The Severn Estuary ( cy, Aber Hafren) is the

estuary An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environment ...

of the

River Severn , name_etymology = , image = SevernFromCastleCB.JPG , image_size = 288 , image_caption = The river seen from Shrewsbury Castle , map = RiverSevernMap.jpg , map_size = 288 , map_c ...

, flowing into the

Bristol Channel The Bristol Channel ( cy, Môr Hafren, 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 Seve ...

between South West England and South Wales.Natural England Severn Estuary SSSI information on the citation, map and unit details
/ref> Its high

tidal range Tidal range is the difference in height between high tide and low tide. Tides are the rise and fall of sea levels caused by gravitational forces exerted by the Moon and Sun and the rotation of Earth. Tidal range depends on time and location. ...

, approximately , means that it has been at the centre of discussions in the UK regarding renewable energy.

Geography

Definitions of the limits of the Severn Estuary vary. At the upstream boundary, the tidal limit of the river is at

Gloucester Gloucester ( ) is a cathedral city and the county town of Gloucestershire in the South West of England. Gloucester lies on the River Severn, between the Cotswolds to the east and the Forest of Dean to the west, east of Monmouth and east ...

. Downstream, the

International Hydrographic Organization The International Hydrographic Organization (IHO) is an intergovernmental organisation representing hydrography. , the IHO comprised 98 Member States. A principal aim of the IHO is to ensure that the world's seas, oceans and navigable waters a ...

places the boundary between the estuary and the open sea of the

at a line between

Sand Point, Somerset Sand Point in Somerset, England, is the peninsula stretching out from Middle Hope, an biological and geological Site of Special Scientific Interest. It lies to the north of the village of Kewstoke, and the stretch of coastline called Sand Bay ...

(immediately north of

Weston-super-Mare Weston-super-Mare, also known simply as Weston, is a seaside town in North Somerset, England. It lies by the Bristol Channel south-west of Bristol between Worlebury Hill and Bleadon Hill. It includes the suburbs of Mead Vale, Milton, Oldmix ...

) and

Lavernock Point Lavernock ( cy, Larnog) is a hamlet in the Vale of Glamorgan in Wales, lying on the coast south of Cardiff between Penarth and Sully, and overlooking the Bristol Channel. Marconi and the first radio messages across open sea Following over ...

(immediately south of Penarth in south Wales). This definition is used by the Severn Estuary Partnership and Visit England. A narrower definition adopted for navigation purposes by some maps includes only the area downstream of the

Second Severn Crossing or cy, Pont Tywysog Cymru, label=none, italic=unset , carries = M4 motorway (6 lanes) , crosses = River Severn , locale = South West England / South East Wales , maint = National Highways , architect ...

near Severn Beach,

South Gloucestershire South Gloucestershire is a unitary authority area in the ceremonial county of Gloucestershire, South West England. Towns in the area include Yate, Chipping Sodbury, Thornbury, Filton, Patchway and Bradley Stoke, the latter three forming part ...

. The definition used on Admiralty Chart SC1179 and the

and Severn Cruising Guide is that the estuary extends upstream to

Aust Aust is a small village in South Gloucestershire, England, about north of Bristol and about south west of Gloucester. It is located on the eastern side of the Severn estuary, close to the eastern end of the Severn Bridge which carries the M ...

, the site of the

Severn Bridge The Severn Bridge ( cy, Pont Hafren) is a motorway suspension bridge that spans the River Severn between South Gloucestershire in England and Monmouthshire in South East Wales. It is the original Severn road crossing between England and Wale ...

. On the north-west (Welsh) side, the rivers Wye and

Usk Usk ( cy, Brynbuga) is a town and community in Monmouthshire, Wales, northeast of Newport. It is located on the River Usk, which is spanned by an arched stone bridge at the western entrance to the town. Usk Castle, above the town, overlooks th ...

flow into the estuary, and on the south-east (English) side, the River Avon joins at

Avonmouth Avonmouth is a port and outer suburb of Bristol, England, facing two rivers: the reinforced north bank of the final stage of the Avon which rises at sources in Wiltshire, Gloucestershire and Somerset; and the eastern shore of the Severn Es ...

