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Comment by dsmithatx | Hacker News Reader

I immediately thought of Devil's Kettle Falls reading this. I had to Google it and found that 4 months ago scientist have decided it flows back into itself. They have a plan to put a large amount of dye in during low water and see where it reconnects.

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Ah the circular river. Very rare but useful to extract energy from.

Have people done this?

I'm quite certain the GP was a joke.

Only badly worded. The missing water flows back into the visible river somewhere downstream, not upstream.

Yes: http://www.mcescher.com/gallery/recognition-success/waterfal...

Does extracting energy from a circular river affect it's ability to continue being a circular river?

Just a river with an island, in a topological sense.

Well an underground volcano or something could inject energy into the system so you are probably ok, thermodynamically.

most rivers are circular - just that the upstream water flow is invisible, by virtue of being in water vapor form.

That's very deep. I'm impressed. Sincerely.

But is it true? The flow rate of the Mississippi (I got ~500 cubic km/year) is about 0.025 Great Lakes (20,000 cubic km combined) per year.

The oceans are 1.37 billion cubic km.

Yes, it's true. Most of the water that flows from the Mississippi into the Gulf of Mexico comes from rain. And most of that rain comes from ocean evaporation. Sure, there's some input from aquifers, and some recharging of aquifers. And there's evaporation from the Mississippi, its tributaries, and all of the associated lakes, wetlands, and so forth.

But the fact remains that the Mississippi is part of the global water cycle. And cycles are circles.

I sort of assumed that knowledge of the water cycle was a given.

But how fast does the water have to cycle for a named river to be part of a circle? Does once every 10 million years do it?

That's a fair point :)

Not circular, just rejoins downstream after the split.

Indeed. This article describes things further:

http://www.startribune.com/scientists-think-they-ve-solved-t...

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