Tidal bore
A tidal bore is a tidal
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the moon and the sun and the rotation of the Earth....

 phenomenon in which the leading edge of the incoming tide forms a wave (or waves) of water that travel up a river or narrow bay against the direction of the river or bay's current. As such, it is a true tidal wave and not to be confused with a tsunami
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...

, which is a large ocean wave traveling primarily on the open ocean.

The phenomenon

Bores occur in relatively few locations worldwide, usually in areas with a large tidal range (typically more than 6 metres (19.7 ft) between high and low water) and where incoming tides are funneled into a shallow, narrowing river or lake via a broad bay. The funnel-like shape not only increases the tidal range, but it can also decrease the duration of the flood tide, down to a point where the flood appears as a sudden increase in the water level. Note the tidal bore takes place during the flood tide and never during the ebb tide
Ebb Tide
"Ebb Tide" is a popular song, written in 1953 by the lyricist Carl Sigman and composer Robert Maxwell.-Recordings:* The best-known versions are by Frank Chacksfield & His Orchestra , Vic Damone , Roy Hamilton , Frank Sinatra , The Platters , Lenny Welch and the Righteous Brothers...


A tidal bore may take on various forms, ranging from a single breaking wavefront with a roller — somewhat like a hydraulic jump
Hydraulic jump
A hydraulic jump is a phenomenon in the science of hydraulics which is frequently observed in open channel flow such as rivers and spillways. When liquid at high velocity discharges into a zone of lower velocity, a rather abrupt rise occurs in the liquid surface...

 — to "undular bores", comprising a smooth wavefront followed by a train of secondary waves
The WAVES were a World War II-era division of the U.S. Navy that consisted entirely of women. The name of this group is an acronym for "Women Accepted for Volunteer Emergency Service" ; the word "emergency" implied that the acceptance of women was due to the unusual circumstances of the war and...

 ("whelps"). Large bores can be particularly unsafe for shipping but also present opportunities for river surfing
River surfing
River surfing is the sport of surfing either standing waves or tidal bores in rivers. Claims for its origins include a 1955 ride of 1.5 miles along the tidal bore of the River Severn...


Two key features of a tidal bore are the intense turbulence and turbulent mixing generated during the bore propagation, as well as its rumbling noise. The visual observations of tidal bores highlight the turbulent nature of the surging waters. The tidal bore induces a strong turbulent mixing in the estuarine zone, and the effects may be felt along considerable distances. The velocity observations indicate a rapid deceleration of the flow associated with the passage of the bore as well as large velocity fluctuations. A tidal bore creates a powerful roar that combines the sounds caused by the turbulence in the bore front and whelps, entrained air bubbles in the bore roller, sediment erosion beneath the bore front and of the banks, scouring of shoals and bars, and impacts on obstacles. The bore rumble is heard far away because its low frequencies can travel over long distances. The low-frequency sound is a characteristic feature of the advancing roller in which the air bubbles entrapped in the large-scale eddies are acoustically active and play the dominant role in the rumble-sound generation.

The word bore derives through Old English
Old English language
Old English or Anglo-Saxon is an early form of the English language that was spoken and written by the Anglo-Saxons and their descendants in parts of what are now England and southeastern Scotland between at least the mid-5th century and the mid-12th century...

 from the Old Norse word bára, meaning "wave" or "swell".


  • Ganges–Brahmaputra, India
    India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

     and Bangladesh
    Bangladesh , officially the People's Republic of Bangladesh is a sovereign state located in South Asia. It is bordered by India on all sides except for a small border with Burma to the far southeast and by the Bay of Bengal to the south...

  • Indus River
    Indus River
    The Indus River is a major river which flows through Pakistan. It also has courses through China and India.Originating in the Tibetan plateau of western China in the vicinity of Lake Mansarovar in Tibet Autonomous Region, the river runs a course through the Ladakh district of Jammu and Kashmir and...

