Tidal race or tidal rapid is a natural occurrence whereby a fast-moving

tide Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables can ...

passes through a constriction, resulting in the formation of

wave In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (r ...

s, eddies and hazardous currents. The constriction can be a passage where the sides narrow, for example the Gulf of Corryvreckan and the Saltstraumen maelstrom, or an underwater obstruction (a

reef A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic component, abiotic processes—deposition (geology), deposition of ...

or rising

seabed The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as 'seabeds'. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...

), such as is found at the Portland Race in the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

. In extreme cases, such as Skookumchuck Narrows in

British Columbia British Columbia (commonly abbreviated as BC) is the westernmost Provinces and territories of Canada, province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include ...

, through which tides can travel at more than 17 knots, very large

whirlpool A whirlpool is a body of rotating water produced by opposing currents or a current running into an obstacle. Small whirlpools form when a bath or a sink is draining. More powerful ones formed in seas or oceans may be called maelstroms ( ). ''Vo ...

s develop, which can be extremely hazardous to navigation.

Notable tidal races

Cape Reinga , type =Cape , photo = Cape Reinga, Northland, New Zealand, October 2007.jpg , photo_width = 270px , photo_alt = , photo_caption = , map = New Zealand , map_width = 270px ...

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 List of islands of New Zealand, smaller islands. It is the ...

* Skookumchuck Narrows in

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tota ...

* The Bitches in

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 ...

Bitches and Tides
* Falls of Lora in

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to th ...

, United Kingdom *

Portland Bill Portland Bill is a narrow promontory (or bill) at the southern end of the Isle of Portland, and the southernmost point of Dorset, England. One of Portland's most popular destinations is Portland Bill Lighthouse. Portland's coast has been notorio ...

on the

Isle of Portland An isle is an island, land surrounded by water. The term is very common in British English. However, there is no clear agreement on what makes an island an isle or its difference, so they are considered synonyms. Isle may refer to: Geography * ...

, United Kingdom * The

Alderney Race The Alderney Race is a strait that runs between Alderney and Cap de la Hague, a cape at the northwestern tip of the Cotentin Peninsula in Normandy. A strong current runs through the race north of the Passage de la Déroute, a treacherous passage s ...

(12 knots+) on

Alderney Alderney (; french: Aurigny ; Auregnais: ) is the northernmost of the inhabited Channel Islands. It is part of the Bailiwick of Guernsey, a British Crown dependency. It is long and wide. The island's area is , making it the third-larges ...

* Horizontal Falls in

Western Australia Western Australia (commonly abbreviated as WA) is a state of Australia occupying the western percent of the land area of Australia excluding external territories. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to ...

, Australia * Naruto Strait between

Shikoku is the smallest of the four main islands of Japan. It is long and between wide. It has a population of 3.8 million (, 3.1%). It is south of Honshu and northeast of Kyushu. Shikoku's ancient names include ''Iyo-no-futana-shima'' (), ...

and Awaji Islands, Japan *

Reversing Falls The Reversing Falls are a series of rapids on the Saint John River located in Saint John, New Brunswick, Canada, where the river runs through a narrow gorge before emptying into the Bay of Fundy. The semidiurnal tides of the bay force the flo ...

Saint John, New Brunswick Saint John is a seaport city of the Atlantic Ocean located on the Bay of Fundy in the province of New Brunswick, Canada. Saint John is the oldest incorporated city in Canada, established by royal charter on May 18, 1785, during the reign of K ...

, Canada

Sources

{{DEFAULTSORT:Tidal Race Tides Whirlpools

Notable tidal races

See also

Sources