So having added some surface texture to the water I decided that I still wasn't happy with the stream, specifically the small fall.
The main problem I had with the fall was that the water was following the rock surface, which doesn't happen in real life. In reality water erodes the rock from the top of the fall downwards resulting in the rock having a conave surface, i.e. it drops down before going outwards. Water flowing over the rock though forms a convex shape as the momentum carries it out before gravity pulls it down. With my water following the rock it didn't shoot out enough.
My first thought was to try and build up the water using the Woodland Scenics water effects but I decided I wanted something that naturally had some colour to it and the water effects dries clear. My solution was cotton wool.
So I took a small piece of a cotton wool ball and gently teased it out trying to keep the threads all running in one direction so that they could represent individual falls of water. I then gently tapped this to a bit of folded metal to make it easier to hold before gently wafting on some matt varnish. Once the varnish has dried the teased out cotton wool keeps it's shape remarkably well but still looks nothing like water so the last stage is to paint on a thin layer of the Woodland Scenics realistic water. Once this dries it goes clear leaving a thin film of water with white highlights inside it rather than being painted on the top. A small piece of this is then cut to shape and essentially glued in place using small amounts of water effects which then add more turbulence to blend in the edges.
I think this looks much better than the old falls, although in retrospect I should probably have used a couple of small strips to match the lip of the fall rather than shaping a single piece but I'm not going to try changing it now.