Stick stuck in rising river wore away (6)
I believe the answer is:
eroded
'wore away' is the definition.
('erode' can be a synonym of 'wear away')
'stick stuck in rising river' is the wordplay.
'stick' becomes 'rod' (I've seen this before).
'stuck in' is an insertion indicator.
'rising' is a reversal indicator (going up in a down clue).
'river' becomes 'dee' (River Dee).
'dee' written backwards gives 'eed'.
'rod' placed into 'eed' is 'ERODED'.
(Other definitions for eroded that I've seen before include "Worn away, ground down" , "Wore away" , "Worn away by time, wind or water" , "Eaten away" , "Worn away by weather or water" .)