though for my map is there anything to the land that needs to happen for that to work logically? (It is a world map and set fairly high up so if need be i wouldn't need to show the feeder rivers at all.) Should the mountains be taller?

Thanks

[Schyzm]

OK, so the amazon basin is essentially one huge bowl. If you think about rain falling in a bowl, it always travels the nearest, steepest path to the middle.

In terms of the reasons rivers give themselves a serpentine shape is that they are in a long, mostly flat area, and they carry a lot of particulate matter (silt, salt, dirt, etc). the fastest water carries more of it, and, like a merry-go-round, it travels on the outside of curves. this carves curves wider - meanwhile the slow water can't carry as much of the particulate matter, and travels on the inside of the curve - and since it can't carry as much, it dumps the excess. the shape evolves because the water still tries to go down hill the fastest way possible.

So in terms of your map:

1) tear out the rivers and lakes you already have.
2) map your elevations in depth first. (pun intended!).
3) give yourself an extra layer and map out the fastest points to the lowest common grounds.
4) draw the rivers in. Remember that rivers make a Y shape, rather than a T.

if all else fails, there's a thread about rivers in the resources section of the forum that's worth reading.

[lokiie1984]

So if i understood that right, the outer edges of the forest, where the feeder rivers are, would be a slightly higher elevation then the large winding river.

As for doing the thing in gimp or what ever, i don't have to worry about that as I'm paying a guy to do the map. I just wanted to make sure the river in itself was possible there. That it didn't break any river rules. Which it sounds like its fine. I will just have him draw try and draw it like you described, if its even needed. As a high up aerial view I'm not sure if it would need to be shown that way anyway.

Now my second question, one of my other rivers flows south and when it hits a desert (large sand dune type desert) it goes under the sand and pops back up in the forest. Would they logically do that? I figure it could hit an underground cave system.

[Schyzm]

well, the water table could, conceivably, sink under it... but unless you had another elevation change and there was a low point, the river wouldn't really just pop back out. Instead, I'd recommend the river go through the desert - plenty of deserts in the real world have rivers that pass through them without additional rainfall coming in, and the spring flood cycles have been known to power the agriculture of major civilizations (egypt, for one).

[lokiie1984]

It needs to go under the sand. Or not really be there, the reason is the desert is one of the main obstacles keeping people from going west. There isn't enough easily accessible water to cross it. Which is why i wanted it to go underground. But for the matter it doesn't really have to pop back up. It can just hit underground caves until it finds the ocean.

I have a few creatures that live in those caves too, so i think that would work. I need to figure out how to use Wilbur with gimp and get some more rivers into the sample map i made. Mostly just for the artist to use as references. But its also neat to play with.

[Chashio]

There are underground river systems in deserts. I doubt they would involve caves unless the desert was somewhat rocky/mountainous (of the right kind of rock), but I'm not actually sure on that. You might have your subterranean river sink into the sands of the desert, and as it hits higher bedrock near your forest it could pool into small lakes and then turn back into rivers on the surface that flow through your forests, while also eating away the bedrock in places underneath to create a cave system under the forest... they'd be filled with water, though, unless your creatures are sentient and crafty enough to seal off the cracks or the river takes a deeper path leaving the higher caves dry. You might do a search on subterranean rivers in deserts and see what options are already there. You might also like to investigate blue holes. Find out what types of rock are most likely for your scenario and see if you can work those in to suit your needs.

There's also the springs that well up in the mid-east of Australia, formed by an inland sea which left behind a layer of mud to seal off the porous sandstone underneath. Rainwater seeps through the cracks of the mud into the stone and then keeps that water from evaporating. Where the mud layer is broken the water pools up on the surface. Not quite what you want though, I think.

[waldronate]

Karst Hydrology - river, system
Karst - Wikipedia, the free encyclopedia

I don't think that the Karst subterranean rivers will be stable over hundreds of thousands of years because the river will dissolve the rock over time, especially if the river is a large one. But a small catastrophe could have triggered a number of sinkholes and perhaps a small rise in the bottom edge of the river. This sort of scenario could allow for the river to disappear at its upper end, the reappear at the foot of a large limestone cliff. If the desert is at the top of the cliff, then the sands could occasioanlly cascade from the top of the cliff as well.

And there is a whole host of magical reasons for a disappearing / reappearing river, but all of them generally require some sort of long-term energy input:

A god / wizard / other decided that the fertile land that is now desert offended them for some reason and dropped a portal across the river to bypass the land, drying it up. In this case, if the portal passes things other than water, it allows for fast travel across the affected area. Sounds like this is exactly the opposite of what you want.

Similar concept, but the portal either runs through a massive time dilation barrier (in effect, it takes thousands of years for the river to flow through that section) or an energy barrier (huge turbulence or temperature shreds anything trying to pass the barrier).

The river runs through a tunnel specifically created for the river. This tunnel was created and is maintained by whatever agency deemed it necessary. An an example, an aquatic race living in the river had to take drastic action to construct a roof over their river as the desert sands began to sweep in to prevent apocalyptic destruction of their homes. Another example would be strife between two god-type beings that resulted in raised land and destruction across the disappeared area. One of the two (or a third agency) protected the river to preserve their favored agents downstream, resulting in it holding its position as the land was churned and rose above the river. This scenario results in the river being a special gift to the downstream agents (and their successor groups, if any).

[jbgibson]

For your disappearing river, how about a geological sequence of flat land w/ curvy river, uplift to become plateau, steep canyons cut during the uplift, then earthquakes somewhat crumble the canyon, climate dries up some, dunes drift over the former canyon lands. Result being a sea of dunes (and rocky outcrops if you like) with a nice roomy former river course beneath.

The sand might at first tend to filter down and clog the cracks between boulders - just assume the clogged bits could get washed back clear by occasional high flow. That could be a silly assumption, but who's going to be down there inspecting your geology? :-)

[lokiie1984]

For your disappearing river, how about a geological sequence of flat land w/ curvy river, uplift to become plateau, steep canyons cut during the uplift, then earthquakes somewhat crumble the canyon, climate dries up some, dunes drift over the former canyon lands. Result being a sea of dunes (and rocky outcrops if you like) with a nice roomy former river course beneath.

The sand might at first tend to filter down and clog the cracks between boulders - just assume the clogged bits could get washed back clear by occasional high flow. That could be a silly assumption, but who's going to be down there inspecting your geology? :-)

I like that idea, it could easily be shown on the map too with the rocky outcrop.

The reason i asked is because i don't want readers to look at the map and then question my rivers. (I'm sure most readers wouldn't care or notice.) But with the rocky outcrop it covers my ass just in case lol River hits the outcrop and goes poof.