. West of the Wye, the estuary forms the boundary between

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

and

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

. On the northern side of the estuary are the

Caldicot and Wentloog Levels The Caldicot and Wentloog Levels are two areas of low-lying estuarine alluvial wetland and intertidal mudflats adjoining the north bank of the Severn Estuary, either side of the River Usk estuary near Newport in south east Wales. They are als ...

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

, Portishead,

Clevedon Clevedon (, ) is an English seaside town and civil parish in the unitary authority of North Somerset, part of the ceremonial county of Somerset. It recorded a parish population of 21,281 in the United Kingdom Census 2011, estimated at 21,442 ...

, and Weston-super-Mare. Denny Island is a small rocky island of , 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 Monmouthshire ( cy, Sir Fynwy) is a county in the south-east of Wales. The name derives from the historic county of the same name; the modern county covers the eastern three-fifths of the historic county. The largest town is Abergavenny, with ...

, Wales. The estuary is about wide at Aust, and about wide between Cardiff and Weston-super-Mare. It has one of the highest tidal ranges in the world — about . This funnel shape, large tidal range, and the underlying geology of rock, gravel and sand, produce strong tidal streams and high

turbidity Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality. Fluids can ...

, giving the water a notably brown coloration. During the highest tides, rising water is funnelled up the estuary into the Severn bore, a self-reinforcing solitary wave that travels rapidly upstream against the river current. West of the line between Lavernock Point and Sand Point is the

, which in turn discharges into the

Celtic Sea The Celtic Sea ; cy, Y Môr Celtaidd ; kw, An Mor Keltek ; br, Ar Mor Keltiek ; french: La mer Celtique is the area of the Atlantic Ocean off the southern coast of Ireland bounded to the east by Saint George's Channel; other limits includ ...

and the wider

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

. The islands of

Steep Holm Steep Holm ( cy, Ynys Rhonech, ang, Ronech and later ) is an English island lying in the Bristol Channel. The island covers at high tide, expanding to at mean low water. At its highest point it is above mean sea level. Administratively it ...

and

Flat Holm Flat Holm ( cy, Ynys Echni) is a Welsh island lying in the Bristol Channel approximately from Lavernock Point in the Vale of Glamorgan. It includes the most southerly point of Wales. The island has a long history of occupation, dating at lea ...

are located close to that line, in the middle of the estuary. The

Ordnance Survey , nativename_a = , nativename_r = , logo = Ordnance Survey 2015 Logo.svg , logo_width = 240px , logo_caption = , seal = , seal_width = , seal_caption = , picture = , picture_width = , picture_caption = , formed = , preceding1 = , di ...

refers on its published mapping to a section of the estuary seaward of the two estuarine motorway crossings as the ''Mouth of the Severn''.

Conservation and SSSI status

The tidal range results in the estuary having one of the most extensive intertidal wildlife habitats in the UK, comprising mudflats, sandflats, rocky platforms and islands. These form a basis for plant and animal communities typical of extreme physical conditions of liquid mud and tide-swept sand and rock. The estuary is recognised as a wetland area of international importance and is designated as a

Ramsar site A Ramsar site is a wetland site designated to be of international importance under the Ramsar Convention,8 ha (O) *** Permanent 8 ha (P) *** Seasonal Intermittent < 8 ha(Ts) **

Special Protection Area A Special Protection Area (SPA) is a designation under the European Union Directive on the Conservation of Wild Birds. Under the Directive, Member States of the European Union (EU) have a duty to safeguard the habitats of migratory birds and certa ...

(SPA) under the EC Directive on the conservation of Wild Birds. The estuary is recognised as a

Special Area of Conservation A Special Area of Conservation (SAC) is defined in the European Union's Habitats Directive (92/43/EEC), also known as the ''Directive on the Conservation of Natural Habitats and of Wild Fauna and Flora''. They are to protect the 220 habitats and a ...

(SAC) under the EU Habitats Directive. Parts of the estuary have also been designated a

Site of Special Scientific Interest A Site of Special Scientific Interest (SSSI) in Great Britain or an Area of Special Scientific Interest (ASSI) in the Isle of Man and Northern Ireland is a conservation designation denoting a protected area in the United Kingdom and Isle of ...

