Bound over river - it's drained (5)
I believe the answer is:
tired
'drained' is the definition.
(tiring is a kind of draining)
'bound over river' is the wordplay.
'bound' becomes 'tied' ('tie' can be a synonym of 'bind').
'over' indicates putting letters inside.
'river' becomes 'r' (abbreviation).
'tied' going around 'r' is 'TIRED'.
'it's' acts as a link.
(Other definitions for tired that I've seen before include "Beat" , "Worn-out" , "Whacked" , "Played out" , "Physically or mentally weary" .)