Managed to contain some inundation in downpour (4)
I believe the answer is:
rain
'downpour' is the definition.
(I've seen this in another clue)
'managed to contain some inundation' is the wordplay.
'managed' becomes 'ran' (I've seen this in another clue).
'to contain' is an insertion indicator.
'some' suggests taking the first letters.
The first letter of 'inundation' is 'i'.
'ran' going around 'i' is 'RAIN'.
'in' is the link.
(Other definitions for rain that I've seen before include "Falling moisture" , "Precipitation" , "Wet weather" , "Fall wetly" , "Weather - shower" .)