See also notes in the rapid_poly layer. The tagging is basically the same.
RP: mainly fine. the only problem is what to do with the name. the piece of river it replaces will have a name which needs to be included, as will the rapids. how do we name both on one segment? a relation for the whole river may be the only way
HB Aug 2012: osm Whitewater_sports wiki suggests "whitewater:section_name". We don't know the grade so I've just called it whitewater=rapids. With that, looks ok to me.
See ML discussion here: