Rhine tributary rougher here and there (4)
I believe the answer is:
ruhr
'rhine tributary' is the definition.
(I've seen this in another clue)
'rougher here and there' is the wordplay.
'here and there' indicates alternate letters (here and then can mean regularly).
The alternating letters of 'rougher' are 'RUHR'.
(Other definitions for ruhr that I've seen before include "German river flowing into the Rhine" , "Herman industrial area" , "Dortmund area?" , "Traditional region of German heavy industry" , "German industrial area" .)