Cheers Bullet, You have filled me with sooo much hope

It is the creating of the environment geometry that I am worried about for the time being, not simulating the river flow. I still have a lot to learn before I dare attempt that. I am also unsure how to determine the overall scale of each section of the terrain (mountains, flat land, lake etc..) and then a consistent depth of the river, for it entire length!

There seems to be very little tutorials on this subject on the net, unless you have access to something like Vue? My only other train of thought is going down the game route and and installing UDK or CryEngine3 SKD on my windows partition (im glad I still have that) as I believe they both have easier ways of creating large landscapes, but I am unsure if you can export the landscape meshes out once created...

Doesn't look like it will be very easy at all.