Sweeping, managing to cover stretch of river (3-8)
I believe the answer is:
far-reaching
'sweeping' is the definition.
(thesaurus)
'managing to cover stretch of river' is the wordplay.
'managing' becomes 'faring' (as in 'how are you faring?').
'to cover' is an insertion indicator.
'stretch of river' becomes 'reach' (reach can mean a stretch of a river).
'faring' placed around 'reach' is 'FAR-REACHING'.
(Other definitions for far-reaching that I've seen before include "Wiith extensive effect" , "Widely-applicable" , "Widespread" , "Wide-ranging" .)