The Bristol Channel (, literal translation: "Severn Sea") is a major inlet in the island of Great Britain, separating South Wales from Devon and Somerset in South West England. It extends from the lower estuary of the River Severn () to the North Atlantic Ocean. It takes its name from the English city of Bristol, and is over 30 miles (50 km) wide at its western limit. Long stretches of both sides of the coastline are designated as Heritage Coast. These include Exmoor, Bideford Bay, the Hartland Point peninsula, Lundy Island, Glamorgan, Gower Peninsula, Carmarthenshire, South Pembrokeshire and Caldey Island. Until Tudor times the Bristol Channel was known as the Severn Sea, and it is still known as this in both and . Geography The International Hydrographic Organization now defines the western limit of the Bristol Channel as "a line joining Hartland Point in Devon () to St. Govan's Head in Pembrokeshire ()". The IHO previously put the western limit at a line from Trevose Head in Cornwall to Skomer Island in Pembrokeshire, in an area now considered part of the Celtic Sea. The upper limit of the Channel is between Sand Point, Somerset (immediately north of Weston-super-Mare) and Lavernock Point (immediately south of Penarth in South Wales). East of this line is the Severn Estuary. Western and northern Pembrokeshire and north Cornwall are outside the defined limits of the Bristol Channel, and are considered part of the seaboard of the Atlantic Ocean or more specifically, the Celtic Sea. According to the officially defined limits, the Bristol Channel is approximately from west to east. Taken as a single entity, the Bristol Channel/Severn Estuary system extends eastward to the limit of tidal influence near Gloucester. The channel shoreline alternates between resistant and erosional cliff features, interspersed with depositional beaches backed by coastal sand dunes; in the Severn Estuary, a low-lying shoreline is fronted by extensive intertidal mudflats. The Severn Estuary and most of the embayments around the channel are less than 30' (10 metres) in depth. Within the channel, however, there is an E-W trending valley 65' to 100' (20 to 30 metres) in depth that is considered to have been formed by fluvial run-off during Pleistocene phases of lower sea level. Along the margins of the Bristol Channel are extensive linear tidal sandbanks that are actively dredged as a source of aggregates and in the Outer Bristol Channel off the