Bristol Channel

The Bristol Channel (Welsh: Môr Hafren) 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 (Welsh: Afon Hafren) 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 Welsh: Môr Hafren and Cornish: Mor Havren.[1]

Bristol channel detailed map
The Bristol Channel
Sunrise viewed from Minehead, showing Steep Holm and Brean Down


The International Hydrographic Organisation now defines the western limit of the Bristol Channel as "a line joining Hartland Point in Devon (51°01′N 4°32′W / 51.017°N 4.533°W) to St. Govan's Head in Pembrokeshire (51°36′N 4°55′W / 51.600°N 4.917°W)". 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.[2]

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, more specifically the Celtic Sea.

Within its officially defined limits, the Bristol Channel extends for some 75 miles (121 km) from west to east, but 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.[3] The Severn Estuary and most of the embayments around the channel are less than 10 m in depth. Within the channel, however, there is an E-W trending valley 20 to 30 m in depth that is considered to have been formed by fluvial run-off during Pleistocene phases of lower sea level.[4] 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 Welsh coast are the OBel Sands, an extensive area of sand waves up to 19 m high, covering an area of over 1,000 km².[5]


Bristol Channel from Porthkerry
The channel as seen from Barry, Wales
The Bristol Channel coast at Ilfracombe, North Devon, looking west towards Lee Bay, with Lundy in the distance

The Bristol Channel is an important area for wildlife, in particular waders, and has protected areas, including national nature reserves such as Bridgwater Bay at the mouth of the River Parrett. At low tide large parts of the channel become mud flats due to the tidal range of 43 feet (13 m),[6] second only to the Bay of Fundy in Eastern Canada.[7][8] Development schemes have been proposed along the channel, including an airport and a tidal barrier for electricity generation, but conservation issues have so far managed to block such schemes.

The largest islands in the Bristol Channel are Lundy, Steep Holm and Flat Holm. The islands and headlands provide some shelter for the upper reaches of the channel from storms. These islands are mostly uninhabited and protected as nature reserves, and are home to some unique wild flower species. In 1971 a proposal was made by the Lundy Field Society to establish a marine reserve. Provision for the establishment of statutory Marine Nature Reserves was included in the Wildlife and Countryside Act 1981, and on 21 November 1986 the Secretary of State for the Environment announced the designation of a statutory reserve at Lundy.[9] There is an outstanding variety of marine habitats and wildlife, and a large number of rare and unusual species in the waters around Lundy, including some species of seaweed, branching sponges, sea fans and cup corals.[10]

The Bristol Channel has some extensive and popular beaches and spectacular scenery, particularly on the coasts of Exmoor and Bideford Bay in North Devon and the Vale of Glamorgan and Gower Peninsula on the Glamorgan coast. The western stretch of Exmoor boasts Hangman cliffs, the highest cliffs in mainland Britain, culminating near Combe Martin in the "Great Hangman", a 1,043 ft (318 m) 'hog-backed' hill with a cliff-face of 820 ft (250 m); its sister cliff the "Little Hangman" has a cliff-face of 716 ft (218 m). On the Gower Peninsula, at its western extremity is the Worms Head, a headland of carboniferous limestone which is approachable on foot at low tide only. The beaches of Gower (at Rhossili, for example) and North Devon, such as Croyde and Woolacombe, win awards for their water quality and setting, as well as being renowned for surfing. In 2004, The Times "Travel" magazine selected Barafundle Bay in Pembrokeshire as one of the twelve best beaches in the world. In 2007, Oxwich Bay made the same magazine's Top 12 best beaches in the world list, and was also selected as Britain's best beach for 2007.

Coastal cities and towns

Llantwit Major Beach Bristol Channel
The Bristol Channel looking south from Llantwit Major near Barry on the Glamorgan coast
Bristol channel landsat7
Satellite view of the Bristol Channel

The city of Swansea is the largest settlement on the Welsh coast of the Bristol Channel. Other major built-up areas include Barry (including Barry Island), Port Talbot and Llanelli. Smaller resort towns include Porthcawl, Mumbles, Saundersfoot and Tenby. The cities of Cardiff and Newport adjoin the Severn estuary, but lie upstream of the Bristol Channel itself.

