Clay is dumped in hollow by river regardless of the consequences (8)
I believe the answer is:
cavalier
'regardless of the consequences' is the definition.
'clay is dumped in hollow by river' is the wordplay.
'clay' becomes 'ali' (Muhammad Ali was born Cassius Clay).
'is dumped in' indicates putting letters inside.
'hollow' becomes 'cave' (caving is a kind of hollowing**).
'by' says to put letters next to each other.
'river' becomes 'r'.
'ali' inserted inside 'cave' is 'cavalie'.
'cavalie'+'r'='CAVALIER'
(Other definitions for cavalier that I've seen before include "Casual" , "Arbitrary, off-hand" , "Roundhead's foe" , "A vile car is offhand" , "... King Charles, canine breed" .)