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). [1] [2] 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.
Definitions of the limits of the Severn Estuary vary. In pre-modern times the area was commonly referred to as the River Severn, or the Severn Sea. Today, at the upstream boundary, the normal tidal limit of the river is at Maisemore weir (on the West Channel) and Llanthony Weir (on the East Channel), close to Gloucester Docks, although exceptionally high tides can overtop these weirs. [3]
Downstream, the International Hydrographic Organization places the boundary between the estuary and the open sea of the Bristol Channel at a line between Sand Point, North Somerset (north of Weston-super-Mare) and Lavernock Point (south of Penarth in south Wales), at which point it is over 8 miles (13 km) wide. [4] This definition is used by the Severn Estuary Partnership [5] and Visit England. [6]
A narrower definition adopted for navigation purposes by some charts includes only the area downstream of the Second Severn Crossing near Severn Beach, South Gloucestershire. [7] 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 Severn Bridge.
On the north-west (Welsh) side, the rivers Wye and Usk flow into the estuary, and on the south-east (English) side, the River Avon joins at Avonmouth. West of the Wye, the estuary forms the boundary between Wales and England. 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.
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. It has one of the highest tidal ranges in the world — about 50 feet (15 m). [8] [9] This funnel shape, large tidal range, and the underlying geology of rock, gravel and sand, produce strong tidal streams and high turbidity, 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. [10]
West of the line between Lavernock Point and Sand Point is the Bristol Channel, which in turn discharges into the Celtic Sea and the wider Atlantic Ocean. The islands of Steep Holm and Flat Holm are located close to that line, in the middle of the estuary. The Ordnance Survey refers on its published mapping to a section of the estuary seaward of the two estuarine motorway crossings as the Mouth of the Severn. [11]
| Site of Special Scientific Interest | |
  Location near Somerset | |
| Location | Gloucestershire |
|---|---|
| Grid reference | ST480830 |
| Coordinates | 51°27′42″N2°59′47″W / 51.4617°N 2.9965°W |
| Interest | Biological/Geological |
| Area | 15950 hectare |
| Notification | 1976 (Brean Down and Uphill Cliff 1952) |
| Natural England website | |
| Site of Special Scientific Interest | |
| Location | Gloucestershire |
|---|---|
| Grid reference | SO720060 |
| Interest | Biological/Geological |
| Area | 1436.8 hectare |
| Notification | 1954 |
| Natural England website | |
| Designations | |
|---|---|
| Official name | Severn Estuary |
| Designated | 5 January 1976 |
| Reference no. | 67 [12] |
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. [13] [14] The estuary is recognised as a Special Protection Area (SPA) under the EC Directive on the conservation of Wild Birds. [15] [16] The estuary is recognised as a Special Area of Conservation (SAC) under the EU Habitats Directive. [17] [18]
Parts of the estuary have also been designated a Site of Special Scientific Interest. The SSSI includes most of the foreshore upstream from Cardiff and Brean Down and most of the upper estuary as far as Sharpness. [1] The Upper Severn Estuary SSSI covers the tidal river between Purton and Frampton on Severn. [19]
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, Portishead Pier to Black Nore, Aust Cliff), Gloucestershire (Purton Passage) and South Glamorgan (Penarth Coast). The 1976 designation includes two sites previously notified in 1952 (Brean Down and Uphill Cliff). The SSSI forms the major part of a larger area which includes the Taff/Ely Estuary and Bridgwater Bay (as well as the Upper Severn Estuary) [1]
The Upper Severn Estuary SSSI designation involves the English county of Gloucestershire. [19] The site (Severn Estuary and Upper Severn Estuary) is listed in the 'Forest of Dean Local Plan Review' as a Key Wildlife Site (KWS). [20]
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, [1] and of estuarine habits of outstanding ornithological significance. [19] It is stated that the estuary supports over 10% of the British wintering population and is the single most important wintering ground for dunlin, [1] and for significant numbers of Bewick's swans, European white-fronted geese and wigeon. [19] Nationally important wintering populations are supported such as gadwall, shoveller and pochard. [19]
There are notably seven species of migratory fish which pass through the estuary in both directions. These include significant numbers of Atlantic salmon and common eel. [1] At Black Rock, Portskewett, 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 to reduce their catch. [21]
A huge tidal range and high level of surrounding industry and population have long made the Severn Estuary and Bristol Channel a focus for tidal energy schemes and ideas. Plans for a Severn Barrage — running 16 km (9.9 mi) across the Bristol Channel from Lavernock Point near to and south west of Cardiff to Brean Down near and just south west of Weston-super-Mare in Somerset — 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 185 square miles (479 km2) with a potential energy depth of 14 metres (46 ft). 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 had started to be taken seriously. In April 2006 the Welsh Assembly 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. [22]
Opinion is still divided on the benefits of a proposed barrage. John Hutton, Secretary of State for Business, Enterprise and Regulatory Reform, announced a further feasibility study on 25 September 2007. The Severn Tidal Power Feasibility Study 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. [23] The proposal for a hydro-electric barrier to generate 8.6 GW and meet five percent of Britain's power needs, is being opposed by some environmental groups. [24] [25]
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. [26] In 2001 SEP published the Strategy for the Severn Estuary, which sets out a plan for the management of the estuary. [26]
SEP uses a geographically extended definition of the Severn Estuary, beginning at the tidal limit of the River Severn in Gloucester and ending at a line drawn between Hurlestone Point near Minehead and Nash Point in the Vale of Glamorgan.
