The Severn Estuary (Welsh: Aber Hafren) is the estuary of the River Severn, flowing into the Bristol Channel between South West England (from North Somerset, Bristol and South Gloucestershire) and South Wales (from Cardiff, Newport to Monmouthshire). Its very high tidal range, approximately 50 feet (15 m), creates valuable intertidal habitats and has led to the area being at the centre of discussions in the UK regarding renewable tidal energy.
The England–Wales border, sometimes referred to as the Wales–England border or the Anglo-Welsh border, runs for 160 miles (260 km) from the Dee estuary, in the north, to the Severn estuary in the south, separating England and Wales.
It has followed broadly the same line since the 8th century, and in part that of Offa's Dyke; the modern boundary was fixed in 1536, when the former marcher lordships which occupied the border area were abolished and new county boundaries were created. The administrative boundary of Wales was confirmed in the Local Government Act 1972. Whether Monmouthshire was part of Wales, or an English county treated for most purposes as though it were Welsh, was also settled by the 1972 Act, which included it in Wales.
The Severn-Trent flyway is a migratory route, or flyway, used by birds crossing Great Britain from the Humber estuary to the Severn estuary or vice versa. It follows the Humber and its tributaries the rivers Trent and Tame, then the River Severn. The last of these is not connected to the other three, and so birds must cross the gap over the West Midlands conurbation, around Birmingham.
It is used by birds migrating locally, within Britain, and by those migrating to or from Northern and Southern Europe.