. The SSSI includes most of the foreshore upstream from Cardiff and

Brean Down Brean Down is a promontory off the coast of Somerset, England, standing high and extending into the Bristol Channel at the eastern end of Bridgwater Bay between Weston-super-Mare and Burnham-on-Sea. Made of Carboniferous Limestone, it is a ...

and most of the upper estuary as far as Sharpness. The Upper Severn Estuary SSSI covers the tidal river between

Purton Purton is a large village and civil parish in Wiltshire, England, about northwest of the centre of Swindon. The parish includes the village of Purton Stoke and the hamlets of Bentham, Hayes Knoll, Purton Common, Restrop, The Fox and Widham. Th ...

and

Frampton on Severn Frampton on Severn is a village and civil parish in Gloucestershire, England. The population is 1,432. Geography The village is approximately south of Gloucester, at . It lies on the east bank of the River Severn, and on the west bank of the ...

.Natural England Upper Severn Estuary SSSI information on citation, map and unit details
/ref> The Severn Estuary SSSI original designation involves the then counties of Somerset, Avon and Gloucestershire in England, and Gwent and South Glamorgan in Wales. The Severn Estuary SSSI designation overlaps individual site designations for separate sites in Avon ( Spring Cove Cliffs,

Middle Hope Sand Point in Somerset, England, is the peninsula stretching out from Middle Hope, an biological and geological Site of Special Scientific Interest. It lies to the north of the village of Kewstoke, and the stretch of coastline called Sand Bay ...

, Portishead Pier to Black Nore,

Aust Cliff Aust Cliff () is a 5.3 hectare geological Site of Special Scientific Interest adjacent to the Severn Estuary, near the village of Aust, South Gloucestershire, notified in 1954. The Severn Bridge crosses the cliff. Its SSSI designation is due to ...

), Gloucestershire ( Purton Passage) and South Glamorgan ( Penarth Coast). The 1976 designation includes two sites previously notified in 1952 (

and

Uphill Cliff Uphill Cliff () is a 19.8 hectare biological Site of Special Scientific Interest near the village of Uphill, North Somerset, although it is in the Avon Area of Search used by English Nature which is based on the 1974-1996 county system. The s ...

). The SSSI forms the major part of a larger area which includes the

Taff Taff may refer to: * River Taff, a large river in Wales * ''Taff'' (TV series), a German tabloid news programme * Trans-Atlantic Fan Fund, an organisation for science fiction fandom People * a demonym for anyone from south Wales * Jerry Taff ( ...

/ Ely Estuary and

Bridgwater Bay Bridgwater Bay is on the Bristol Channel, north of Bridgwater in Somerset, England at the mouth of the River Parrett and the end of the River Parrett Trail. It stretches from Minehead at the southwestern end of the bay to Brean Down in the nor ...

(as well as the Upper Severn Estuary) The Upper Severn Estuary SSSI designation involves the English county of Gloucestershire. The site (Severn Estuary and Upper Severn Estuary) is listed in the 'Forest of Dean Local Plan Review' as a Key Wildlife Site (KWS). Both SSSI citations provide detail of the geological and biological interest and of particular note is the international importance for wintering and wading birds of passage, and of estuarine habits of outstanding ornithological significance. It is stated that the estuary supports over 10% of the British wintering population and is the single most important wintering ground for

dunlin The dunlin (''Calidris alpina'') is a small wader, formerly sometimes separated with the other "stints" in the genus ''Erolia''. The English name is a dialect form of "dunling", first recorded in 1531–1532. It derives from ''dun'', "dull brown ...

, and for significant numbers of

Bewick's swan The tundra swan (''Cygnus columbianus'') is a small swan of the Holarctic. The two taxa within it are usually regarded as conspecific, but are also sometimes split into two species: Bewick's swan (''Cygnus bewickii'') of the Palaearctic and the w ...

s, European

white-fronted geese The greater white-fronted goose (''Anser albifrons'') is a species of goose related to the smaller lesser white-fronted goose (''A. erythropus''). It is named for the patch of white feathers bordering the base of its bill, in fact ''albifrons ...

and

wigeon The wigeons or widgeons are a group of birds, dabbling ducks currently classified in the genus ''Mareca'' along with two other species. There are three extant species of wigeon, in addition to one recently extinct species. Biology There are ...

