Nearly ripped, riven by deluge (7)
I believe the answer is:
torrent
'deluge' is the definition.
('torrent' can be a synonym of 'deluge')
'nearly ripped riven by' is the wordplay.
'nearly' means to remove the last letter.
'ripped' becomes 'torn' ('torn' can be a synonym of 'ripped').
'riven' becomes 'rent' ('rend' can be a synonym of 'rive').
'by' is a charade indicator (letters next to each other).
'torn' with its last letter taken off is 'tor'.
'tor'+'rent'='TORRENT'
(Other definitions for torrent that I've seen before include "Turbulent, swift-flowing stream" , "Rush of water" , "Overwhelming outpouring" , "Violently fast stream of water" , "Rapid stream" .)