Rivers are a pretty big deal in terms of what they can do for transports, as well as placing a capital.
Your images turned out really good. If I get a good unified terrain style going, I will take a stab at rivers at the same time I get the shoreline tiles worked out.
Edit: I'm looking at it, and those might be quite a bit of work in terms of making them continuous with each other. I'm thinking I might blow your first picture demonstrating the continuities up so that each square is 512x512, and using it as a template to pound them all out in a giant tilesheet. It will take some tweaking to get right I'm sure, but I think it will still be faster than doing each one individually.
Also, I can quarter the work involved by rotating these tiles. I could even cut that in half again by mirroring and rotating the first tile. It wouldn't be as pretty as it could be, but it would get us the 20 river tiles with four original tiles. I could do the same with one mouth and one head tile each.
As in the original rivers cannot fork or join. However this is not an essential limitation. If we want that and give it enough priority we will have that.
In my opinion that would be a lot of work, because splitting rivers will no look reasonable unless we have different widths on them.
River deltas would be nice too.
This would be easy to implement. I draw the 8 river mouths, and 8 deltas that take up a single tile. If the river meets the ocean on a green plains tile, we can lay the delta; otherwise, we just lay river mouth so we don't have a giant delta eating up an apple orchard or something.
Any improvement is welcome but has low priority. So it's more for times when you haven't anything else to do.
