Question for the River Police (TM)

[Phlimm]

I have seen on several maps, and have on my current world map, rivers that flow for a while, widen out into a small lake and then narrow back down to a river again at the far end to continue on to the ocean. Is this an accurate construct?

Thanks!

[jbgibson]

Yes. Anything from a mere wide spot in the river up to Lake Michigan is perfectly plausible midstream.

And if one needs a largeish island partway down a river, portraying it as an island in such a lake rather than a split watercourse is better.

[Phlimm]

So what is the difference between that and what I have seen as critiques that lakes cannot drain to two rivers?

[s0meguy]

They can, but they come together again, thus creating an island in the river. Draining into 2 separate rivers doesn't happen because rivers erode and eventually one of the rivers erode deep enough to lower the level of the water, thus taking away the other river's supply of water. That's my understanding of why it is impossible anyway.

[Phlimm]

So then if I understand it, this "drawing" is correct then? (pardon the MS Paint, I just want to understand the concept):

River.JPG

[s0meguy]

The upper is the right one indeed.

More than one river can enter the lake though, but there is only one outgoing river.

[priggs]

I think if you remember these, you'll be OK:

1. Lakes form for a reason. Something blocks or delays the flow of water so that it backs up. Lakes are just a backed-up river. So, for example, things could be a dam of human or beaver origin, a low-lying area that has to fill up until the water reaches a height to flow again (a valley), a depression caused by ancient ice sheets (Great Lakes), etc.

2. Water always follows the path of least resistance. That's why a lake doesn't have two outlets. The backed-up water is looking for the easiest way to escape, and once found, all the water will follow. If a second outlet were to form, that would mean it's an easier path of least resistance, and all the water will follow that path.

3. Natural lakes most often have multiple rivers running into them because of number 1. above, because something is pushing the water down into that depression and limiting the rivers from proceeding down a different path, such as a mountain, hill, etc. Reservoirs are more likely to have a single large inflow river that has been dammed to create the lake.

4. Serpentine lakes flowing over a flat area can form oxbow lakes where the water has gone out too far and the river has changed to a more direct route, cutting off the oxbow.