Some Syrian drowned valley (3)
I believe the answer is:
ria
'drowned valley' is the definition.
(I've seen this before)
'some syrian' is the wordplay.
'some' indicates the answer is hidden within the clue (some of the parts of the word are used).
'RIA' is hidden within 'syrian'.
(Other definitions for ria that I've seen before include "Little girl" , "Long narrow inlet" , "Air (anag.)" , "Drowned river valley now an inlet of the sea" , "inlet between hills" .)