Susan,

Yes, "en amont / en aval" is absolutely common in French works, for example in books dealing with fortress war (especially on fortresses which are located at an river or "à cheval" of an river). I believe it is in use still today, see for example Robert Ouvrard's book on Iena [Jena] https://books.google.de/books?hl=de&id=UAwiAQAAIAAJ - search for "en amont" resp. "en aval"...

Regards, Thomas