I've finished my first attempt at making a set of river pieces for 15mm miniatures, using paper and EVA foam.
I start by cutting a piece of blue cardstock that will serve as the base of the terrain module. I used some sheets of linen paper that I had around. The texture is nice but in the end, it didn't make much of a difference because of the cellophane. I think that 12x12cm gives very flexible modules, and 5 of them are enough to cross a standard 15mm battlefield for Song of Blades and Heroes or Hordes of the Things.