Waterlogged hole covered by turf (6)
I believe the answer is:
sodden
'waterlogged' is the definition.
(thesaurus)
'hole covered by turf' is the wordplay.
'hole' becomes 'den' (I've seen this in other clues).
'covered by' means one lot of letters go next to another (on top of in a down clue).
'turf' becomes 'sod' ('sod' can be a synonym of 'turf').
'den' put after 'sod' is 'SODDEN'.
(Other definitions for sodden that I've seen before include "Muddy" , "'Soaked, sopping (6)'" , "heavy with moisture" , "Waterlogged" , "Drenched, really soaked" .)