Mercian, thanks for the very interesting link to the web-site about Ted Wright - quite a hero, I will go back to it and read again.

Fascinating subject, water-sheds and which little streams feed into larger rivers. When you start looking into it, it gives a wonderful sense of connectiveness. In the ever expanding town where I live (Swindon) there are some ancient willows growing on a section of the central reservation of the main duel carriageway out to Junction 15 of the M4. When I asked around a bit, it turned out that these trees grew alongside a small river (probably the river Cole) which in turn formed a natural boundary to some farm-land (needless to say no longer there). When the road was widened into a duel carriageway the river was culverted underground and diverted - but the willows still remain as a clue to its presence.

tjj