All this considered, we divided the polystyrene board into 2 foot sections. the plain tiles are one inch thick and the river sections are made up of two half inch pieces sandwiched together. In our previous exploit we used 2x4 pieces. The top piece is cut in the river bed and attached to the bottom piece with either hot glue or polystyrene glue. Smooth rocks and some gravel were added to the river bed.
A paint/texture mixture was then applied to all the ground surfaces.
Till then, Have a Great Battle!
The Old Crow