Journal preserves evidence of pile-ups on the river (7)
I believe the answer is:
logjams
'evidence of pile-ups on the river' is the definition.
I can't tell whether this definition defines the answer.
'journal preserves' is the wordplay.
'journal' becomes 'log' (log can mean a journal or diary).
'preserves' becomes 'jams' (jam is a kind of preserve).
'log'+'jams'='LOGJAMS'
Can you help me to learn more?
(Other definitions for logjams that I've seen before include "Stoppages caused by unusual activity" , "blocks of wood" .)