    , Pakistan
    Pakistan , officially the Islamic Republic of Pakistan is a sovereign state in South Asia. It has a coastline along the Arabian Sea and the Gulf of Oman in the south and is bordered by Afghanistan and Iran in the west, India in the east and China in the far northeast. In the north, Tajikistan...

  • Qiantang River
    Qiantang River
    The Qiantang River is a southeast Chinese river that originates in the borders of Anhui and Jiangxi provinces and passes through Hangzhou, the capital of Zhejiang province, before flowing into the East China Sea through Hangzhou Bay....

    , China
    Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

    , which has the world's largest bore, up to 9 metres (29.5 ft) high, traveling at up to 40 kilometres (24.9 mi) per hour
  • Batang Lupar or Lupar River, near Sri Aman
    Sri Aman
    Sri Aman is a market town and port, and the capital of Sri Aman District and Sri Aman Division in Sarawak, east Malaysia.Sri Aman is also called Bandar Sri Aman, and was formerly known as Simanggang. Sri Aman in the Malay language means "town of peace ." Located on the Lupar River, it is...

    , Malaysia. The tidal bore is locally known as benak.
  • Bono, Kampar River
    Kampar River
    Kampar River is a river in northern Sumatra, Indonesia.Tributaries include the Kampar Kanan River....

    , Indonesia
    Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...

    . The phenomenon is feared by the locals to sink ships. It is reported to break up to 130 kilometres (80.8 mi) inland.


  • Styx River
    Styx River (Queensland)
    The Styx River is a short river in Queensland. It enters the Broad Sound south of the Port of St Lawrence. The river is crossed by both the Bruce Highway and North Coast railway line....

    , Queensland
    Queensland is a state of Australia, occupying the north-eastern section of the mainland continent. It is bordered by the Northern Territory, South Australia and New South Wales to the west, south-west and south respectively. To the east, Queensland is bordered by the Coral Sea and Pacific Ocean...

  • Daly River
    Daly River, Northern Territory
    Daly River is the name of a river and a town in the Northern Territory of Australia. At the 2006 census, Daly River had a population of 468.- History :...

    , Northern Territory
    Northern Territory
    The Northern Territory is a federal territory of Australia, occupying much of the centre of the mainland continent, as well as the central northern regions...

United Kingdom

  • River Dee
    River Dee, Wales
    The River Dee is a long river in the United Kingdom. It travels through Wales and England and also forms part of the border between the two countries....

    , Wales
    Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

     and England
    England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

  • River Mersey
    River Mersey
    The River Mersey is a river in North West England. It is around long, stretching from Stockport, Greater Manchester, and ending at Liverpool Bay, Merseyside. For centuries, it formed part of the ancient county divide between Lancashire and Cheshire....

  • The Severn bore
    Severn bore
    The Severn bore is a tidal bore seen on the tidal reaches of the River Severn in England. It forms somewhat upstream of Sharpness, and can be seen as far upstream as Maisemore.- Formation :...

     on the River Severn
    River Severn
    The River Severn is the longest river in Great Britain, at about , but the second longest on the British Isles, behind the River Shannon. It rises at an altitude of on Plynlimon, Ceredigion near Llanidloes, Powys, in the Cambrian Mountains of mid Wales...

    , Wales and England, up to 2 metres (6.6 ft) high
  • The Trent Aegir
    Trent Aegir
    The Trent Aegir is a tidal bore on the River Trent in England. At certain times of the year, the lower tidal reaches of the Trent experience a moderately large bore . It takes its name from Ægir, the Norse god of the ocean....

     on the River Trent
    River Trent
    The River Trent is one of the major rivers of England. Its source is in Staffordshire on the southern edge of Biddulph Moor. It flows through the Midlands until it joins the River Ouse at Trent Falls to form the Humber Estuary, which empties into the North Sea below Hull and Immingham.The Trent...

    , England, up to 1.5 metres (4.9 ft) high. Also other tributaries of the Humber Estuary
    The Humber is a large tidal estuary on the east coast of Northern England. It is formed at Trent Falls, Faxfleet, by the confluence of the tidal River Ouse and the tidal River Trent. From here to the North Sea, it forms part of the boundary between the East Riding of Yorkshire on the north bank...

  • River Parrett
    River Parrett
    The River Parrett flows through the counties of Dorset and Somerset in South West England, from its source in the Thorney Mills springs in the hills around Chedington in Dorset...

  • River Welland
    River Welland
    The River Welland is a river in the east of England, some long. It rises in the Hothorpe Hills, at Sibbertoft in Northamptonshire, then flows generally northeast to Market Harborough, Stamford and Spalding, to reach The Wash near Fosdyke. For much of its length it forms the county boundary between...

  • The Arnside Bore
    Arnside Bore
    The Arnside Bore is a tidal bore on the estuary of the River Kent in England.The bore occurs at high spring tides in Morecambe Bay opposite the village of Arnside....

     on the River Kent
    River Kent
    The River Kent is a short river in the county of Cumbria in England. The river originates in hills surrounding Kentmere, and flows for around 20 miles into the north of Morecambe Bay. The Lake District National Park includes the upper reaches of the river within its boundaries.The river passes...

  • River Great Ouse
    River Great Ouse
    The Great Ouse is a river in the east of England. At long, it is the fourth-longest river in the United Kingdom. The river has been important for navigation, and for draining the low-lying region through which it flows. Its course has been modified several times, with the first recorded being in...

  • River Ouse, Yorkshire
    River Ouse, Yorkshire
    The River Ouse is a river in North Yorkshire, England. The river is formed from the River Ure at Cuddy Shaw Reach near Linton-on-Ouse, about 6 miles downstream of the confluence of the River Swale with the River Ure...

    . Like the Trent bore, this is also known as "the Aegir".
  • River Eden
    River Eden, Cumbria
    The River Eden is a river that flows through Cumbria, England on its way to the Solway Firth.-Course of river:The Eden rises in Black Fell Moss, Mallerstang, on the high ground between High Seat, Yorkshire Dales and Hugh Seat. Here it forms the boundary between the counties of Cumbria and North...

  • River Esk
  • River Nith
    River Nith
    The River Nith is a river in South West Scotland.-Source, flow and mouth:The Nith rises in the Carsphairn hills of East Ayrshire, more precisely between Prickeny Hill and Enoch Hill, 7 km East of Dalmellington...

  • River Lune
    River Lune
    The River Lune is a river in Cumbria and Lancashire, England.It is formed at Wath, in the parish of Ravenstonedale, Cumbria, at the confluence of Sandwath Beck and Weasdale Beck...

    , Lancashire
  • River Ribble
    River Ribble
    The River Ribble is a river that runs through North Yorkshire and Lancashire, in northern England. The river's drainage basin also includes parts of Greater Manchester around Wigan.-Geography:...

    , Lancashire


The phenomenon is generally named un mascaret in French. but some other local names are preferred.
  • Seine
    The Seine is a -long river and an important commercial waterway within the Paris Basin in the north of France. It rises at Saint-Seine near Dijon in northeastern France in the Langres plateau, flowing through Paris and into the English Channel at Le Havre . It is navigable by ocean-going vessels...

    , locally named la barre, had a significant bore until the 1960s. Since then, it has been practically eliminated by dredging and river training.
  • Baie du Mont Saint Michel including Couesnon
    The Couesnon River is a river running from the département of Mayenne in north-western France, forming an estuary at Mont Saint-Michel. Its final stretch forms the border between the historical duchies of Normandy and Brittany...

    , Sélune
    The Sélune is a 91 km long river in the Manche department, Normandy, France, beginning near Saint-Cyr-du-Bailleul. It empties into the bay of Mont Saint-Michel near Avranches, close to the mouth of the Sée river. Other towns along the Sélune are Barenton, Saint-Hilaire-du-Harcouët and...

