View Full Version : Lakes with multiple outflows?

05-15-2011, 06:53 AM
Hello all,

I've done a quick google search that hasn't really helped me, probably as I'm not using the right terminology. Anyways, as I'm pretty sure that they can exist, I'm wondering how common/rare are lakes with two or more outflows.

Steel General
05-15-2011, 09:37 AM
To the best of my knowledge (and I'm no expert by any means), they are rare. Eventually the water level will lower enough that only one outlet will remain viable.

05-15-2011, 10:10 AM
The only realistic way for a lake to have more than one out-flowing river is for those rivers to be man made canals. Even if two rivers flow out at the exact same height, exact same slope, and over the exact same rock this will only be temporary. One happy accident and a rock cracks and allows a tiny bit more water to flow through it and the other river will dry up. If you'd like to experiment then dig up some dirt and make a little hill, dig out the center to form a bowl and pour some water in. You will see some of the water flow over the top but you might also get one of the sides of the hill to collapse. Larger lakes don't run as fast as the little example but they act similarly nonetheless. Plus, it's fun to just play in the dirt from time to time. :)

05-16-2011, 01:59 AM
Further 'research' on my behalf has led me to having a close look at maps of Norway. If I'm reading the maps correctly then there are numerous 'splitting rivers' as well as a few lakes with at least two outlets. I'm having a bit of trouble confirming some of the names with Google Maps and finding the right lake, but apparently one exists that has two rivers exiting it. One leads to the atlantic and the other to the sea near Sweden. Basically splits the country. I think the main thing required is lots of glacial action throughout the region/world's history.

05-16-2011, 08:58 PM
Perhaps you found Lesjaskogsvatnet (http://en.wikipedia.org/wiki/Lesjaskogsvatnet) - quoting Wikipedia: "The lake was dammed to serve the Lesja Iron Works in the 1660s and now has two outlets." This is an artificial situation.

05-16-2011, 10:28 PM
You can get multiple outlets if its a temporary measure like damming or if there is a sudden rainfall causing temporary flooding. You can get it to some extent with glacial action but it would have to be pretty active or perhaps seasonal whereby, for example, one river is dammed through being iced up for only parts of the year. Otherwise, in general and in the longer term, one river will always win since its an obvious note that you had two rivers with good carrying capacity and it was steady flow then the water in the lake would fall to the lowest. Where they are equal, one would silt up before the other and then the winner takes both flows thus increasing the erosion on that flow and causing sediment build up on the other. So a man made or changing environment I could believe but I don't think it can happen in a steady state long term deal.

05-17-2011, 02:07 AM
It seems that every example I have found is artificial in some way. Ah well. So be it.

Hungry Donner
05-17-2011, 07:19 PM
You can get the appearance of a splits if the two rivers rejoin further downstream; I can't think of any examples with lakes but this isn't uncommon with rivers: Bananal Island in the Amazon immediately springs to mind.

05-17-2011, 10:59 PM

Fluvial islands are also unstable in the long term. One channel wins, or the island gets eroded away.

Hungry Donner
05-18-2011, 08:53 PM
That's fair, although you can set up a situation where fluvial islands are also typical so even if one erodes you're likely to get a new one soon enough. This really does work better for rivers than lakes though, I suspect lakes that border such regions tend to have substantial wetlands around them.

05-20-2011, 08:51 PM
The exception to the rules may be Lake of Two Mountains (http://en.wikipedia.org/wiki/Lake_of_Two_Mountains) in Canada. It has one major inflow the Ottawa river and four outflow.

05-21-2011, 01:51 PM
The Lake of Two Mountains is part of a river delta (an area of exceptions, as river splitting is normal - but note that individual riverways are temporary, deltas are rapidly shifting areas of water flow), and it also is part of an artificially regulated system, although I haven't been able to find any indication that the lake itself is artificial. It is a shallow lake and could perhaps arguably be described as a wide section of river. Looking at it on Google Maps, it appears that all these different outflows join up again rather quickly, meaning that what one actually has is a set of islands breaking up the outflow.

05-21-2011, 07:51 PM
Not worth debating really, folks are always trying to justify their backwards rivers and octopus lakes. We offer advice, they get defensive, shrug...way of the world.

