Hello,
Actually, the "waterway=derelict_canal" would be on the "formerly wet bit" and the "bridge=aqueduct" would be on the whole area.
There is already a linear waterway=canal through here which you can see at https://map.atownsend.org.uk/maps/map/map.html#19/52.73701/-2.56783 .
Best Regards,
Andy