. Nationally important wintering populations are supported such as gadwall,

shoveller The shovelers or shovellers are four species of dabbling ducks with long, broad spatula-shaped beaks: * Red shoveler, ''Anas platalea'' * Cape shoveler, ''Anas smithii'' * Australasian shoveler, ''Anas rhynchotis'' * Northern shoveler, ''Anas c ...

and

pochard Pochard is a common name used for several species of diving ducks: *Four species in the genus ''Aythya'': ** Common pochard, ''Aythya ferina'' ** Baer's pochard, ''Aythya baeri'' ** Ferruginous pochard, ''Aythya nyroca'' ** Madagascar pochard, '' ...

. There are notably seven species of migratory fish which pass through the estuary in both directions. These include significant numbers of

Atlantic salmon The Atlantic salmon (''Salmo salar'') is a species of ray-finned fish in the family Salmonidae. It is the third largest of the Salmonidae, behind Siberian taimen and Pacific Chinook salmon, growing up to a meter in length. Atlantic salmon are ...

and common eel. At Black Rock,

Portskewett Portskewett ( cy, Porthsgiwed or ''Porthysgewin'') is a village and community (parish) in Monmouthshire, south east Wales. It is located four miles south west of Chepstow and one mile east of Caldicot, in an archaeologically sensitive part of the ...

, a traditional method of fishing for salmon with lave nets is practised. The fishermen promote the fishery as a tourist attraction. In 2021, they reduced their activities in response to pressure from

Natural Resources Wales Natural Resources Wales ( cy, Cyfoeth Naturiol Cymru) is a Welsh Government sponsored body, which became operational from 1 April 2013, when it took over the management of the natural resources of Wales. It was formed from a merger of the Coun ...

to reduce their catch.

Tidal power

left, 300px, Diagram of a plan to harness tidal power on the River Severn circa 1921. Caption from Popular Mechanics Magazine 1921 A huge tidal range and high level of surrounding industry and population have long made the Severn Estuary and

a focus for

tidal energy Tidal power or tidal energy is harnessed by converting energy from tides into useful forms of power, mainly electricity using various methods. Although not yet widely used, tidal energy has the potential for future electricity generation. Ti ...

schemes and ideas. Plans for a

Severn Barrage The Severn Barrage is any of a range of ideas for building a barrage from the English coast to the Welsh coast over the Severn tidal estuary. Ideas for damming or barraging the Severn estuary (and Bristol Channel) have existed since the 19t ...

— running across the Bristol Channel from

near to and south west of

Cardiff Cardiff (; cy, Caerdydd ) is the capital and largest city of Wales. It forms a principal area, officially known as the City and County of Cardiff ( cy, Dinas a Sir Caerdydd, links=no), and the city is the eleventh-largest in the United Kingd ...

near and just south west of

Somerset ( en, All The People of Somerset) , locator_map = , coordinates = , region = South West England , established_date = Ancient , established_by = , preceded_by = , origin = , lord_lieutenant_office =Lord Lieutenant of Somerset , lord_ ...

— would generate a massive 8640 MW when the tide flows, and have been discussed for several decades now. The power generated would come from a lake of with a potential energy depth of . Tidal power only runs for around ten hours a day, but by using the enclosed lake as a reservoir of potential energy more hours of operation could be achieved. Other energy sources, such as wind and solar power, also create electricity at times that do not always match when it is needed. Excess power could be stored by pumping water uphill, as is already done at a variety of other installations in the UK. The UK Government shelved the plans in the late 1980s due largely to cost issues and local environmental concerns. However, this was before recent huge rises in the price of energy, and before

global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...

had started to be taken seriously. In April 2006 the

Welsh Assembly The Senedd (; ), officially known as the Welsh Parliament in English and () in Welsh, is the devolved, unicameral legislature of Wales. A democratically elected body, it makes laws for Wales, agrees certain taxes and scrutinises the Welsh ...

approved the idea of utilising the tidal power, but the RSPB has raised serious concerns about the effect on the mud flats, that have European Environmental protection status, and the UK government Energy Review published later in the year did not endorse the scheme. Opinion is still divided on the benefits of a proposed barrage. John Hutton,

Secretary of State for Business, Enterprise and Regulatory Reform The secretary of state for business, energy and industrial strategy, is a secretary of state in the Government of the United Kingdom, with responsibility for the Department for Business, Energy and Industrial Strategy. The incumbent is a mem ...