    , and Sée
    The Sée is an 78 km long river in the Manche department, Normandy, France, beginning near Sourdeval. It empties into the bay of Mont Saint-Michel in Avranches, close to the mouth of the Sélune river. Another town along the Sée is Brécey.-References:*http://www.geoportail.fr*...

  • Arguenon
  • Baie de la Frênaye
  • Vire
    Vire is a commune in the Calvados department in the Basse-Normandie region in northwestern France.- History :In 1123, Henri I Beauclerc, King of England and Duke of Normandy, had a redoubt constructed on a rocky hill top, which was surrounded by the Vire river...

  • Sienne
  • Vilaine
    The Vilaine is a river in Brittany, in the west of France. The river's source is in the Mayenne département , and flows out in the Atlantic Ocean at Pénestin in the Morbihan département . It is 218 km long...

    , locally named le mascarin
  • Dordogne
    Dordogne is a départment in south-west France. The départment is located in the region of Aquitaine, between the Loire valley and the High Pyrénées named after the great river Dordogne that runs through it...

  • Garonne
    The Garonne is a river in southwest France and northern Spain, with a length of .-Source:The Garonne's headwaters are to be found in the Aran Valley in the Pyrenees, though three different locations have been proposed as the true source: the Uelh deth Garona at Plan de Beret , the Ratera-Saboredo...

United States

  • The Turnagain arm of Cook Inlet
    Cook Inlet
    Cook Inlet stretches from the Gulf of Alaska to Anchorage in south-central Alaska. Cook Inlet branches into the Knik Arm and Turnagain Arm at its northern end, almost surrounding Anchorage....

    , Alaska. Up to 2 metres (6.6 ft) and 20 km/h.


Most rivers draining into the upper Bay of Fundy
Bay of Fundy
The Bay of Fundy is a bay on the Atlantic coast of North America, on the northeast end of the Gulf of Maine between the Canadian provinces of New Brunswick and Nova Scotia, with a small portion touching the U.S. state of Maine...

 between Nova Scotia
Nova Scotia
Nova Scotia is one of Canada's three Maritime provinces and is the most populous province in Atlantic Canada. The name of the province is Latin for "New Scotland," but "Nova Scotia" is the recognized, English-language name of the province. The provincial capital is Halifax. Nova Scotia is the...

 and New Brunswick
New Brunswick
New Brunswick is one of Canada's three Maritime provinces and is the only province in the federation that is constitutionally bilingual . The provincial capital is Fredericton and Saint John is the most populous city. Greater Moncton is the largest Census Metropolitan Area...

 have tidal bores. Notable ones include:
  • The Petitcodiac River
    Petitcodiac River
    The Petitcodiac River is a Canadian river in south-eastern New Brunswick. The river runs about through the province's Westmorland, Albert, and Kings counties, draining a watershed area of about . The region around the river features valleys, ridges, and rolling hills, and is home to a diverse...

    . Formerly the highest bore in North America at over 2 metres (6.6 ft); however, causeway
    In modern usage, a causeway is a road or railway elevated, usually across a broad body of water or wetland.- Etymology :When first used, the word appeared in a form such as “causey way” making clear its derivation from the earlier form “causey”. This word seems to have come from the same source by...

     construction and extensive silt
    Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...

    ing reduced it to little more than a ripple, until the causeway gates were opened on April 14, 2010, as part of the Petitcodiac River Restoration project and the tidal bore began to grow again.
  • The Shubenacadie River
    Shubenacadie River
    The Shubenacadie River is a river in Nova Scotia, Canada.It has a meander length of approximately 72 km from its source at Shubenacadie Grand Lake to its mouth at the historic seaport village of Maitland on Cobequid Bay, site of the building of the William D. Lawrence, the largest wooden ship ever...

