Search for the following lines in the beginning of terrain.cfg file:
//Stream Lines
[Texture.1024] // stream lines / unknown / perennial
Type=1
Size=4
ExcludeAutogen=1
MaskClassMap=3
Textures=RiverSU.bmp
offset=-10
[Texture.1025] // stream lines / unknown / non-perennial
Type=1
Size=4
ExcludeAutogen=1
MaskClassMap=3
Textures=RiverSU.bmp
offset=-10
To prevent this problem, change the offset value to offset=0 . This is a global setting for Flight Simulator. For the roads, the default value is offset=flat. You can also change this value to offset=0 in order to avoid conflicts between the roads and the mesh.
This problem will not occur if you are using standard Flight Simulator roads and rivers.