Parking by river where tents pitched (4)
I believe the answer is:
camp
'tents pitched' is the definition.
(a camp site)
'parking by river' is the wordplay.
'parking' becomes 'p' (abbreviation on road signs).
'by' means one lot of letters go next to another.
'river' becomes 'cam' (river in Cambridge, England).
'p' after 'cam' is 'CAMP'.
'where' acts as a link.
(Other definitions for camp that I've seen before include "Bivouac, group of tents" , "the military life" , "Extensive outdoor facility" , "holiday venue" , "Temporary military site" .)