river help needed

[LynnB]

I guess this could have gone into scenery.
I've been thinking about putting in a 3" x 3foot river but I'm a bit leary about going at it and possibly just need some suggestions and maybe ...
So here's the issue , I have plywood top with seveal support beams underneath( not an issue to cut through) , I want a stone/ gravel river bottom rocks protruding, I want the river to have some depth , I need the banks to allow the fsm super saw mill to not be too high about banks as rail has to be able to be used. I know its not a real big deal to make a river bottom.I got the Frarey modeling water dvd for xmas and he shows how to do an awsome river but the river is a stand alone for scenery only and interferes with no rails or structures. What I'm thinking is either cut a long strip\hole into the plywood top and building up the base\river bottom or using 3/4 white foam board as the river banks and build up.

Here's some pics of the area , you can see the large foot print out of paper and the river will have to come off the two bridges and behind the sawmill will need to be a moving pool then to the river and perhaps finish the river going into the stone culvert into side of hill. I would like to have the river bottom a 1/2" lower than the sawmill pool like a small falls\rapids dropping into the river bottom , this adds to the problems I think . The brown paint is river size. Also you can see the switch which will hold a rail for the sawmill and if need be I can probably raise the rail a bit to fit better for the sawmill.

So any thoughts?