Mountains -> Swamp -> River Question

[seycyrus]

Greetings,

I've made and been using the attached player map for my group and realize I might have created an unrealistic topology. I have lurked long enough to have picked up on some of the rules of rivers, but realize I might have made a transgression.

In the map, the main river flows from North to South. My question is about mountain area in the southeast (fenced by the rivers). The greenish area (yes, I know there many greenish areas) around those mountains (fenced in by the rivers) is meant to be swamps or marshes. Is this realistic? Does this ever occur in the natural world? Does water ever flow off of mountains via a bunch of small streams etc. into a flat swamp area and THEN drain into a larger river?

Thanks for your help!

Oh yeah, other criticisms of the map are welcome as well. Yes, the castle is not to scale

[Chick]

...Does this ever occur in the natural world? Does water ever flow off of mountains via a bunch of small streams etc. into a flat swamp area and THEN drain into a larger river?

Highly unlikely. Terrain around mountains is almost always sloped from the mountains down to the centers of the valleys, so to have a low marshy area around the base of the mountain would be extremely unusual.

You can, of course, invent some reason why it's that way, but I doubt you can find many such places in real locations.

[jbgibson]

Chick's statement is an excellent generality. At the same time, I can think of a bunch of places in the Colorado Rockies where a river valley - an extremely steep-sided one - has a marsh in its very flat bottom. That's a lot more localized than what you are showing - say hundreds of yards to a couple of miles across vs your apparent tens or a hundred miles of marsh. But I can imagine a couple of geological processes that would generate direct steep-to-flat transition.

You depict sharp, rugged mountains, so the range is young, OR there has been general uplift and they are 'young again'. Erosion is active, maybe there's been glacial action in the last umpteen thousand years. If uplift was uneven, and the original area that's now a river valley was a bit of a closed basin, it would for a while have collected a lake, which sediment could have filled in till it was essentially a lake of dirt, at which point more uplift, or erosion of the 'lip' of the basin could have increased outflow till you have the present river across flat bottomland.

At various scales, this happens all through mountain ranges - you'll see modest to even extensive flatlands right among peaks.

I would probably buy your situation better if the river meandered *through* the marsh, not skirting its edge. It wouldn't have to disappear into the marsh as a distinct stream - though that can happen.

Google "Alpine lake" and look at some images. Two main shapes of such valleys - v-shaped clefts that are just continuations of visible steep slopes, and u-shaped valleys scraped out by glaciers. Imagine any of the u-shaped valleys as they silt up with eroded mountainside - many will fill in to utter flatness like the ocean end of a mature river system - so for a space those young jagged rivers may loop and oxbow... and marsh.

One reason you'll see less such marshlands in recent times is that humans tend to drain or fill in such land to make "better use" of it. If you're in a ruggedly mountainous area already, there's precious little arable land, so a hundred or three years ago the locals would have chosen grazing or barley over wetlands and bird habitat -- all this if it's well-peopled. How well populated is the area of your map? For that matter just what area does it cover?

[Gamerprinter]

Alakai swamp near the top of an extinct volcano on the Hawaiian island of Kuau'i is considered a mountain wet forest and is almost a mile up in elevation on an island. It is one of the wettest spots on Earth with over 750 inches of rain a year. The tropical trees are stunted (no more than 10 feet high, though many are essentially natural bonsai trees), and it is overcast most of the time, when its not raining.

[Chick]

Yes, you can have a low spot that accumulates water at any elevation, but that was not the question. There are exceptions to most everything in very special unusual circumstances, including the caldera of an extinct volcano, but is it common, normal, usual, typical ... no.

[woekan]

I love the way your mountains look!

On your question. Wikipedia "Swamps are characterized by slow-moving to stagnant water." They exist around large rivers and on the edges of lakes. The swamps usually are around flat area's of land. They wouldnt be so close to mountains because of elevetaions unless there are some really unusual circumstances.

[Gamerprinter]

@chick - I agree, and my point was an "exception", however Alakai isn't in the caldera, rather away from the caldera to one side. Mount Wai'ale'ale, the volcano in question has a dome, but the upper portion is very flat and only drops in elevation several miles from the caldera dropping into the sea or the lower beach areas. It is certainly unsually topography.

[seycyrus]

...where a river valley - an extremely steep-sided one - has a marsh in its very flat bottom. That's a lot more localized than what you are showing - say hundreds of yards to a couple of miles across vs your apparent tens or a hundred miles of marsh.

Thank you for your reply. This map is meant to be a players map, and by that I mean, that it is supposed to convey the generally feeling or gist of the terrain. The scale for the entire map is about 30 miles from eat to west, so the swamps occupy land on the order of miles instead of tens+ of miles.

What elements of the map convey the sense of a greater distance than what I intended?

One reason you'll see less such marshlands in recent times is that humans tend to drain or fill in such land to make "better use" of it. ...-- all this if it's well-peopled. How well populated is the area of your map? For that matter just what area does it cover?

The castle depicted is an outpost protecting a frontier. Forgive me for assuming, but think "Keep on the Borderlands" type setting. The depicted are is about 30 miles x 30 miles. it is a fantasy setting, and thus things could have shifted in the previous 10k years or so.

Thank you for your reply!

[seycyrus]

I love the way your mountains look!

Thanks! The map was made using CC3. I was trying to get the feeling of "being there" that some of the maps in this community convey. I liked the way the mountains looked so much, that it seems I put down some where I shouldn't have!

[seycyrus]

Highly unlikely. ...

Thanks for your reply!

If I might take some more of your time. With the limitation of keeping some sort of "swamp" in the area, is there anything that might make it more believable? Maybe remove the mountains in the area fenced in by the rivers or something like that? Put in a small lake instead of the smaller river?