Alas, Fran, I'm knee-deep in animating a particle-driven dynamic fountain of blood in Maya. Collision detection per-particle and everything, I don't think I'll have any time soon to waste attempting animation in Bryce... I don't think I'll ever animate in Bryce again, to be honest. It's just really not a good animation tool, and the render times are ridiculous compared to the other tools at hand. I can't justify spending hours in Bryce to do what takes Maya seconds to set up, alas... If you want though, I can show ya how to animate procedural textures to do the waterfall. It's fairly straightforward. Then you just map them to a terrain object... I'll do something for ya this afternoon after I get home from work...? (this is the mess I'm in as we speak)