I stubbled across this website of old disused railways by chance and wish to share it with you.
Although not of Bristol there are some railway relics covered that are quite nearby, ie The Old Severn Railway Bridge.
http://disused-rlys.fotopic.net/
Disused Railways
Disused Railways
A Bristolian living in Swindon
Re: Disused Railways
Interesting site, I will have to find some time to take a more in depth look