Good grief Ian, are you mind reading me over there in chilly Canada or what?
Take a lookee at this web site I have under development this week.
Only a few pages are up there yet and available to read but you can see the one on viaducts too ...
Thomas Bouch had actually started building his own Forth Bridge design for the North British Railway when his Tay Bridge just to the north took its famous nosedive in December 1879. Otherwise you would have been looking at quite a different bridge over the Forth at the moment. You can still see bits of his foundations out there in the estuary.
Another fine mess he nearly got everyone into eh?
I hope I see that big iron bridge you have in Edmonton someday.