Hi tjj!
That's a really fascinating looking blog you got there! Must have a deeper look when I get a mo... I used to work near Swindon and have the dingiest of memories of it, so it'll do me good to see the brighter side of it! :)
And while we're on the subjects of "hidden" and "rivers", here's a really interesting blog entry I find myself returning to from time to time...
http://lndn.blogspot.com/2005_08_01_lndn_archive.html
G x