[Award Winner] Tutorial on Meandering Rivers in Photoshop

[Zaianya]

There is no Liguify filter in GIMP.
One can use Filters>Distorts>Warp but it doesn't display the circle and (I believe) the circle radius is limited in size so no large loops.

I just found this tutorial today. It's very useful for Photoshop users, thus I repped it--sadly I have GIMP. I played around with the IWarp feature, but it doesn't really produce the same results. However, even if the technique can't be applied, the information certainly can, so thank you for writing this!

EDIT: I forgot to add that perhaps there's a plugin for GIMP somewhere out there that could achieve the same / a more similar effect? If anybody knows and posts a link here, that would be splendid.

[altfritz]

So where a river is narrower it is always deeper? Isn't merely being forced between banks that are too high for it to overflow? I've been trying to re-draw some of the old maps of Tékumel (aka The Empire of the Petal Throne). My favourite version of the maps are those from the Swords & Glory Sourcebook which came out in the early 1980's. The main river in the Tsolyáni Empire is called the "Mssúma" or "Missúma" river. It is stated to be laden with yellow silt. There is meant to be a delta but the map doesn't actually show one - at least no distributary rivers are shown.

So...I went looking for RW examples. I downloaded an entire map set of the Indian Subcontinent from the University of Texas map library. This shows the Brahmaputra, Ganges and Indus rivers, plus many others. All the stuff you mention in your tutorial is visible on these maps. They also include what seems to be an attempt to map what the rivers look like in full flood. Note that they do warn that the path of the rivers are not fixed and will change over time. But there are also regions that may be sand bars.

I know the Mssúma river floods and would really like to figure out how much to allow for this. I have an area that is like the Tonle Sap lake in Cambodia which expands (ten-fold IIRC) in the monsoon season.

http://heroesoftheage.blogspot.ca/se...zing%20Tékumel

http://4.bp.blogspot.com/-ipN8Lrz1IF...o-03122014.jpg

The solid yellow is the river...at the time I was using that colour as the river fill because the water was that colour...

The yellow-tan speckled areas are those areas that may or may not flood depending upon how high the waters get...

Howard

[Chick]

Let's take a fixed point on a river bank. If you consider that a given volume of water has to pass that fixed point in the same amount of time as for any other point, there are two ways that can happen.

1. The flow rate stays the same, and therefore the volume of the river must stay the same. This means if the river is forced narrower, it must also be deeper, to provide the volume (in effect, the cross-section area at that point).

2. The volume (or cross-section area at that point) is smaller because the river is forced narrower but does not (or cannot) get deeper at that fixed point, but then the flow rate must increase, to carry that same volume of water past that fixed point in the same amount of time.

So at a narrows, the river must be either deeper or faster than it is at a wider spot.

As for your maps, I think the way you have depicted the river channel itself, and the floodplain looks quite good.

[altfritz]

Thanks!

I was going to mention the Venturi effect (or rather ask if it didn't apply) causing the water to flow faster... :-)

[Chick]

Yes, what I said is how you explain the Venturi Effect, but for rivers, over long times, that faster flow tends to erode more, and so the river either widens or deepens, depending on surrounding rock, and you get back to the more general "deeper where narrower".

[Corilliant]

I wonder if this works in PS Elements...although knowing how stingy Adobe is getting, it probably doesn't

Congrats on your award!

[Chick]

Thank you, Corilliant!

Please let me know if it doesn't work in newer PS's.

Cheers,
Cornelia

[Naeddyr]

I love these kinds of smaller and specialised tutorials, and this one's yet a further step of progress in river-making techniques.