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, 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. [27] An archaeological aerial survey report of the archaeology on the English side is available to view and download from the reference link. [28]
The River Severn, at 220 miles (354 km) long, is the longest river in Great Britain. It is also the river with the most voluminous flow of water by far in all of England and Wales, with an average flow rate of 107 m3/s (3,800 cu ft/s) at Apperley, Gloucestershire. It rises in the Cambrian Mountains in mid Wales, at an altitude of 2,001 feet (610 m), on the Plynlimon massif, which lies close to the Ceredigion/Powys border near Llanidloes. The river then flows through Shropshire, Worcestershire and Gloucestershire. The county towns of Shrewsbury, Worcester and Gloucester lie on its course.
The River Avon is a river in the southwest of England. To distinguish it from a number of other rivers of the same name, it is often called the Bristol Avon. The name 'Avon' is loaned from an ancestor of the Welsh word afon, meaning 'river'.
Bridgwater Bay is on the Bristol Channel, 5 kilometres (3.1 mi) 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 north. The area consists of large areas of mudflats, saltmarsh, sandflats and shingle ridges, some of which are vegetated. It has been designated as a Site of Special Scientific Interest (SSSI) covering an area of 3,574.1 hectares since 1989, and is designated as a wetland of international importance under the Ramsar Convention. The risks to wildlife are highlighted in the local Oil Spill Contingency Plan.
The Bristol Channel is a major inlet in the island of Great Britain, separating South Wales and South West England. It extends from the smaller Severn Estuary of the River Severn to the North Atlantic Ocean. It takes its name from the English city and port of Bristol.
Cardiff Bay Barrage lies across the mouth of Cardiff Bay, Wales between Queen Alexandra Dock and Penarth Head. It was one of the largest civil engineering projects in Europe during construction in the 1990s.
Penarth is a town and community in the Vale of Glamorgan, Wales, approximately 3 miles (4.8 km) south of Cardiff city centre on the west shore of the Severn Estuary at the southern end of Cardiff Bay.
Flat Holm is a Welsh island lying in the Bristol Channel approximately 6 km (4 mi) from Lavernock Point in the Vale of Glamorgan. It includes the most southerly point of Wales.
Lavernock is a hamlet in the Vale of Glamorgan in Wales, lying on the coast 7 miles (11 km) south of Cardiff between Penarth and Sully, and overlooking the Bristol Channel.
Brean Down is a promontory off the coast of Somerset, England, standing 318 feet (97 m) high and extending 1+1⁄2 miles into the Bristol Channel at the eastern end of Bridgwater Bay between Weston-super-Mare and Burnham-on-Sea.
Walmore Common is a 57.78-hectare (142.8-acre) nature reserve on the flood-plain of the River Severn, west of the city of Gloucester in England and north of the village of Chaxhill. It was notified as a biological Site of Special Scientific Interest in 1966. The site is listed in the 'Forest of Dean Local Plan Review' as a Key Wildlife Site (KWS).
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 have existed since the 19th century. The building of such a barrage would constitute an engineering project comparable with some of the world's biggest. The purposes of such a project have typically been one or several of: transport links, flood protection, harbour creation, or tidal power generation. In recent decades it is the latter that has grown to be the primary focus for barrage ideas, and the others are now seen as useful side-effects. Following the Severn Tidal Power Feasibility Study (2008–10), the British government concluded that there was no strategic case for building a barrage but to continue to investigate emerging technologies. In June 2013 the Energy and Climate Change Select Committee published its findings after an eight-month study of the arguments for and against the Barrage. MPs said the case for the barrage was unproven. They were not convinced the economic case was strong enough and said the developer, Hafren Power, had failed to answer serious environmental and economic concerns.
Lavernock Battery was built at Lavernock Point, Wales on the recommendations of the 1860 Royal Commission during the late 1860s to protect the ports of the Severn Estuary. It was replaced by a new anti-aircraft battery during World War II that was equipped with four heavy anti-aircraft guns.
Berkeley nuclear power station is a former Magnox nuclear power station situated on the bank of the River Severn in Gloucestershire, England. The ongoing decommissioning process is being managed by Nuclear Decommissioning Authority subsidiary Magnox Ltd.
Severn Tidal Power Feasibility Study is the name of a 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 generate electricity.
Portbury Ashlands which is now known as Portbury Wharf Nature Reserve is a nature reserve between Portishead and the Royal Portbury Dock in Somerset, England. It was formed from the redevelopment of the area of Portishead formerly occupied by two power stations. To the east of the harbour, an area known as "the Ashlands" was used for over 50 years to get rid of power station waste which was dumped into lagoons on the site.
A tidal barrage is a dam-like structure used to capture the energy from masses of water moving in and out of a bay or river due to tidal forces.
Pîl is a Welsh placename element. The name is defined as the tidal reach of a waterway, suitable as a harbour, and is common along the Bristol Channel and Severn Estuary. The highly localised distribution suggests it may have been part of a common maritime culture on the waterways within the tidal reach of the Severn Sea.
The coastline of Wales extends from the English border at Chepstow westwards to Pembrokeshire then north to Anglesey and back eastwards to the English border once again near Flint. Its character is determined by multiple factors, including the local geology and geological processes active during and subsequent to the last ice age, its relative exposure to or shelter from waves, tidal variation and the history of human settlement and development which varies considerably from one place to another. The majority of the coast east of Cardiff in the south, and of Llandudno in the north, is flat whilst that to the west is more typically backed by cliffs. The cliffs are a mix of sandstones, shales and limestones, the erosion of which provides material for beach deposits. Of the twenty-two principal areas which deliver local government in Wales, sixteen have a coastline, though that of Powys consists only of a short section of tidal river some distance from the open sea. Its length has been estimated at 1,680 miles (2,700 km).
51.4617° N, 2.9965° W Severn Estuary, Coordinates
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