Flood at lower level on river's banks (5)
I believe the answer is:
drown
'flood' is the definition.
(I've seen this before)
'lower level on river's banks' is the wordplay.
'lower' becomes 'down' (synonyms).
'level on river' becomes 'r' (I can't explain this - if you can you should give a lot more credence to this answer).
'banks' is an insertion indicator.
'down' enclosing 'r' is 'DROWN'.
'at' acts as a link.
Can you help me to learn more?
(Other definitions for drown that I've seen before include "Flood (an area)" , "Submerge, maybe fatally" , "Sink" , "Suffocate in liquid" , "Go under" .)