in present Austria you find 343 entries for
Riedel in phonebook
www.herold.at > english-version > peoplepages > write in the name > refine at county (=austrian states), taking a state you can again refine at district.
Riedel is a usual name, so you need in any case a place to find out more, because the former austrian-hungarian empire was very big.
specially i also know the Riedel-name for "Sudeten-germans" in Bohemia, today Czech.Rep.
example: the famous Riedel-Glass
http://www.riedel.com/familyhistory on page above at "Riedel-family"