River Placement Questions - Where can they begin?

[Zedfelos]

Hello!

As the title says, I'm looking for advice on where my rivers should begin. I'm familiar with the age-old mantra "Rivers never split", but what about "Where do they begin"?

Now, I know most rivers begin in the hills and mountains of the world. However, with the exception of springs, where else can they originate? I have a first-time map that I'm building up, and my rivers look strange just coming out of the mountains all the time. On the other hand, I think they might look even more strange just popping up in the middle of grasslands. I suppose some could originate out of certain lakes, perhaps?

I want to see what my options are. Any advice you could all bring to the table would be most appreciated.

[Gamerprinter]

Anywhere there's higher elevation is going to be the source of your rivers. Water flows downhill. So in mountainous areas, the mountains is the source, but in relatively flat terrain, wherever the higher elevations - hills, etc. creeks form join wider creeks, form small rivers, join larger river, enter lakes, or eventually reaching the sea. Where on your map is the highest elevation area - start your rivers there, or even off page, where it's presumably higher elevation, and have the river pass through your mapped area.

GP

[rdanhenry]

The real practical question is "Where does enough water start flowing together to show on this scale of map?" Because you're not going to want to map where every single drop of snowmelt starts its journey all the way to the sea. For every mapped river, there are all sorts of streams and rivulets and brooks and trickles that don't show. If you don't want to map anything that can be crossed by wading unless there's a flood, you could be into the lowlands before you need to start showing rivers. While some rivers begin in springs, others come out of glaciers, others are the run off of precipitation, either freshly-fallen or dumped as snow and slowly melting. Big rivers may trace back to all three. Lakes are not in themselves sources of rivers, but areas where water flows in and then out again. Where is the lake getting its water? Probably rivers or streams. Which is not to say that a mountain lake might not be the first place that the water shows on the map.

Of course, in fantasy mapping, there are additional sources of water possible. But wherever the water comes from, it's going to be at a high point compared to all the water downstream.

Anyway, my point is that you have decisions to make about how much river you want to show, which is going to affect where you want to start them. Look at a bunch of different continental maps. You should be able to find a good deal of variety in how much they show of the river systems. In terms of your maps, there's a good deal of wiggle room in how you show water flow.

[waldronate]

A river/stream/spring will start/occur any place where the water table is higher than the landscape. Water will continue to flow downhill as long as the water table is above the landscape, the water will flow downhill. There are lots of apparent exceptions, but those are usually related to changes in ground permeability (which affects the water table) more than any actual exceptions.

The most common places for the water table to be high are where there's lots of water, such as below snow caps on mountains. Mountains tend to accumulate more rainfall than plains, and rivers will often start there. However, if all of the water for a river were required to come from high sources, there would be very few rivers! What normally happens is that water falls all over land and soaks into the soil. That water forms the water table and tries to find a uniform level. When it impact the surface is when it becomes visible surface water. It's all of that water stored in the water table that makes rivers get larger as they flow along.

Apparently weird rivers happen a lot. A fairly common problem is disappearing rivers. Rivers flow along, collecting tributaries, and growing nicely. Then they hit a sand area, like an old dune field. The river shrinks dramatically, sometimes disappearing entirely. It may suddenly appear miles away from the sand. A river in karst terrain can just fall into a cave and be gone. It may appear later or it may not.

[Zedfelos]

Thanks for the replies, everyone!

So, what I'm getting is that as long as there is enough water accumulating in an area (for potentially multiple reasons) and that there is a place downhill for that water to go, a river can form. I especially like what you said about mapped rivers vs. unmapped rivers, rdanhenry. That really helps me to conceptualize what I'm mapping here.

Let's see what I can make of this!

[Bioluminescence]

You have many excellent examples and descriptions above, but I'd like to add a personal story that might help you or others reading this.

When I was a kid, our school took us to visit the source of a river. This particular source was, as you might imagine, up in the hills in an incredibly wet area. It was misty, and the ground was incredibly spongy due to it being comprised mostly of peat and moss. It's useful to think about this area as being like a sponge - as if you've placed a sponge on a hard surface that lies on a slight angle. The rain and dew would deposit water in this area quite frequently, saturating the ground (the sponge) until it could hold no more water - at which point, the water started to spill out at the easiest point - the lowest point. Much like when a sponge is supersaturated and a rivulet of water starts to run off the bottom of the sponge.

Of course, there wasn't a single, obvious, absolutely definite, spot where you could say that "Here is river" and "Here is just really sodden dirt with puddles" - but that area as a whole was the general source, or highest spot, of the river that would eventually gather water from lots of other 'sponges' and runoff.

Having such a wet location (with all the fog/mist, dew, and rain in the hills in a temperate location), and the ground being so spongy, meant that the source was pretty reliable. The river ran all years. Unlike if the rain were to hit solid rock (with nothing to act as a 'capacitor') only one season a year, causing flash floods and wadis.

[JoshStolarz]

Thanks for the replies, everyone!

So, what I'm getting is that as long as there is enough water accumulating in an area (for potentially multiple reasons) and that there is a place downhill for that water to go, a river can form. I especially like what you said about mapped rivers vs. unmapped rivers, rdanhenry. That really helps me to conceptualize what I'm mapping here.

Let's see what I can make of this!

There's already been some great answers to the question, but I will throw in a personal example regarding the idea of mapped vs. unmapped rivers. Here in Oregon where I live, there is no shortage of mountains and it rains all winter. Needless to say there are quite a few large rivers running through the state. But, I have seen several maps that actually do map all the tiny streams that flow down from the mountains and there are so many of them you can pretty much see the form of all the individual mountains. Basically, anywhere two mountains meet or there's a low point, there's a strong possibility there will be at least a seasonal stream that forms.

- Josh