Flood ruins rebuilt hotel (6)
I believe the answer is:
inrush
'flood' is the definition.
(I've seen this in another clue)
'ruins rebuilt hotel' is the wordplay.
'rebuilt' indicates an anagram.
'hotel' becomes 'h' (phonetic alphabet: alpha, bravo, charlie etc.).
'ruins' with letters rearranged gives 'inrus'.
'inrus'+'h'='INRUSH'
(Other definitions for inrush that I've seen before include "Sudden arrival or entry" , "Sudden entering flow" , "Sudden inward flow" , "hasty entrance" , "gaining sudden entry" .)