River myth?

[Rob_Webb]

I've heard several times that in the N hemisphere river estuaries tend to be deeper on the S side. And that the converse is true in the S hemisphere. To the extent that I've now started to believe it.

Is this for real? And if so what's the explanation?

Cheers

 

[Cornishman]

It would be difficult to believe that of the Tamar which in general runs North - South!

 

[Judders]

[ QUOTE ]
It would be difficult to believe that of the Tamar which in general runs North - South!

[/ QUOTE ]

I was going to say that. The theory does not seem utterly ludicrous though. Funnilly enough I got hold of charts, only yesterday, for a load of rivers in Essex which do run west to east but naturally they're not with me at work.

 

[Sybarite]

Possibly. Water running out of a bath circles one way in the northern hemisphere and the other way in the southern.

I was in Africa on the Equator and this was demonstrated by showing water run out of a basin with a hole in it. By walking a few yards the sense of the rotation changed and directly on the Equator it just ran out without swirling.

John

 

[Lakesailor]

But the scouring effect of bends in a tidal or non-tidal river would surely place the channel on the outside, whether North or South?

There won't be many straight, non-tidal, east-west running rivers to test the theory on, will there?

 

[snowleopard]

The water in the bowl demonstration was exposed as a clever fake on this site just a few weeks ago. It is done by walking with the bowl then turning to face the audience in the appropriate direction. In fact the demonstrators had got the direction wrong in any case!

 

[Rob_Webb]

As often seems to happen when the question is stupid/dull/boring, I seem to answer it myself later:

River estauaries are generally deeper one side than the other.

The exact explanation is a bit complex/dull but basically it's caused by a combination of:

1. The Coriolis effect (which is the by-product of the earth's rotation which cause things to flow non-linearly).

2. Different densities and behaviours of salt water and fresh water.

The end result when you combine these two factors is that in the N hemisphere the fresh water flowing out of a river tends to be deflected to the right (as you look out). And in the S hemisphere it's to the left.

And the (fresh) water flow out to sea is generally faster than the (sea water) flow back into the river. Hence the channel is gouged deeper.

So looking down the Weiti (here in NZ) as you come out, the faster flow (and hence deeper water) will be on the left hand side. If you were coming down the Thames in London the deeper side of the estuary will generally be on the right.

The above explanation is slightly oversimplified but by this stage:

1. You get the point (if you're still reading this far)
2. I'm bored

 

[AliM]

I think the Coriolis effect acts on a N-S river, but shouldn't make any difference to a E-W river. Since no river is straight or exactly E-W (or W-E), I imagine that the local rocks, wrecks, tides and the scouring effect on the outside of bends would be the strongest effect. Therefore, I'd expect it to be a myth, but am willing to be proved wrong by anyone who cares enough to do a bit of research.