NORTHWEST - North of the Severn drainage, flowing to the Irish Sea

NORTHEAST - North of the Trent drainage, flowing to the North Sea

THE MIDLANDS - From the Warwickshire Avon in the south, to the Trent in the north

SOUTHWEST - The Somerset Frome and Dorset Stour and westwards

SOUTHEAST - Hampshire Avon drainage and eastwards, with the Nene as the northern limit

WALES

NORTH - Severn and Rheidol catchment and northwards

SOUTH - South of the Severn and Rheidol catchment

Also, check the WCA site which has the entire text of The Welsh Rivers - fantastic resource!

SCOTLAND

THE NORTHEAST - Rivers 'near' Aberdeen

THE WEST HIGHLANDS - Rivers 'near' Fort William