There’s flooding with river unwanted in Cambridge college (7)
I believe the answer is:
downing
'cambridge college' is the definition.
'there's flooding with river unwanted' is the wordplay.
'there's' is a charade indicator (letters next to each other).
'flooding' means one lot of letters goes inside another (some letters flood or submerge others).
'with' becomes 'w' (abbreviation).
'river' becomes 'Don' (Yorkshire river).
'unwanted' becomes 'ing' (I can't justify this - if you can you should believe this answer much more).
'w' put within 'don' is 'down'.
'down' put next to 'ing' is 'DOWNING'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for downing that I've seen before include "and 17: Thoroughfare of government" , "College of Cambridge" , "Drinking" , "Street that houses British P.M." .)