In reply to Kean:
I think I've seen reference to this in the front of an FRCC guide but didn't spot any usage in the text, and the explanation in the guide wasn't terribly clear.
Personally I wouldn't use the term. It might be nice and quirky, but it's not in common enough usage (in the UK at least) to be widely understood and will lead to confusion. You could well put an explanatory note into the front of the book, but that's eating into page space that you might want to use on something else. Furthermore, it's likely to be overlooked by 90% of your readers who will never look at those introductory pages. And even more furthermore, it might be that the person reading your book is trying to do it while at the same time walking along a rocky footpath and wiping sweat from their brow, so you may not have their full attention.
I'd go with "keep the river on your right" which is immediately understandable. If it's becoming repetetive or clunky then refer to the cardinal points.