Severn estuary

Severn Estuary

Site of Special Scientific Interest
Location within Gloucestershire
Area of Search	Gloucestershire
Grid reference	ST480830
Coordinates	51°27′42″N 2°59′47″W / 51.4617°N 2.9965°W / 51.4617; -2.9965Coordinates: 51°27′42″N 2°59′47″W / 51.4617°N 2.9965°W / 51.4617; -2.9965
Interest	Biological/Geological
Area	15950 hectare
Notification	1976 (Brean Down and Uphill Cliff 1952)
Natural England website

The Severn Estuary (Welsh: Môr Hafren) is the estuary of the River Severn, the longest river in Great Britain. It is at the mouth of four major rivers, being the Severn, Wye, Usk and Avon, and other smaller rivers. Its high tidal range of about 50 feet (15 m) means that it has been at the centre of discussions in the UK regarding renewable energy.

Definitions of the limits of the Severn Estuary vary. A narrower definition adopted by some maps is that the river becomes the Severn Estuary after the Second Severn Crossing near Severn Beach, South Gloucestershire, and stretches to a line from Lavernock Point (south of Cardiff) to Sand Point near Weston-super-Mare. The definition used on Admiralty Chart SC1179 and the Bristol Channel and Severn Cruising Guide is that the estuary extends upstream to Aust, the site of the old Severn Bridge. The estuary is about 2 miles (3.2 km) wide at Aust, and about 9 miles (14 km) wide between Cardiff and Weston-super-Mare.

The Estuary forms the boundary between Wales and England in this stretch. On the northern side of the estuary are the Caldicot and Wentloog Levels which are on either side of the city of Newport; and, to the west, the city of Cardiff together with the resort of Penarth. On the southern, English, side, are Avonmouth, Portishead, Clevedon, and Weston-super-Mare. Denny Island is a small rocky island of 0.24 hectares (0.6 acres), with scrub vegetation, approximately three miles north of Portishead. Its rocky southern foreshore marks the boundary between England and Wales, but the island itself is reckoned administratively to Monmouthshire, Wales.