Thanks all for nice comments!
@Killa Any more info/ pics, mate. Sounds very interesting!
@pastybarm Yeah bristols pretty unique in that it has two huge storms drains that run for miles to the very tidal avon - Motherload and Dreadnaught. These were built in the early 60's because the tidal range is so big and if the tide's high and the frome or malago was in spate the water had nowhere to go. This used to happen often and now doesn't. All of the frome could be diverted down motherload permanently if they wanted to. I'm not sure why it hasn't been - though i'm glad it hasn't!