On the English side, the resort towns of Weston-super-Mare, Burnham-on-Sea, Watchet, Minehead and Ilfracombe are located on the Bristol Channel. Barnstaple and Bideford are sited on estuaries opening onto Bideford Bay, at the westernmost end of the Bristol Channel. Just upstream of the official eastern limit of the Channel, adjoining the Severn estuary, is the city of Bristol, originally established on the River Avon but now with docks on the Severn estuary, which is one of the most important ports in Britain. It gives its name to the Channel, which forms its seaward approach.


There are no road or rail crossings of the Bristol Channel so direct crossings are necessarily made by sea or air, or less directly by the road and rail crossings of the Severn estuary. The Channel can be a hazardous area of water because of its strong tides and the rarity of havens on the north Devon and Somerset coasts that can be entered in all states of the tide. Because of the treacherous waters, pilotage is an essential service for shipping. A specialised style of sailing boat, the Bristol Channel Pilot Cutter, developed in the area.

Paddle steamers

P and A Campbell of Bristol were the main operators of pleasure craft, particularly paddle steamers, from the mid-19th century to the late 1970s, together with the Barry Railway Company. These served harbours along both coasts, such as Ilfracombe and Weston-super-Mare.

This tradition is continued each summer by the PS Waverley, the last seagoing paddle steamer in the world, built in 1947. The steamer provides pleasure trips between the Welsh and English coasts and to the islands of the channel. Trips are also offered on the MV Balmoral, also owned by Waverley Excursions.

Marine rescue services

The Burnham-on-Sea Area Rescue Boat (BARB)[2] uses a hovercraft to rescue people from the treacherous mud flats on that part of the coast. A hovercraft was recently tested to determine the feasibility of setting up a similar rescue service in Weston-super-Mare. There are also RNLI lifeboats stationed along both sides of the Channel. In the Severn Estuary, in-shore rescue is provided by two independent lifeboat trusts, the Severn Area Rescue Association (SARA) and the Portishead and Bristol Lifeboat Trust.[11]

Renewable energy

The Bristol Channel and Severn Estuary have the potential to generate more renewable electricity than any other in the UK. It has been stated that it would contribute significantly to UK climate change goals and European Union renewable energy targets. Earlier studies of a possible Severn Barrage included estimates of bed load transport of sand and gravel by tidal ebb and flood that would be interrupted if a solid dam were built across the Channel.[12] More recently, the Severn Tidal Power Feasibility Study was launched in 2008 by the British Government to assess all tidal range technologies, including barrages, lagoons and others.[13] 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. Some of the options being looked at may include a road crossing downstream of the existing crossings of the estuary.

1607 flood

On 30 January 1607 (New style) thousands of people were drowned, houses and villages swept away, farmland inundated and flocks destroyed when a flood hit the shores of the Channel. The devastation was particularly bad on the Welsh side, from Laugharne in Carmarthenshire to above Chepstow on the English border. Cardiff was the most badly affected town. There remain plaques up to 8 ft (2.4 m) above sea level to show how high the waters rose on the sides of the surviving churches. It was commemorated in a contemporary pamphlet "God's warning to the people of England by the great overflowing of the waters or floods."

The cause of the flood is uncertain and disputed. It had long been believed that the floods were caused by a combination of meteorological extremes and tidal peaks, but research published in 2002 showed some evidence of a tsunami in the Channel.[14] Although some evidence from the time describes events similar to a tsunami, there are also similarities to descriptions of the 1953 floods in East Anglia, which were caused by a storm surge. It has been shown that the tide and weather at the time were capable of generating such a surge.[15]


In 1835 John Ashley was on the shore at Clevedon with his son who asked him how the people on Flat Holm could go to church. For the next three months Ashley voluntarily ministered to the population of the island. From there he recognised the needs of the seafarers on the four hundred sailing vessels in the Bristol Channel and created the Bristol Channel Mission. He raised funds and in 1839 a specially designed mission cutter was built with a main cabin which could be converted into a chapel for 100 people, this later became first initiative of the Mission to Seafarers.[16]



Much of the coastline at the western end of the Bristol Channel faces west towards the Atlantic Ocean meaning that a combination of an off-shore (east) wind and a generous Atlantic swell produces excellent surf along the beaches. The heritage coasts of the Vale of Glamorgan, Bideford Bay and Gower are, along with the Atlantic coasts of Pembrokeshire and Cornwall, the key areas for surfing in the whole of Britain. Although slightly overshadowed by the Atlantic coasts of North Cornwall and West Pembrokeshire, both Gower and Bideford Bay nevertheless have several superb breaks—notably Croyde in Bideford Bay and Langland Bay on Gower—and surfing in Gower and Bideford Bay is enhanced by the golden beaches, clean blue waters, excellent water quality and good facilities close by to the main surf breaks.