    , also off the Bay of Fundy in Nova Scotia. When the tidal bore approaches, completely drained riverbeds are filled. It has claimed the lives of several tourists who were in the riverbeds when the bore came in. Tour boat operators offer rafting excursions in the summer.
  • The bore is fastest and highest on some of the smaller rivers that connect to the bay including the River Hebert
    River Hebert
    The River Hebert is a small tidal river that empties into the Cumberland Basin, contained completely within Cumberland County, Nova Scotia....

     and Maccan River
    Maccan River
    The Maccan River is a small tidal river contained completely within Cumberland County, Nova Scotia. The river terminates at the confluence with River Hebert at Amherst Point, and empties into the Cumberland Basin. The river's tidal bore may be viewed from the Tidal Wetlands Park in...

     on the Cumberland Basin, the St. Croix
    St. Croix River (Nova Scotia)
    The St. Croix River is a river in Nova Scotia entirely contained in Hants and Halifax Counties. Its headwaters are Panuke Lake. The river has been exploited for water power. There were water mills in the nineteenth century and in the 1930’s three hydroelectric dams were built; they still...

    , Herbert and Kennetcook
    Kennetcook River
    The Kennetcook River is a river that flows through Hants County, Nova Scotia. From headwaters near the mouth of the Shubenacadie River, the Kennetcook traverses about 45 kilometres of mostly rural terrain, discharging into the Avon River at Windsor. The Kennetcook cuts through fossiliferous...

     Rivers in the Minas Basin
    Minas Basin
    The Minas Basin is an inlet of the Bay of Fundy and a sub-basin of the Fundy Basin located in Nova Scotia, Canada. It is known for its extremely high tides.- Geography :- Boundary :...

    , and the Salmon River
    Salmon River (Nova Scotia)
    The Salmon River is a Canadian river in central Nova Scotia's Colchester County.Rising in the Cobequid Hills in the central-northeastern part of the county, the river descends through a broad glacial valley at the head of Cobequid Bay, the eastern extremity of the Bay of Fundy...

     in Truro.


There is a tidal bore on the Sea of Cortez in Mexico at the entrance of the Colorado River
Colorado River
The Colorado River , is a river in the Southwestern United States and northwestern Mexico, approximately long, draining a part of the arid regions on the western slope of the Rocky Mountains. The watershed of the Colorado River covers in parts of seven U.S. states and two Mexican states...

. It forms in the estuary about Montague Island
Montague Island (Mexico)
Montague Island, known in Spanish as Isla Montague, is an island at the mouth of the Colorado River in the municipality of Mexicali, Baja California, Mexico, and is part of the Colorado River Delta and part of a broader region called the Salton Trough...

 and propagates upstream. Once very strong, later diversions of the river for irrigation have weakened the flow of the river to the point the tidal bore has nearly disappeared.

South America

  • Amazon River
    Amazon River
    The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...

     in Brazil
    Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

     and Orinoco River in Venezuela
    Venezuela , officially called the Bolivarian Republic of Venezuela , is a tropical country on the northern coast of South America. It borders Colombia to the west, Guyana to the east, and Brazil to the south...

    , up to 4 metres (13.1 ft) high, running at up to 13 miles per hour (5.8 m/s). It is known locally as the pororoca
    The pororoca is a tidal bore, with waves up to 4 metres high that travel as much as 13 km inland upstream on the Amazon River and adjacent rivers. Its name comes from the indigenous Tupi language, where it translates into "great destructive noise". It occurs at the mouth of the river where river...

