There is not much you can do right now, it is a weak point in the Trainz series. Hopefully it will get fixed sometime in the next version where we can have flowing water, especially going down hill.
If you can tell us what it is that you can't quite get right with your river we might be able to give you a hand. There are some reasonable river splines on the DLS but actual water looks better. If you are having difficulty with slope and creating the correct water level there are a couple of things you can do. First, you can use the water features close (within immediate visual distance of your track) and then create the remainder with water splines. Similarly, you can use short stretches of water spline to separate changing water levels. As long as each stretch of water (using the water tool in surveyor) does not touch each other you can alter the water height at each level.
Regards
Bob
Because at the core it's a 13 year old piece of software. T:ANE is addressing that. Incidentally, the other much more recent main competitor to Trainz doesn't do flowing water either, though generally the water decals look more realistic.
For the OP, try checking out the river splines created by clam1952, on the DLS, these are more realistic than some of the earlier or built in stuff.
