I remember reading something once about removing river trenches from the sim via editing the fs9.cg and changing one of the TERRAIN lines.
I have forgotten what to do though- could anyone remind me please?
Ahh, found the fix mysef:
Remove ”canyons” and other Mesh weirdness in photographic sceneries
This is caused by the ”valleys” FS9 creates for rivers/streams. When you're using a photographic scenery, the actual stream lines are not drawn. The stream lines you see are actually part of the photo texture. The Microsoft stream lines and the actual photographic stream lines are rarely aligned because Microsoft uses very innacurate stream line data. This causes ”valleys” or canyons to appear in the scenery near rivers or streams.
In your FS9 folder, find and open terrain.cfg. Near the top, you should see:
Under this are textures 1024 and 1025. At the bottom of each offset=-10
For textures 1024 and 1025 (stream lines), change it to read:
You may want to set it back to -10 when you're not flying over photographic scenery.