Windsurfing across the channel

The first known crossing of the Bristol Channel (from Swansea to Woody Bay, near Lynton, Devon) by a windsurfer was Adam Cowles in April 2006,[17] apparently accidentally. Other windsurfers have reported making the crossing as a training exercise (Hugh Sim Williams[18]) or as part of a windsurf around Britain (e.g. Jono Dunnett [19]). The coastguard has stated that windsurf crossings of the channel are dangerous and should not be attempted without appropriate preparations.[17]


The high quality of the landscape of much of both coasts of the Bristol Channel means that they are popular destinations for walkers. Sections of two national trails; the South West Coast Path and the Pembrokeshire Coast Path follow these shores, and the West Somerset Coast Path extends eastwards from the South West Coast Path to the mouth of the River Parrett. A continuous coastal path, the Wales Coast Path, was opened in May 2012 along the entire Welsh shore under the auspices of the Countryside Council for Wales.

Swimming records

First person to swim across the Bristol Channel

The first person to swim across the Bristol Channel was Kathleen Thomas, a 21-year-old woman from Penarth who swam to Weston-super-Mare on 5 September 1927.[20] She completed the swim, nominally 11 miles but equivalent to 22 miles because of tidal flows, in 7 hours 20 minutes. In 2007 the achievement was marked by a plaque in seafront in Penarth.[21]

Youngest person to swim across the Bristol Channel

In 1929 Edith Parnell, a 16-year-old schoolgirl, emulated Kathleen Thomas's swim from Penarth to Weston-super-Mare in 10 hours 15 minutes.[20] Edith later became the first wife of Hugh Cudlipp the Welsh journalist and newspaper editor.[21][22]

Ilfracombe to Swansea

The first person to swim the 30.5 nautical miles (56.5 km; 35.1 mi) from Ilfracombe to Swansea was Gethin Jones, who achieved the record on 13 September 2009, taking nearly 22 hours.[23]

Penarth to Clevedon

The youngest person to swim the Bristol Channel from Penarth to Clevedon is Gary Carpenter who at age 17 on August bank holiday 2007, swam the channel in 5 hours 35 minutes making him the youngest and fastest swimmer of the Bristol Channel. Gary Carpenter's coach Steve Price was the first ever person to swim from Penarth to Clevedon back in 1990.[24]


