Rainwater channel (5)
I believe the answer is:
gully
'rainwater channel' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for gully that I've seen before include "Water-course" , "Narrow channel - fieldsman" , "Water-worn ravine - fielding position" , "one in the field" , "Cricket position; ravine" .)