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 gravity, 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 t ...

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 (res ...

eddies In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid is in a turbulent flow regime. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the object. Fluid beh ...

and hazardous

currents Currents, Current or The Current may refer to: Science and technology * Current (fluid), the flow of a liquid or a gas ** Air current, a flow of air ** Ocean current, a current in the ocean *** Rip current, a kind of water current ** Current (stre ...

. The constriction can be a passage where the sides narrow, for example the

Gulf of Corryvreckan The Gulf of Corryvreckan (from the Gaelic ''Coire Bhreacain'', meaning 'cauldron of the speckled seas' or 'cauldron of the plaid'), also called the Strait of Corryvreckan, is a narrow strait between the islands of Jura and Scarba, in Argyll and ...

and the

Saltstraumen Saltstraumen is a small strait with one of the strongest tidal currents in the world. It is located in the municipality of Bodø in Nordland county, Norway. It is located about southeast of the town of Bodø. The narrow channel connects the out ...

maelstrom Maelstrom may refer to: * Maelstrom (whirlpool), a powerful whirlpool ** originally the Moskstraumen in English Amusement rides * Maelstrom (ride), a former log flume dark ride attraction in the Epcot theme park at Walt Disney World Resort ...

, 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 processes— deposition of sand, wave erosion planing down rock out ...

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 continental mainland. It comprises England, Scotland, Wales and North ...

. In extreme cases, such as

Skookumchuck Narrows Skookumchuck Narrows is a strait forming the entrance of Sechelt Inlet on British Columbia's Sunshine Coast in Canada. Before broadening into Sechelt Inlet, all of its tidal flow together with that of Salmon Inlet and Narrows Inlet must pa ...

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

, through which tides can travel at more than 17

knots A knot is a fastening in rope or interwoven lines. Knot may also refer to: Places * Knot, Nancowry, a village in India Archaeology * Knot of Isis (tyet), symbol of welfare/life. * Minoan snake goddess figurines#Sacral knot Arts, entertainme ...

, 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 smaller islands. It is the sixth-largest island count ...

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 tot ...

The Bitches The Bitches (also known as Bitches and Whelps) are a tidal race and set of rocks between Ramsey Island and the west Welsh coastline near St Davids. They are a popular tourist destination and a playspot for extreme waterboarding enthusiasts su ...

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 The Falls of Lora is a tidal race which forms at the mouth of Loch Etive when a particularly high tide runs out from the loch. They form white water rapids for two to five days either side of the spring tides.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 the ...

, 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 * Is ...

, 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-largest ...

Horizontal Falls The Horizontal Falls, or Horizontal Waterfalls, nicknamed the "Horries" and known as Garaanngaddim by the local Indigenous people, are an unusual natural phenomenon on the coast of the Kimberley region in Western Australia, where tidal flows ...

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 th ...

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Naruto Strait is a strait between Awaji Island and Shikoku in Japan. It connects Harima Nada, the eastern part of the Inland Sea and the Kii Channel. A famous feature of the strait is the Naruto whirlpools. Ōnaruto Bridge, the southern part of the Kobe-A ...

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 Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

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 flow ...

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 Ki ...

, Canada

Sources

{{DEFAULTSORT:Tidal Race Tides Whirlpools

Notable tidal races

See also

Sources