By way of channel bridge (7)
I believe the answer is:
viaduct
'bridge' is the definition.
(viaduct is a kind of bridge)
'by way of channel' is the wordplay.
'by way of' becomes 'via' (I've seen this before).
'channel' becomes 'duct' ('duct' can be a synonym of 'channel').
'via'+'duct'='VIADUCT'
(Other definitions for viaduct that I've seen before include "Long arched structure" , "Bridge across a valley" , "Type of bridge" , "Bridge-like structure" , "Long bridge over land" .)