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Author Topic: Do rivers have a slope?  (Read 3961 times)

Offline Erik_S

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Do rivers have a slope?
« on: 26/10/2009 03:33:55 »
Hello there, long time listener, first time on posting on the forum!

My question is about rivers. I live in New Jersey in the US and there are quite a few rivers around me. I know rivers flow from the lakes and eventually out into the ocean, but my question is: Do rivers have a slope?
I mean to say, in theory, if i were to put a really sensitive carpenter's level on the surface, would it show a slight tilt?

thanks,
love the show!
-Erik


 

Offline Madidus_Scientia

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Do rivers have a slope?
« Reply #1 on: 26/10/2009 03:59:39 »
It would be possible for some parts of the river to be flat, as long as the source of the water is higher than the output. If you floated a level on the surface of the water (and the water was reasonably still) it will show up as level the same way the surface of water in a glass will remain horizontal when you tilt it. But if you put the level on the riverbed it would probably not be exactly level.
 

Offline graham.d

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Do rivers have a slope?
« Reply #2 on: 26/10/2009 09:53:29 »
Generally there is a current flowing in a river and, near estuaries, it will be tidal. As you go inland, away from the sea, generally the river level will increase. Close to estuaries, on a rising tide, the sea end may be higher and water will flow in.

So the answer is that water levels are not constant, though you would not detect any slope with a spirit level and would require a much more sensitive instrument.
 

Offline Geezer

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Do rivers have a slope?
« Reply #3 on: 27/10/2009 03:48:26 »
As Graham.d points out, the slope may be very hard to measure, but if the river is flowing, there will be a very small slope on the surface of the water. If there is no slope, the river cannot flow.
 

Offline Erik_S

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Do rivers have a slope?
« Reply #4 on: 27/10/2009 07:30:45 »
Thanks for the replies guys!

That's another thing i was wondering too, is what Madidus said. Would the river's surface level itself out over a distance, even though the underlying geography/riverbed from point A to B had a slope?

And Graham, slightly off topic and I can't remember exactly where....but i do remember seeing footage on either BBC or Discovery on a river in South America where the incoming ocean tide actually made the current reverse?!
 

Offline graham.d

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Do rivers have a slope?
« Reply #5 on: 27/10/2009 08:51:24 »
It happens everywhere Erik. Famously, the River Severn in the UK forms a tidal bore and certain times of the year; some people have surfed on it for several miles up river.

If you stopped the flow of a river (with a dam for example) the river flow would obviously stop and the water level would be constant. There would be no dependancy on the shape of the river bed.
 

Offline Erik_S

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Do rivers have a slope?
« Reply #6 on: 27/10/2009 23:31:17 »
Thank you graham, that's the word for it...tidal bore. I searched my house an found the dvd's where i saw it. It was a show called Earth hosted by Dr Ian Stewart. Beautiful hi-def footage!

Thanks DiscoverDave for the info! I recently flew to Las Vegas and got an awesome birds-eye view of meandering rivers when i was flying over the middle of the US. So does the way a river deposits or erodes depend on the pressure and speed of the water?

Its funny you mentioned borax. I recently found about the 20-mule teams in the desert. It came up through a google search for rust removal on an old pedal car I'm trying to restore. Apparently '20-Mule Team Borax' was a famous brand name. Go figure lol.
 

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Do rivers have a slope?
« Reply #6 on: 27/10/2009 23:31:17 »

 

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