On the list of terrain I still have to prepare for playing SSOM is a good set of river tiles, including corners and so on. I cut up a few 100 x 250 mm sheets of pp, 2 mm thick, and started cutting 50 mm wide masking tape.
I cut it in a wavey line, then glued the straight edges in the middle to get a natural flow while still keeping a 50 mm width. On both edges I indicated a 25 mm bank, in order to make sure the rivers fit together well.
I made a total of 8 straight pieces, that's 2 meters of river, and some corners, 4 straight corners, and a ford.
Using leftover strips of foam I made the rought bank shapes. After doing all the pieces I cleaned up the edges and made sure the banks more or less aligned. Not perfectly, but I managed to get rid of the biggest misses using an exacto and a big dollop of patience.
I cut roughly and let the glue dry overnight before starting to refine the shapes: that way I avoided tearing off pieces of foam.
I made up a bowl of home improvement plaster, and started smearing and sculpting. Quite a lot of plaster went into it, but I did manage to get all corner parts done, and partly finished the ford. With the plaster not yet completely dry, I start tearing off the masking tape.
Apart from a few smudges, this makes for very nice edges. The smudges will probably remain, I might try to clean them up later, but it just adds a bit of irregularity.