Line thickening

[Bill Brown]

> Thus, I have concluded that I need to create buffer zones
> around the streams to improve 3d visualisation

I guess that would help make them visible, but then your streams would
probably be over their banks, so the value of the visualization may be
questionable, depending on what it is you're looking at.

It might be better to just use a higher viewer position.  If your 3d display
program doesn't provide lighting, you might try using a shaded relief 
raster to make up for the loss of terrain cues that result from a higher
viewer position.

-Bill