Thanks for all your comments!
Yossam - agree with you about the spec on the rocks - think it needs to be broken up a little bit - the texture gets lost there.
Ryan - yes, used the Ivy generator, really impressed with how much geometry you can bring into Terragen and it doesn't complain at all, The rocks were three sizes of fake stones merged with Choose by Altitude to get them to stack up properly. There are a few "pancake" rocks in there annoyingly, but after going through quite a few seeds to find a good variation, it was a case of finding the least offensive one :-)
Lighting in Terragen was mainly a sunlight, but also used an HDR of a similar scene brought into a Background node. Rendered out to Render Elements and comped it in Nuke. As well as the main color passes, I rendered ID passes to tag major elements like the foreground rocks, ivy, shrubs, etc. Then I could boost the global illumination of the back rock walls of the terrain for example - which I might have slightly overdone, hence the background shadow areas Ryan mentioned. But that's easily tweaked in comp now - it was nearly a 5 hour render!
I also used the relighting trick in Nuke to get a kind bloom of light around the waterfall, where the foamy water is almost casting a kind of ambient light. Doing it in the comp meant I could very quickly experiment with the placement of the lights. It does however have to be fairly subtle and the extra lights don't shadow the area they are illuminating, so a bit of contrast is lost in those areas.
The main part of the exercise was getting Terragen and Realflow to work together. It mainly involved exporting the final terrain via the Micro exporter, importing it into Maya, to setup a scene and then exporting that out into Realflow. I only needed the immediate area around the waterfall, so the geometry wasn't that huge, but it did need a lot of cleaning up.
It took a few tries to get a good waterfall simulation, as what seemed like a nice terrain, but didn't affect the Realflow sim in a very "waterfally" way at all. First sim looked like a curtain of water. So it was a bit of a mission going backwards and forwards to find a terrain that look right and perturbed the fluid particles in the right way.
Just to note, the obj mesh that gets exported via the micro exporter contained a lot of duplicate vertices - which makes it impossible to edit in programs like Maya, not to mention huge in file size, found a free prog called Meshlab which does a great job of removing the duplicates and optimizing the mesh too.
The waterfall was rendered out as particles in Maya, and added to the main comp in Nuke. To get the reflection of the waterfall in Terragen, I made a simple bit of geometry and placed in the position of the waterfall, projected the render of the waterfall onto it and set it to be invisible to camera in the final render.
