I used the same sized MDF sections but made the key feature wider than I did the paths.
Making the rivers took a bit longer - I first coated them with caulking and once that was dry I painted the river sections a two tone colour.
Again waiting for the sections to dry I then applied multiple layers of polyurethane to each section progressively over a few days.
Once the polyurethane was dry I built up the banks of the river sections with putty and, you guessed it, waited for that to dry before also painting over the putty.
With that all done I applied another coat of the polyurethane to the rivers and once that had dried I added the flock to the river banks.
One of the river pieces was made up to represent a ford in the river, as seen in the photo above.
I am fairly happy with the end results and I will have to make a few new sections for the path and the river too allow for different directions and to ensure I can fit them both on the playing area with out falling short or going over the edge.