Astute move to cross river before a flood (8)
I believe the answer is:
saturate
'flood' is the definition.
(I've seen this before)
'astute move to cross river before a' is the wordplay.
'move' indicates anagramming the letters.
'to cross' is an insertion indicator.
'river' becomes 'r' (abbreviation for river).
'before' says to put letters next to each other.
'astute' is an anagram of 'satute'.
'r'+'a'='ra'
'satute' going around 'ra' is 'SATURATE'.
(Other definitions for saturate that I've seen before include "Drench thoroughly, soak" , "Use attar to make thoroughly wet" , "Soak completely" , "flood" , "Make thoroughly wet, soak" .)