Obstructs free passage with much timber (5)
I believe the answer is:
clogs
'obstructs' is the definition.
(clogging is a kind of obstructing)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for clogs that I've seen before include "Wooden-soled shoes" , "Wooden shoes" , "11 across shoes" , "Sabots" .)