[GRASSLIST:7280] Hazard Assessment

I am looking at a project which involves a hazard assessment of several hundred kilometres of pipeline route. I need to find where the pipeline crosses valleys and classify the steepness of the approach slopes to the stream.

I have vector coverage of the stream courses and raster DEM topographic data.

How can I extract the locations where the pipeline intersects the streams?

What options are available to classify the steepness of the slope on the pipeline route and perhaps display with a vector line with a width proportional to slope or colour proportional to the slope.

Thanks in advance for any help.

Dave