Hungry Donner
05-25-2011, 09:23 PM
Especially the internet :D

06-07-2011, 06:35 AM
So, this is a very interesting discussion for me. Weird river layout is a pretty embedded 'trope' (if you will) in the game world I'm designing for: Earthdawn. Specifically, the Serpent River, which was generalized from 2 separate river networks (which, yup, the creators kinda smudged the terrain in their heads and threw a lake there). Here's a pic of the official game map. Notice Lake Ban in the SE area near the sea.


One outlet flows to the Aras Sea (the Caspian), the other outlet flows to the Mist Swamps, which are lowland swamps on the edge of Death's Sea, a large expanse of Lava around the Crimean peninsula, which evaporates the outflow into weather patterns. In the fiction, the entire general course of the Serpent River is described as navigable, and the lizardmen T'skrang houses ply fire-engine wheeled Riverboats along most of it.

I'm pretty temped to just make it "a Dragon's did it" call, as they are the standard meta-manipulators in the setting, and the T'skrang mythology describes the River as a Dragon herself....

But I'd like any other input....

06-07-2011, 12:29 PM
You could call the Coll (sp?) River a canal—an artificial channel designed to facilitate shipping from the Aras to the rest of the river system. It would require continuous maintenance, probably at both outflows, to maintain the stability of the system. In addition, adding the canal would likely have significantly altered the behavior of the lake. If the second channel was naturally cut by overflow during flood season, then the presence of the canal would mean that the impact of floods is lessened. In the short term, that means that lots of usable land would have been opened up around the shores. In the long term, the farmland surrounding the lake would gradually lose its fertility, since it is no longer receiving deposits of silt during the floods.

06-10-2011, 01:27 AM
Hey Bryan, thanks for that. I think that the T'skrang houses might be savvy enough to technologically handle that. They're the only culture in the setting with what we would know as "modern" technology (steam works), but it's kept very hush-hush (even the Captain of a steamboat doesn't know how the engine _works_... that's what the Engineers Cult is there for).

T'krang also build their "Cities" in the middle of lakes/rivers, from the bottom up, so they're adept at magically aided underwater construction, etc.

Thanks for the ideas!

06-10-2011, 03:45 AM
Wouldn't it just be easier to say that the connector between lakes Ban and Puros is the artificial one? It's short, relatively straight, and looks like it wouldn't naturally be there. A few smallish streams to operate some locks on that river and all's well; cutting through a few hills and the water would naturally flow, but it would be tricky to maintain a long-term balance (see the ongoing battle to keep the Mississippi from hopping into the Atchafalaya's bed here in the US).

Of course, if the water to the lower right isn't particularly salty, then the lava in the lower left might be a semi-recent collapse, leaving it below sea level. In that case, the lower parts of the Coil river might well be running backwards into Lake Ban before joining the outflow to Lake Puros on the way to Death's Sea. Depending on how recently the collpase occurred and how salty the water is, all kinds of things might be getting poisoned by salt along the lower river reaches, making for a pretty good amount of nasty salt marsh-type vegetation. Just the sort of thing that estuarine lizardmen might prefer, in fact.

06-10-2011, 09:45 PM
I've also been considering (Seasonal) backflow from the Aras. The IRL terrain is weird in that area. The Volga (the base of the greater nothern Serpent, IRL) does exit along the "southern Coil" as shown on the ED map, and the "northern Coil" is actually part of the river system that flows down towards Death's Sea/Sea of Azov. I like the interesting environment that idea sets up. In my Map, the Aras(Aral) Sea surface is @ a higher elevation than the laval field (by about 50 meters) so that might be interesting.

As you can see from a recent render of mine, I had to "hop" the the course of the northern Serpent/Volga (over a set of hills/ridges) as in came in towards Lake Ban (the "Z" turns above the word Lake):

Thanks again!

06-11-2011, 06:03 PM
If you take out Volgograd with a huge force (large enough to make a hole 105km from end to end that gets filled to make Lake Ban) then it would be enough to bridge the Volga River over to the Don and thence into the Black Sea. There is a bit of a disconnect in altitudes with the given shorelines, but it's easy to invoke a bit of altitude adjustment with a disaster of that magnitude.