I've been monkeying around with a parametric 3D model to make river sections on a 3Dprinter. I'm not done with the model, but I have put together a prototype.
The model produces results for rivers and banks as separate pieces, so a complete river is three pieces: left bank, river, right bank. This allows the parts to be printed in different materials, and allows you to have a wider river than if it was a one-piece model.
The major limitation is that the pieces cannot be longer than your 3Dprinter's print area (which, for me, is about 6 inches in length).
Here's the river model output – it's just a box, two inches by five inches, .125" thick:
And here's a bank piece, which is designed to fit over the river piece:
I chose to orient the models so that they were standing vertically in the printer. I printed the river banks in green plastic, and the river itself in transparent blue:
I suppose you could use the pieces straight from the printer, but I decided to paint and flock the bank pieces, and to apply some gloss coats to the river. I painted the banks a dirt brown color, and the bottoms black. No primer needed, but it takes two to three coats – I paint with the striations first to make sure the paint gets into those crevices, then across the striations while the paint is still wet. Then I sealed with flat spray. For the river, I used about ten fast-drying coats of gloss Mod Podge.
I then applied glue to the banks and flocked them, afterward sealing them again. Then I superglued everything together:
And here it is with a familiar figure to give you a sense of size:
Based on the prototype, I've decided to revise the bank pieces when I work on the model next – figures get 'too tippy' on round banks, and making a curved bank piece uses too many triangles when it's round in two dimensions…