Help to cross river, dried up? (4)
I believe the answer is:
arid
'dried up?' is the definition.
(thesaurus)
'help to cross river' is the wordplay.
'help' becomes 'aid' ('aid' can be a synonym of 'help').
'to cross' indicates putting letters inside.
'river' becomes 'r'.
'aid' going around 'r' is 'ARID'.
(Other definitions for arid that I've seen before include "Dry and sere" , "Parched and barren" , "Without water" , "Drought-hit" , "Sterile" .)