Petite female engulfed by rising river (5)
I believe the answer is:
elfin
'petite' is the definition.
(I've seen this before)
'female engulfed by rising river' is the wordplay.
'female' becomes 'f' (abbreviation).
'engulfed by' indicates putting letters inside.
'rising' is a reversal indicator (going up in a down clue).
'river' becomes 'nile' (Nile is an example**).
'nile' back-to-front is 'elin'.
'f' inserted within 'elin' is 'ELFIN'.
(Other definitions for elfin that I've seen before include "Small, with delicate frame" , "Delicate, slight" , "Small, delicate and charming" , "Little, charming and naughty" , "Sprightly" .)