Number first to forage on river with its banks cleared (4)
I believe the answer is:
five
'number' is the definition.
(five is a number)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for five that I've seen before include "Enid Blyton's famous number?" , "Top-quality hotel has these stars" , "Quintet" , "Cube root of 125" , "V as a numeral" .)