IIRC you can add / edit a line in the Fs9 Terrain.cfg file to make them less like canyons....
Found it :
In the Terrain.cfg file ; which resides in your main fs9 folder, the first two sections each contain a line that says
Offset = (and then a number, by default this is set to -10)
Change the Offset = to -3 / -4 or if you have UT try 0 or -1
in both sections, so the line now reads ( for example)
Offset=-3
Use a bit of trial and error, and don't set a positive number or your rivers will end up looking like levees ( or dykes if you're this side of the pond .... as in raised above level of surrounding terrain ... not females with dodgy dress-sense )
Ttfn
Pete