  1. ^ The sixteenth-century geographer, Roger Barlow, defined the ‘see called severne’ as all those waters east of the Scilly Isles ‘betwene the principlitie of wales and englande’: E. G. R. Taylor (ed.), A Brief Summe of Geographie, by Roger Barlow (Abingdon, 2016), p. 32.
  2. ^ "Limits of Oceans and Seas, 3rd edition + corrections" (PDF). International Hydrographic Organization. 1971. p. 42 [corrections to page 13]. Retrieved 6 February 2010.
  3. ^ Steers, J.A., 1964. The Coastline of England and Wales. Cambridge Univ. Press, Cambridge, 750 pp.
  4. ^ Collins, M.B., 1987. Sediment transport in the Bristol Channel: a review. Proceedings of the Geological Association 98, 367-383.
  5. ^ James, J.W.C., Mackie, A.S.Y., Rees, E.I.S., Darbyshire, T., 2012. Ch. 12: Sand wave field: The OBel Sands, Bristol Channel, U.K. , in: Harris, P.T., Baker, E.K. (Eds.), Seafloor geomorphology as benthic habitat: GeoHAB Atlas of seafloor geomorphic features and benthic habitats. Elsevier, Amsterdam, pp. 227-240.
  6. ^ "Severn Estuary Barrage". UK Environment Agency. 31 May 2006. Archived from the original (PDF) on 30 September 2007. Retrieved 3 September 2007.
  7. ^ Chan, Marjorie A.; Archer, Allen William (2003). Extreme Depositional Environments: Mega End Members in Geologic Time. Boulder, Colorado: Geological Society of America. p. 151. ISBN 0-8137-2370-1.
  8. ^ "Coast: Bristol Channel". BBC. Retrieved 27 August 2007.
  9. ^ "Lundy Island Marine Nature Reserve". Archived from the original on 12 September 2007. Retrieved 5 September 2007.
  10. ^ "Lundy Marine Conservation Zone". Lundy Field Society. Retrieved 5 August 2017.
  11. ^ "RNLI Portishead : Home".
  12. ^ Harris, P.T., Collins, M.B., 1988. Estimation of annual bedload flux in a macrotidal estuary, Bristol Channel, U. K. Marine Geology 83, 237-252.
  13. ^ "Severn Tidal Power" (PDF). Welsh Assembly Government. Retrieved 19 November 2016.
  14. ^ Haslett, Simon K.; Edward A. Bryant (2004). "The AD 1607 coastal flood in the bristol channel and severn estuary: historical records from Devon and Cornwall (UK)". Archaeology in the Severn Estuary. 15: 81–89.
  15. ^ Horsburgh, K.J. and M. Horritt (2006) The Bristol Channel floods of 1607 – reconstruction and analysis. Weather, 61(10), 272-277.
  16. ^ Farr, Grahame (1954). Somerset Harbours. London: Christopher Johnson. p. 49.
  17. ^ a b "Windsurfer's accidental crossing". 13 April 2006 – via
  18. ^ Bristol, University of. "2006: Medical student's Olympic dream - News - University of Bristol".
  19. ^ "Jono Dunnett".
  20. ^ a b Martha De Lacey (5 February 2013). "'Mere women' who did the impossible". Daily Mail.
  21. ^ a b Catherine Jones (2012). Wonder Girls. BookOxygen. Simon & Schuster. ISBN 1849838828. Archived from the original on 6 June 2013.
  22. ^ "Getty Images".
  23. ^ Peregrine, Chris (25 July 2016). "Swansea doctor becomes first woman to complete 24 mile swim from Ilfracombe to Swansea". South Wales Evening Post. Retrieved 19 November 2016.
  24. ^ Western Daily Press, 27 August 2008 - Surprise at pier for Channel swimmer Gary [1]

Coordinates: 51°18′N 3°37′W / 51.300°N 3.617°W


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 Estuary. Strategically the area has been and remains an important part of the region's maritime economy particularly for larger vessels for the unloading and exporting of heavier goods as well as in industry including warehousing, light industry, electrical power and sanitation. The geographically compact settlement was established as a parish independent from Shirehampton in 1893 and its first church, completed in 1934, was bombed in World War II by bombers of the Luftwaffe in one of latter of the six major raids which formed the Bristol Blitz, in 1941. The area contains a junction of and is connected to the south by the M5 motorway and other roads, railway tracks and paths to the north, south-east and east.

The council ward of Avonmouth and Lawrence Weston is as drawn a simplified name as it includes Shirehampton and the western end of Lawrence Weston.

Bristol Channel floods, 1607

The Bristol Channel floods, 30 January 1607, drowned many people and destroyed a large amount of farmland and livestock. Recent research has suggested that the cause may have been a tsunami.

Bristol Channel pilot cutter

A Bristol Channel pilot cutter is a specialised sailing boat the style and design of which is derived from the single-masted cutter. Based upon bulkier, less nimble, fishing boats but modified for use in the strong tides, winds, currents and coastline of the Bristol Channel its purpose was to quickly ferry local maritime pilots to and from large ships to assist in safe navigation into or out of any of the port cities in the Channel. The speed and manoeuvrability of the cutters allowed a minimal crew, in almost any weather, to quickly arrive at and easily lie alongside larger ships for easy and safe transfer of pilots. The craft was also equipped to stay 'on station' for days or even weeks, awaiting arrivals just outside the channel.

The design has been described as the best sailing boat design ever, for being both high speed, highly manoeuvrable and yet easy to handle by just two crew.

With the advent of steam engines and vessels made out of metal, the wooden sailing cutters fell out of use and many were sold and later lost. Only a relative handful of the many Bristol Channel pilot cutters survive today.

Burnham-on-Sea Round Tower

The Round Tower was a lighthouse in Burnham-on-Sea, Somerset, England. It is now a private dwelling.

Burnham-on-Sea is notable for its beach and mudflats, which are characteristic of Bridgwater Bay and the rest of the Bristol Channel where the tide can recede for over 1.5 miles (2.4 km). Burnham is close to the estuary of the River Parrett where it flows into the Bristol Channel, which has the second highest tidal range in the world of 15 metres (49 ft), second only to Bay of Fundy in Eastern Canada.

