# Thread: Is there something like an "average frequency of rivers reaching the sea"?

1. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Originally Posted by Mastikator
And sometimes they actually DO have single point source I used google maps to follow the river nile up as far as a I could (wow that thing goes on forever)
same deal with the daugava river
Thunder River in the Grand Canyon is also a single source river. It emerges from a spring in the side of a cliff face. Yes the volume of water classifies it as a river. It is also one of the few rivers that feeds a creek. And it's only 1/2 mile long.
https://en.wikipedia.org/wiki/Thunde...eek_tributary)

2. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Originally Posted by JCarter426
That's an easy one. Coastlines have a fractal dimension, so their length diverges towards infinity as the precision of your measurement increases. Therefore, the most precise answer is that all coastlines have the same length, and that length is infinite.
It's true enough that Spain/Portugal border (measured on a map of Spain) was significantly shorter than the Portuguese/Spanish one (measured on a map of Portugal).

I'm pretty sure there is often a limit, Egypt's (beachy) coast looks to be pretty smooth quickly from the 20km mark. If so the approx will converge to something not far off say 25km.

In Wales however things are pretty much fractal from 2m (and beneath that point you need to chase rivers anyway) to 20km. https://www.google.com/maps/@51.8870.../data=!3m1!1e3
During this range accounting for each level of bay exponentially increases the length of the coast (although the perimeter has only risen by a factor of less than a million by the time you are using sub-atomic steps.

Functionally I guess you actually want the length of the sailing line (which being at least 100m from any point of the coast will get rid of any of the smaller noise) (and is going to be consistent to about an order of magnitude or two over reasonable scales)

3. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Originally Posted by factotum
Um, isn't the Nile famously formed of the White Nile and the Blue Nile--e.g. two separate major sources?
Yes, and that's pretty common. Going back to strahler order from earlier, the Nile is order 11. That means it has, at minimum 1024 little tiny streams feeding into it once you dig back far enough. In practice that number is way higher (it's fed by a rainforest after all).

4. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Originally Posted by jayem
I'm pretty sure there is often a limit
If nothing else, there is a limit in the real world once you get down to the atomic level, so you could never actually have an infinite coastline.

5. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Originally Posted by factotum
If nothing else, there is a limit in the real world once you get down to the atomic level, so you could never actually have an infinite coastline.
Yeah, and the tide goes in and out twice daily. Mandelbrot was overselling it.

6. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Actually, a lot of places only have diurnal (once a day) tides. And the Mediterranean really doesn't have tides at all.

7. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Originally Posted by Rogar Demonblud
Actually, a lot of places only have diurnal (once a day) tides.
Don't be daft. Tides take 12.x hours on average, so some days there won't be two high tides in a day, or not two low tides, but there will always be at least three of low tides and high tides, the tides moving in and out will always happen. The tides happen when the Earth and the Sun are aligned, that happens once at noon, and once at midnight, but the Moon though much less massive than the Sun is much closer, so the tides of the Sun and the Moon combine, and the tides we get are due to the combination, and take a variable bit over 12 hours to occur.

And the Mediterranean really doesn't have tides at all.
It has to have tides, the Sun and the Moon still exist, they may be very little different from the tidal movement of the land.

8. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Incorrect. The three tide types are semi-diurnal, diurnal, and mixed. See the chart in the link.

9. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Originally Posted by halfeye
It has to have tides, the Sun and the Moon still exist, they may be very little different from the tidal movement of the land.
Yes, it does have tides, but the tidal range across almost the entire sea is a few centimetres and is thus barely noticeable. If the Earth were perfectly spherical, had no continents and the ocean was the same depth throughout, then yes, everywhere would have the same tide depth, but it isn't like that, and so tidal ranges vary massively from one place to another. (I think the reason the Med has such a tiny tidal range is because there's a fixed volume of water in the basin--the only place it could get extra water from for a proper tide would be from the Atlantic, and the Strait of Gibraltar is too narrow to allow those volumes of water to pass through it on the tidal 12-hour cycle).

10. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Originally Posted by halfeye
Don't be daft. Tides take 12.x hours on average, so some days there won't be two high tides in a day, or not two low tides, but there will always be at least three of low tides and high tides, the tides moving in and out will always happen. The tides happen when the Earth and the Sun are aligned, that happens once at noon, and once at midnight, but the Moon though much less massive than the Sun is much closer, so the tides of the Sun and the Moon combine, and the tides we get are due to the combination, and take a variable bit over 12 hours to occur.
Uhm... No. I mean, a bit yes. But mostly no.
As you say, the tides come mostly from the moon, not the sun. So time of day and tide schedule are only remotely connected which is why tides shift forward each day by about 45 minutes (very roughly). The sun also influences water levels but it's usually negligible compared to the moon, so it's mostly noted if the three bodies align and the effect is emphasized or weakened. Of course in theory you have two overlapping wave functions which are not correlated.
(note: can two bodies align? I mean, I think I know what is meant but an alignment of two just sounds wrong to me)

11. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Yes, two bodies can align. Also, in addition to lunar tides and solar tides, there are also sidereal tides. I don't understand those.

12. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Originally Posted by Rogar Demonblud
Yes, two bodies can align.
How? Surely they need a third body to be aligning *with*? (e.g. in the case of the Sun and Moon aligning to create bigger tides, it's the Earth that they're aligning with).

13. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Originally Posted by jayem
I'm pretty sure there is often a limit
Originally Posted by factotum
If nothing else, there is a limit in the real world once you get down to the atomic level, so you could never actually have an infinite coastline.
Originally Posted by halfeye
Yeah, and the tide goes in and out twice daily. Mandelbrot was overselling it.
Typical physics and its "observations" in the "real world" that don't match up to the one, true theoretical reality. I suppose next they'll be claiming that even space isn't continuous and can be quantized.

14. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Originally Posted by factotum
How? Surely they need a third body to be aligning *with*? (e.g. in the case of the Sun and Moon aligning to create bigger tides, it's the Earth that they're aligning with).
Don't ask me, since I'm not an astrophysicist. But they say it, and I presume they understand their field.

15. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

I'm pretty sure whatever you've heard along those lines means there's an implied third body that everyone is assumed to know about--e.g. the Earth in the Sun/Moon tide example.

16. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Two bodies are always aligned. It's one of the base principles of mathematics: the shortest route between two points is a straight line. So yes, they do mean those two are aligning with the Earth, for a total of three bodies.

As for the primary question of the topic: I have a feeling the answer has pi in it somewhere. I have this feeling because I know the length of a naturally formed river is often about pi times the distance between its origin and its end. (Particularly in places like tge Amazon, with few natural obstacles like mountains.) This happens because a river erodes the ground on its outside bends while leaving material on its inside bends, so any individual bend will over the course of its lifetime erode into pretty much a full circle before the river breaks through the little barrier that's left and the entire circle is left dry. So on average a bend at a random point in its life is half a circle, and a river comprised fully of half circles is pi times the length of a straight line between origin and end.

This same process of forming circles probably helps define the width of a river bassin, and any other river that runs into the bassin stops being a seperate river, so the amount of space between two rivers/streams reaching the coast should be something something pi something radius of a bend something. Or something...

17. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Originally Posted by Lvl 2 Expert
Two bodies are always aligned. It's one of the base principles of mathematics: the shortest route between two points is a straight line. So yes, they do mean those two are aligning with the Earth, for a total of three bodies.
When I was talking about the Earth and the Sun being aligned, I certaily wasn't implying any third objects. Sure, two spheres are techically always aligned, but points on the surface of one sphere (in particular the Earth) are not necesarily aligned with the sun, the poles never are, and nor are any points outside a certain number of degrees (22 degrees?) from the equator.

As for the primary question of the topic: I have a feeling the answer has pi in it somewhere. I have this feeling because I know the length of a naturally formed river is often about pi times the distance between its origin and its end. (Particularly in places like tge Amazon, with few natural obstacles like mountains.) This happens because a river erodes the ground on its outside bends while leaving material on its inside bends, so any individual bend will over the course of its lifetime erode into pretty much a full circle before the river breaks through the little barrier that's left and the entire circle is left dry. So on average a bend at a random point in its life is half a circle, and a river comprised fully of half circles is pi times the length of a straight line between origin and end.

This same process of forming circles probably helps define the width of a river bassin, and any other river that runs into the bassin stops being a seperate river, so the amount of space between two rivers/streams reaching the coast should be something something pi something radius of a bend something. Or something...
The lengths of rivers may tend to pi, I don't know about that, however, oxbow bends/lakes tend to be separated by straight stretches of water before the river breaks through the neck and makes them lakes.

18. ## Re: Is there something like an "average frequency of rivers reaching the sea"?

Originally Posted by halfeye
When I was talking about the Earth and the Sun being aligned, I certaily wasn't implying any third objects. Sure, two spheres are techically always aligned, but points on the surface of one sphere (in particular the Earth) are not necesarily aligned with the sun, the poles never are, and nor are any points outside a certain number of degrees (22 degrees?) from the equator.
My apologies, I see, you were just using a weird term for the sun being straight overhead or below a certain longitude, which could be considered an alignment of the tree objects earth, sun and a specific spot on the Earths surrface.

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