Relieved when sunk in rising river (5)
I believe the answer is:
eased
'relieved' is the definition.
(easing is a kind of relieving)
'when sunk in rising river' is the wordplay.
'when' becomes 'as'.
'sunk in' indicates putting letters inside.
'rising' is a reversal indicator (going up in a down clue).
'river' becomes 'dee' (River Dee**).
'dee' in reverse letter order is 'eed'.
'as' inserted inside 'eed' is 'EASED'.
(Other definitions for eased that I've seen before include "Facilitated" , "Abated" , "Relieved, mitigated" , "Helped" , "became less tight" .)