  • Mearim River
    Mearim River
    The Mearim River is a river in Maranhão state of northern Brazil. The river originates in the southern part of Maranhão, and drains north into the Baía de São Marcos, an estuary that also receives the Pindaré and Grajaú rivers, which are sometimes considered tributaries of the Mearim. The lower...

     in Brazil
  • Araguari River
    Araguari River (Amapá)
    Araguari River is the primary river of Amapá state in north-eastern Brazil.Araguari River is the primary river of Amapá state in north Brazil.-References:*...

     in Brazil

Lakes with tidal bores

Lakes with an ocean inlet
An inlet is a narrow body of water between islands or leading inland from a larger body of water, often leading to an enclosed body of water, such as a sound, bay, lagoon or marsh. In sea coasts an inlet usually refers to the actual connection between a bay and the ocean and is often called an...

 can also exhibit tidal bores.

North America

  • Nitinat Lake
    Nitinat Lake
    Nitinat Lake is a large lake and inlet on the southwestern coast of Vancouver Island, British Columbia, Canada. The lake is about northwest by road from Victoria, BC's capital on the southern tip of Vancouver Island, and about southeast by road from the town of Lake Cowichan...

     on Vancouver Island
    Vancouver Island
    Vancouver Island is a large island in British Columbia, Canada. It is one of several North American locations named after George Vancouver, the British Royal Navy officer who explored the Pacific Northwest coast of North America between 1791 and 1794...

     has a sometimes dangerous tidal bore at Nitinat Narrows where the lake meets the Pacific Ocean. The lake is popular with windsurfers due to its consistent winds.

Impact of tidal bores

The tidal bores may be dangerous and some bores have had a sinister reputation. For example, the tidal bores of the Seine River (France), of the Petitcodiac River (Canada) and of the Colorado River (Mexico). In China, despite warning signs erected along the Qiantang River banks, a number of tragic accidents happen each year. The tidal bores affect the shipping and navigation in the estuarine zone, for example in Papua New Guinea
Papua New Guinea
Papua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...

 (Fly and Bamu Rivers), Malaysia (Benak at Batang Lupar), and India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

 (Hoogly bore).

On the other hand, the tidal-bore affected estuaries are the rich feeding zones and breeding grounds of several forms of wildlife. The estuarine zones are the spawning and breeding grounds of several native fish species, while the aeration induced by the tidal bore contribute to the abundant growth of many species of fish and shrimps (for example in the Rokan River).

Scientific studies of tidal bores

Scientific measurements in tidal bores are challenging because of the force of the tidal bore flow. This is evidenced by a number of field work incidents in the Dee River, Rio Mearim, Daly River and Sélune River: "during this […] deployment, the [ADCP] instrument was repeatedly buried in sediment after the 1st tidal cycle and had to be dug out of the sediment, with considerable difficulty, at the time of recovery" (Dee River); "About 20 min after the passage of the bore the two aluminium frames at site C were toppled. […] A 3-min-duration patch of macroturbulence was observed. […] This unsteady motion was sufficiently energetic to topple moorings that had survived much higher, quasi-steady currents of 1.8 m/s" (Daly River); "the field study experienced a number of problems and failures. About 40 s after the passage of the bore, the metallic frame started to move. The ADV support failed completely 10 minutes after the tidal bore." (Sélune River).

See also

  • 1812 New Madrid earthquake, a historic earthquake in the United States that caused the Mississippi River to flow backwards temporarily
  • Hydraulic jump
    Hydraulic jump
    A hydraulic jump is a phenomenon in the science of hydraulics which is frequently observed in open channel flow such as rivers and spillways. When liquid at high velocity discharges into a zone of lower velocity, a rather abrupt rise occurs in the liquid surface...

  • Tidal race
    Tidal race
    Tidal race is a natural occurrence whereby a fast moving tide passes through a constriction resulting in the formation of waves, eddies and hazardous currents...

  • Tonlé Sap
    Tonlé Sap
    The Tonlé Sap is a combined lake and river system of major importance to Cambodia.The Tonlé Sap is the largest freshwater lake in South East Asia and is an ecological hot spot that was designated as a UNESCO biosphere in 1997....

    , a lake and river system in Cambodia where monsoon flooding can cause the river to flow backwards temporarily
  • Undular bore wave

External links

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