Some of my 1/56 Brits posing with a home made river section and a Sarissa bridge...
The bridge was easy to assemble and I painted it with cheap rattle can grey primer and the concrete pylons got a shot of machinery grey. Then I hand painted the walking ramp boards and added a piece of wet and dry sandpaper to road section of the bridge and all sorted! Quick and easy.
For the river I used the gap filler technique I've used with other scales. I used some MDF as a base spread the gap filler then painted it green/blue (a bit too much green in the end buy hey its algea time) with off white highlights. Then I glued some sand to the edges which got a brown wash.
Cheers!