, announced a further feasibility study on 25 September 2007. The

Severn Tidal Power Feasibility Study Severn Tidal Power Feasibility Study is the name of a Her Majesty's Government, UK Government feasibility study into a tidal power project looking at the possibility of using the huge tidal range in the Severn Estuary and Bristol Channel to genera ...

was launched in January 2008 to assess all tidal range technologies (including barrages, lagoons and others). The study will look at the costs, benefits and impacts of a Severn tidal power scheme and will help Government decide whether it could or could not support such a scheme. The Severn Estuary has the potential to generate more renewable electricity than all other UK estuaries. If harnessed, it could create up to 5% of the UK's electricity, contributing significantly to UK climate change goals as well as European Union renewable energy targets. The proposal for a

hydro-electric Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined an ...

barrier to generate 8.6 GW and meet five percent of Britain's power needs, is being opposed by some environmental groups.

Severn Estuary Partnership

The Severn Estuary Partnership (SEP) was set up in 1995 as an independent initiative to focus the activities of local government, statutory authorities and interested parties such as farmers and fisherman. Its stated aim is ''To bring together all those involved in the development, management and use of the Estuary within a framework which encourages the integration of their interests and responsibilities to achieve common objectives''. In 2001 SEP published the ''Strategy for the Severn Estuary'', which sets out a plan for the management of the estuary. SEP uses a geographically extended definition of the Severn Estuary, beginning at the tidal limit of the River Severn in

and ending at a line drawn between Hurlestone Point near

Minehead Minehead is a coastal town and civil parish in Somerset, England. It lies on the south bank of the Bristol Channel, north-west of the county town of Taunton, from the boundary with the county of Devon and in proximity of the Exmoor National P ...

and

Nash Point Nash Point ( cy, Trwyn yr As) is a headland and beach in the Monknash Coast of the Vale of Glamorgan in south Wales, about a mile from Marcross. It is a popular location for ramblers and hiking along the cliffs to Llantwit Major beach. The l ...

in the

Vale of Glamorgan The Vale of Glamorgan ( cy, Bro Morgannwg ), often referred to as The Vale, is a county borough in the south-east of Wales. It borders Bridgend County Borough to the west, Cardiff to the east, Rhondda Cynon Taf to the north, and the Bristol C ...

Archaeology

The archaeology of the Severn Estuary is richly varied and of considerable importance, reflecting both the varied nature of the topography and the importance of the river for both fishing and as a maritime waterway. The archaeological resource within the estuary is under threat from natural processes such as

coastal erosion Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. The landward ...

, exacerbated by the high tidal range and strong tidal currents, and from threats such as ongoing development pressure along the shoreline, marine aggregates extraction and new coastal defensive and realignment measures as well as proposed major infrastructure projects. An archaeological aerial survey report of the archaeology on the English side is available to view and download from the reference link.

References

External links

The Severn Estuary Partnership

Natural England
(SSSI information) {{authority control Bristol Channel River Severn Sites of Special Scientific Interest in Avon Coast of Cardiff Sites of Special Scientific Interest in Gloucestershire Coast of Monmouthshire Sites of Special Scientific Interest in Monmouthshire Coast of Newport, Wales Sites of Special Scientific Interest in Newport Coast of the Vale of Glamorgan Estuaries of England Ramsar sites in England Ramsar sites in Wales England–Wales border Sites of Special Scientific Interest notified in 1976 Wetland Sites of Special Scientific Interest Natural regions of England Estuaries of Wales Bodies of water of Monmouthshire Bodies of water of Newport, Wales Bodies of water of the Vale of Glamorgan