I'm looking for a set of outlines of the river basins in the UK - I don't need a particularly detailed or highly accurate map - just a map saying point X will drain into the Thames or point Y will just go into the sea! Just the main river names would be fine. I have the full Environment Agency rivers set and the OS DTMs if I want... but how do I convert this into a catchment boundary?
ps. Sorry about the poor tagging I can't find suitable existing and I don't have the rep to create new ones.