Eric wrote:
Here's something to think about - and I hope someone has some good
answers or can point me to a good source of info...

I think that local and overall gradient and the kind of soil or rock
through which the river cuts its way also plays a major role in
determining the difficulty level of the river/rapids.

--
Wilko van den Bergh
Eindhoven The Netherlands Europe
Look at the possibilities, don't worry about the limitations.
http://wilko.webzone.ru/