Before you do anything else, carve out your river and place your bark chips where you want your ridges to go. You can terrain around the ridges for now, but the river bed has to go in now. Again you don't need to work on the river yet, just cut it out.
Now...groundwork. Everything else relies on it.
You should try mixing some sand into a couple of dark brown paints, like Chocolate Cherry, Bittersweet Chocolate and so on, using those cheap 2 ounce craft paints like Folkart or CeramCoat. The sand will stick to the panel and break up the surface. It will also harden, protecting your board. Regular sand from the beach or playground is fine. Mix a shot glass full into the 2 ounce craft paint. I use a plastic six ounce drinking cup to mix it in.
Add in a 50 - 50 mix of white glue and hot water and mix it up till it's all one color.
Slop it all over your board with a large brush.
You can mix in a different color browns into the original mixture to vary the colors.
You should end up with a nice sturdy board with a good base to work on.
Let this dry overnight. Two, if your not in a hurry.
After that I drybrush a color called Ochre over the whole surface. This is a yellow with some brownish tint to it. It lightens the chocolate colors nicely.
Next, I do a second drybrush using Folkart Sand color. I run this over the high points and it serves to pick out the "rocks" quite well.
Check out what the bare earth will look like here.
viewtopic.php?f=7&t=31503Let this dry and we can move onto flocking using various turfs, static grasses and clump foliages.
But first, let's see how this works out.
You should check out my terrain pieces here on this board to see examples.