Erosion caused by Sunderland's river (4)
I believe the answer is:
wear
'erosion' is the definition.
(I've seen this before)
'sunderland's river' is the wordplay.
I cannot quite understand how this works, but
'river' could be 'ea' (I've seen this in other clues) and 'ea' is present in the answer.
This may be the basis of the clue (or it may be nonsense).
'caused by' is the link.
Can you help me to learn more?
(Other definitions for wear that I've seen before include "Have on the body as clothes or ornaments" , "Apparel" , "Durham river" , "Clothes; chafe" , "Become damaged by use" .)