Given relief since being trapped in rising river (5)
I believe the answer is:
eased
'given relief' is the definition.
(I've seen this before)
'since being trapped in rising river' is the wordplay.
'since' becomes 'as' (both can mean 'because').
'being trapped in' is an insertion indicator.
'rising' shows that the letters should be reversed in order (in a down clue, letters go up).
'river' becomes 'dee' (River Dee).
'dee' back-to-front is 'eed'.
'as' put within 'eed' is 'EASED'.
(Other definitions for eased that I've seen before include "Made less difficult, relieved from anxiety" , "Died down" , "Slackened off" , "Lessened, pain or discomfort, say" , "relented" .)