Below are the rest of the ditch steps.
Couple more notes:
In the last screenshot above, I ended up making the surface 1-sided and flipped the normals.
Also, this makes a rather high-polygon ditch. If you need lower resolution, the Object -> Reduce command works very well. (You may want to commit subdivisions before performing a Reduce.)
Finally, you can find the Noise plugin at
http://supercoldmilk.com/ac3dplug/noise.html
HTH