The constantly shifting sands have always been a significant risk to shipping in the area.


Dyfed (Welsh pronunciation: ['dəvɛd]) is a preserved county of Wales. It was created on 1 April 1974, as an amalgamation of the three pre-existing counties of Cardiganshire, Carmarthenshire and Pembrokeshire. It was abolished twenty-two years later, on 1 April 1996, when the three original counties were reinstated, Cardiganshire being renamed Ceredigion the following day. The name "Dyfed" is retained for certain ceremonial and other purposes. It is a mostly rural county in southwestern Wales with a coastline on the Irish Sea and the Bristol Channel.

Flat Holm

Flat Holm (Welsh: Ynys Echni) is a limestone 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.

The island has a long history of occupation, dating at least from Anglo-Saxon and Viking age. Religious uses include visits by disciples of Saint Cadoc in the 6th century, and in 1835 it was the site of the foundation of the Bristol Channel Mission, which later became the Mission to Seafarers. A sanatorium for cholera patients was built in 1896 as the isolation hospital for the port of Cardiff. Guglielmo Marconi transmitted the first wireless signals over open sea from Flat Holm to Lavernock. Because of frequent shipwrecks a lighthouse was built on the island, which was replaced by a Trinity House lighthouse in 1737. Because of its strategic position on the approaches to Bristol and Cardiff a series of gun emplacements, known as Flat Holm Battery, were built in the 1860s as part of a line of defences, known as Palmerston Forts. On the outbreak of World War II, the island was rearmed.

It forms part of the City and County of Cardiff and is now managed by Cardiff Council's Flat Holm Project Team and designated as a Local Nature Reserve, Site of Special Scientific Interest and a Special Protection Area, because of the maritime grassland and rare plants such as rock sea-lavender (Limonium binervosum) and wild leek (Allium ampeloprasum). The island also has significant breeding colonies of lesser black-backed gulls (Larus fuscus), herring gulls (Larus argentatus) and great black-backed gulls (Larus marinus). It is also home to slowworms (Anguis fragilis) with larger than usual blue markings.

Hartland, Devon

The village of Hartland, whose parish incorporates the hamlet of Stoke to the west and the village of Meddon in the south, is the most north-westerly settlement in the county of Devon, England.

Now a large village which acts as a centre for a rural neighbourhood and has minor tourist traffic, until Tudor times Hartland was an important port. It lies close to the promontory of Hartland Point, where the coast of Devon turns from facing north into the Bristol Channel to face west into the Atlantic Ocean. There is an important lighthouse on the point. The town's harbour, Hartland Quay, is to the south of the point: the quay was originally built in the late 16th century but was swept away in 1887. The high tower of the Church of Saint Nectan in Stoke remains a significant landmark for ships in the Bristol Channel. The appropriate electoral ward is called Hartland and Bradworthy. Its population at the 2011 census was 3,019.

Hartland Point Lighthouse

Hartland Point Lighthouse is a Grade II listed building at Hartland Point, Devon, England. The point marks the western limit (on the English side) of the Bristol Channel with the Atlantic Ocean continuing to the west.

Trinity House, the lighthouse authority for England and Wales, have a lighthouse on the tip of the peninsula.


Lavernock (Welsh: Larnog) 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.

Lox Yeo River

The Lox Yeo is a short river in North Somerset, England. It rises at Winscombe and flows south west for about 6 kilometres (4 mi) to join the River Axe near Loxton.

The river flows through a gap in the Mendip Hills between Crook Peak and Bleadon Hill, through which the M5 motorway now runs.

The river was once known simply as the Lox. The name appears to be of Celtic origin, and means either "winding stream" or "bright one".

MV Balmoral (1949)

MV Balmoral is a vintage excursion ship owned by MV Balmoral Fund Ltd., a preservation charity. Her principal area of operation is the Bristol Channel, although she also operates day excursions to other parts of the United Kingdom. The Balmoral is included on the National Historic Ships register as part of the National Historic Fleet.

Porlock Bay

Porlock Bay is on the Bristol Channel, between Hurlstone Point and Porlock Weir in Somerset, England.

The coastline includes shingle ridges, salt marshes and a submerged forest. In 1052 the Saxon king, Harold, landed at Porlock Bay from Ireland, and burnt the town before marching on London.Much of the coastline is under the care of the National Trust, and the coastline forms part of the South West Coast Path.

