The flickering lines at a distance suggests to me one of two things:
- A too-high resolution .tga for the LOD, or
- The need to raise the texture some distance above ground level.
The second cause is not likely to be in effect if only a *part* of a texture flickers. But if the whole texture flickers, this height issue could be worth looking into.
As a check on things, try this. When the flicker is observed to be occurring, change the FOV to a notably more zoomed-in level, which will expand the image scale and thereby reduce any undrsampling. If this stops flicker, the .tga should be made to lower resolution or the LOD distance decreased.