These cost a little bit of money, but check out the "Poseable Moderate Flow Stream" or the "Poseable Swift Flowing Stream" at C3D. These are infinitely malleable and can be used thousands of times, each in a different way. Shape them to fit any terrain, or easier yet, build a terrain or scenes around them. Lay out duplicates end to end to make long streams. Zoom in for close-ups.  Not trying to sell you anything really, but these were built just to make your kind of task much easier.  

If there is enough interest, I'll put them into the market here.

I'm working on a wider poseaable stream now, and another with stepped pools. But they take time and effort to develop. Lots of unsatisfactory results for everyone that turns out well enough to put into the marketplace.