Port of Bristol

The Port of Bristol comprises the commercial, and former commercial, docks situated in and near the city of Bristol in England. The Port of Bristol Authority was the commercial title of the Bristol City, Avonmouth, Portishead and Royal Portbury Docks when they were operated by Bristol City Council, which ceased trade when the Avonmouth and Royal Portbury Docks were leased to The Bristol Port Company in 1991.

River Aller

The River Aller is a small river on Exmoor in Somerset, England.

It rises as several small streams around Tivington and Huntscott and flows through the Holnicote Estate passing Holnicote and through Allerford, where it passes under a packhorse bridge of medieval origin. It then joins the River Horner, which flows into Porlock Bay near Hurlstone Point on the Bristol Channel.Because of the surrounding geology the area has been at risk of flooding. To help manage this risk telemetry monitoring of flows and a siren warning system have been proposed.

River Axe (Bristol Channel)

The River Axe is a river in South West England. The river is formed by water entering swallets in the limestone and rises from the ground at Wookey Hole Caves in the Mendip Hills in Somerset, and runs through a V-shaped valley. The geology of the area is limestone and the water reaches Wookey Hole in a series of underground channels that have eroded through the soluble limestone. The river mouth is in Weston Bay on the Bristol Channel.

The river was navigable from the middle ages until 1915, and used for international trade.

River Horner

The River Horner, also known as Horner Water, rises near Luccombe on Exmoor, Somerset, and flows past Porlock into Porlock Bay near Hurlstone Point on the Bristol Channel.

Severn Estuary

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

Steep Holm

Steep Holm (Welsh: Ynys Rhonech, Old English: Ronech and later Steopanreolice) is an English island lying in the Bristol Channel. The island covers 48.87 acres (19.78 ha) at high tide, expanding to 63.26 acres (25.60 ha) at mean low water. At its highest point it is 78 metres (256 ft) above mean sea level. It lies within the historic boundaries of Somerset and administratively forms part of North Somerset. Between 1 April 1974 and 1 April 1996 it was administered as part of Avon. Nearby is Flat Holm island (Welsh: Ynys Echni), part of Wales.

The Carboniferous Limestone island rises to about 200 feet (61 m) and serves as a wind and wave break, sheltering the upper reaches of the Bristol Channel. The island is now uninhabited, with the exception of the wardens. It is protected as a nature reserve and Site of Special Scientific Interest (SSSI) with a large bird population and plants including wild peonies. There was a signal station or watchtower on the island in Roman times, but there may have been human habitation as early as the Iron Age. In the 6th century it was home to St Gildas and to a small Augustinian priory in the 12th and 13th centuries. An inn was built in 1832 and used for holidays in the 19th century. A bird sanctuary was established in 1931 and since 1951 has been leased to charitable trusts. It is now owned by the Kenneth Allsop Memorial Trust.

In the 1860s the island was fortified with ten 7-inch rifled muzzle loaders as one of the Palmerston Forts for the coastal defence of the Bristol Channel until it was abandoned in 1898. The infrastructure was reused in World War I and II when Mark VII 6-inch breech-loading guns and search lights were installed. To enable the movement of materials, soldiers from the Indian Army Service Corps initially used mules and then installed a cable-operated winched switchback railway.

Tidal resonance

In oceanography, a tidal resonance occurs when the tide excites one of the resonant modes of the ocean.

The effect is most striking when a continental shelf is about a quarter wavelength wide. Then an incident tidal wave can be reinforced by reflections between the coast and the shelf edge, the result producing a much higher tidal range at the coast.

Famous examples of this effect are found in the Bay of Fundy, where the world's highest tides are reportedly found, and in the Bristol Channel. Less well known is Leaf Bay, part of Ungava Bay near the entrance of Hudson Strait (Canada), which has tides similar to those of the Bay of Fundy. Other resonant regions with large tides include the Patagonian Shelf and on the continental shelf of northwest Australia.Most of the resonant regions are also responsible for large fractions of the total amount of tidal energy dissipated in the oceans. Satellite altimeter data shows that the M2 tide dissipates approximately 2.5 TW, of which 261 GW is lost in the Hudson Bay complex, 208 GW on the European Shelves (including the Bristol Channel), 158 GW on the North-west Australian Shelf, 149 GW in the Yellow Sea and 112 GW on the Patagonian Shelf.

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