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Thread: Lakes with multiple outflows?

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    Guild Journeyer Thurlor's Avatar
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    Question Lakes with multiple outflows?

    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.

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    Community Leader Facebook Connected Steel General's Avatar
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    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.
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    Community Leader Facebook Connected Ascension's Avatar
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    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.
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    Guild Journeyer Thurlor's Avatar
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    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.

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    Guild Artisan rdanhenry's Avatar
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    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.

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    Software Dev/Rep Redrobes's Avatar
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    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.

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    Guild Journeyer Thurlor's Avatar
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    It seems that every example I have found is artificial in some way. Ah well. So be it.

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    Guild Apprentice Hungry Donner's Avatar
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    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.

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    Quote Originally Posted by Hungry Donner View Post
    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.
    Fluvial islands are also unstable in the long term. One channel wins, or the island gets eroded away.

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    Guild Apprentice Hungry Donner's Avatar
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    Quote Originally Posted by Hai-Etlik View Post
    Fluvial islands are also unstable in the long term. One channel wins, or the island gets eroded away.
    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.

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