A little bit of feathering along the edges of the contours would make them blend together nicely, I think. Did you texture the center part of the river channel, too? Reducing the opacity of the water a touch more might let it show through better if you did. If not, then I'd say the water's opacity is about perfect.
It's got a nice illustrative look to it. Maybe a little bit cartoony, but that's not a bad thing if it suits the mood you're after.