Reply With QuoteI understand all that.
But in my mind, something that I had (for awhile) considered 'impossible' is merely implausible... and that's a big difference. Especially when creating fantasy maps.
Yes there are a few. See https://en.wikipedia.org/wiki/Bifurcation_%28river%29 and also Isa Lake - Wikipedia, the free encyclopedia. But note that in all of the cases they are on geologically unstable places. Specifically for the Teton Two Ocean Pass its on the North America Continental Divide and the Isa is at Yellowstone. These places will only exist temporarily and in a few hundred years or perhaps a little more but trifling geologically, one side will dominate the flow. There are more that normally only flow in one route but during floods will cause the flow to exceed the capacity of one side and will then have two paths to different places. It is a certainty that at the very edge of the catchment basin where it meets its neighboring catchment basin then a drop of water is critically unstable in its route to the sea. There would exist many places where the flow is a merest trickle and then bifurcates but the more considerable the flow of water the harder it would become to show the bifurcation. A larger flow would erode one side faster than a trickle over the flat ground on the edge of catchments.
I understand all that.
But in my mind, something that I had (for awhile) considered 'impossible' is merely implausible... and that's a big difference. Especially when creating fantasy maps.
In fantasy, physics need not apply. A DM I once knew decided that the big mountain in the center of the island should disappear, leaving a big hole. The large river that had flowed from the mountain to the sea now served as a channel for the sea to flow back into the big hole. Implausible, but possible. And certainly not stable. Ever since the big hole appeared just south of the Sea of Fallen Stars in the Forgotten Realms, I've been waiting for some enterprising gnomes to dig a canal from the sea to the hole and set up a few waterwheels on it. The unintended erosional consequences and migrations due to flooding would be hilarious!
So, pretty much this: Qattara Depression Project - Wikipedia, the free encyclopediaOriginally Posted by waldronate
Or the one from the Gulf of Aqaba to the Dead Sea, or the one from the Gulf of California to the Salton depression, or the one from the Red Sea into the Afar depression. It's a popular topic. It's also a major ecological disaster for the ever so fragile ecosystems (except for the Salton depression, which has already had that particular disaster). But the Forgotten Realms one is particularly interesting because the hole is very deep and the distance not too far. When the gnomes put their giant hamster wheel-powered excavators to work on a basic canal, accidental erosion could VERY quickly turn it into a miles-wide waterfall unless there is a very solid ridge in the way. It's mostly plains with no particular hills in the way...
I didn't know that about Lake Baikal. Thanks for pointing that out. I should have caught myself with the obviously inconsistent statement about the Great Lakes. I've been looking at fractals lately and river systems are sort of like that, especially as you look at them in closer and closer detail.
Last edited by Trismegistus; 06-15-2014 at 01:19 PM.
Crosslinking another thread:
http://www.cartographersguild.com/sh...433#post258433
Bryan Ray, visual effects artist
http://www.bryanray.name
Redrobes pointed me to this thread. I have just finished a PhD in Hydrology so i might be of some help with questions. I am not a geomorphology or classification specialist (which looking through this thread is mostly what is being discussed) but i know more than most.
" The delta area is probably too large with regard to the river's length. I justify this by saying that the tectonic rising of the subcontinent of Pytharnia has forced the great discharge of the Shadew River to make new channels over many tens of thousands of years, so the river cuts down as the earth rises up. The Shadmouth, or mouth where the Shadew River enters the delta is easily over two kilometers wide. The nation of Bangladesh is striped with the braids of the Ganges River, however, it is relatively flat."
noticed this. Deltas are generated by deposition of sediment. The river loses energy as it reaches the sea (moving water hitting water moving in a different direction) so it dumps its load of sediment. This creates lots of extra soil that the river still has to cut through to reach the sea, so you get lots of little channels. Delta size is a function of how much sediment it is carrying rather than its length or even the amount of water (although a longer river with more water will generally have the ability to carry more sediment).
If you have a large delta a couple of things should be true. First, the river should look brown, as its carrying loads of soil. Secondly that soil needs to be eroding from somewhere. Eroded soil can come from lots of places. It could be that the river has eroded deep gorges, or that hard seasonal rainfall just washes the top soil off the great plain each year. A river with a lot of soil in it will typically be lower energy, move slowly and meander a lot, but there might be exceptions to this (the Nile doesn't meander excessively for instance in its lower reaches).
hope this helps.
I have also studied geography as an undergraduate and in general know stuff about the earths features.
Some quick thoughts:
River bifurcation is probably something you should only use if you're really aware of how weird it is and yes if it's everywhere on you map you'd better have a good explanation for it. However I don't think it needs to be forbidden completely since at least one real world example had a real influence on human civilization.
The Amu Darya used to drain into both the Aral and the Caspian - the latter via a large distributary known as the Uzboy
( http://everything.explained.today/Uzboy_River/ ) which flowed from at least the 5BCE to the 18th Century CE. More importantly the Uzboy was navigable for most of its history so it was possible to ship goods from the Aral to the Caspian by water - just think of the world-building implications of that.
The Uzboy may also have been an early victim of the same hydrological mismanagement that has killed the Aral Sea rather than geology but I might be misunderstanding that.
On the subject of endorheic basins I think a lot depends on the size and position of your continents. A huge Pangaea like continent with lots of mountains and rainshadow deserts at the heart is going to have many watersheds where water simply can't reach the sea and either ends up drying up in the desert or flowing into an endorheic lake because gravity drew them inland rather than to the sea. A small continent less so but even Australia has Lake Eyre and the rivers that feed it https://en.wikipedia.org/wiki/Lake_E..._basin_map.png so it's possible, just less likely than on a huge continent.
Becka
This is all great stuff. While a lot of this seems like common sense, it's easy to forget, and thus quite useful. I would add to this that many rivers start from high mountain ranges from snow or glacier melt, and in those cases you'll sometimes see lots of small streams that come together into valleys as they descend the mountain. If the map contains that kind of detail, that is.
