Flood-control barrier (5)
I believe the answer is:
levee
'flood-control barrier' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for levee that I've seen before include "Artificial embankment" , "Quay" , "River bank reinforcement, particularly in the US" , "Flood embankment" , "Retaining embankment" .)