For consideration...
I like river too. Can put a river anywhere really, so plenty of freedom for creativity and personal choice.
However, if you go back and read all of the threads on rivers (more resent ones) you'll see that making rivers in TG requires a lot of irritating hacks. If you read Ulco's threads he had to figure out a lot just to get the water to follow the ground, then there is the unfixable problem of the fact that the water does not flow around curves (not really, though Ulco kinda made it look like it did, some times).
Of course people will think of water falls when they are generating ideas for them selves... look at the water fall threads. Water is simply not a strong point of TG, with all respect to the people who do pretty amazing things with it. But in my very humble opinion, for most people, a contest on making rivers in TG will be a frustration where results are concerned, compared to normal terrains.
How will you do rapids and bubbles and sediments and so on and so on. Yes, it can be done. But not by everyone, and never as well as in other 3D apps that do water well. caustics? Anyone? Nope.
Of course my criticism dose not include lakes and ponds and such, which TG can do really well for the most part, and which everyone who has TG can figure out pretty easily. But a river is arguably a more (potentially) complex ecosystem even just at the mechanical level.
The thing about the Iceland contest that was so great is that is focused effort, provided inspiration at a huge level, and remained open enough that you could do pretty much anything with it, minus a palm tree.
I understand wanting to do something completely different this time. But I would just say that the really good parts of the Iceland contest should also be put into to this contest. So something that helps focus direction such as (but not necessarily) a specific place. And which allows for a lot of freedom of choice.
Of course all I wrote may be moot if there will be a update soon, that makes rivers more practical and realistic in TG, and slightly less difficult if Ulco releases his river nodes for all
Anyway, I don't know. But I just think we will end up with a lot of good TG terrains and a "U" shaped negative displacement with a lake node dropped in in a valley.
As for me, I was already thinking about how I could use other apps to make both the river bed and the water to use in TG.
Or I guess you could just use clouds
