Tidal race
Encyclopedia
Tidal race is a natural occurrence whereby a fast moving tide
passes through a constriction resulting in the formation of wave
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
or rising seabed
), such as is found at the Portland Race
.
In extreme cases, such as Skookumchuck Narrows
in British Columbia
, through which tides can travel at more than 17 knots, very large whirlpool
s develop, which can be extremely hazardous to navigation.
Tide
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....
passes through a constriction resulting in the formation of wave
Wave
In physics, a wave is a disturbance that travels through space and time, accompanied by the transfer of energy.Waves travel and the wave motion transfers energy from one point to another, often with no permanent displacement of the particles of the medium—that is, with little or no associated mass...
s, eddies
Eddy (fluid dynamics)
In fluid dynamics, an eddy is the swirling of a fluid and the reverse current created when the fluid flows past an obstacle. The moving fluid creates a space devoid of downstream-flowing fluid on the downstream side of the object...
and hazardous currents
Ocean current
An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as breaking waves, wind, Coriolis effect, cabbeling, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun...
. The constriction can be a passage where the sides narrow, for example the Gulf of Corryvreckan
Gulf of Corryvreckan
The Gulf of Corryvreckan , also called the Strait of Corryvreckan, is a narrow strait between the islands of Jura and Scarba, in Argyll and Bute, off the west coast of Scotland.It is possible for tourists to visit the site by way of boats trips from local harbours.- Topography...
and the Saltstraumen
Saltstraumen
Saltstraumen is a sound with a strong tidal current located in Nordland 30 km east of the city of Bodø, Norway. The narrow channel connects the outer Saltfjord with its extension, the large Skjerstadfjord. It is the strongest tidal current in the world...
maelstrom
Maelstrom
A maelstrom is a very powerful whirlpool; a large, swirling body of water. A free vortex, it has considerable downdraft. The power of tidal whirlpools tends to be exaggerated by laymen. There are virtually no stories of large ships ever being sucked into a maelstrom, although smaller craft are in...
, or an underwater obstruction (a reef
Reef
In nautical terminology, a reef is a rock, sandbar, or other feature lying beneath the surface of the water ....
or rising seabed
Seabed
The seabed is the bottom of the ocean.- Ocean structure :Most of the oceans have a common structure, created by common physical phenomena, mainly from tectonic movement, and sediment from various sources...
), such as is found at the Portland Race
Isle of Portland
The Isle of Portland is a limestone tied island, long by wide, in the English Channel. Portland is south of the resort of Weymouth, forming the southernmost point of the county of Dorset, England. A tombolo over which runs the A354 road connects it to Chesil Beach and the mainland. Portland and...
.
In extreme cases, such as Skookumchuck Narrows
Skookumchuck Narrows
Skookumchuck Narrows forms 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 pass through Sechelt Rapids. At peak flows, whitecaps and whirlpools form at...
in British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
, through which tides can travel at more than 17 knots, very large whirlpool
Whirlpool
A whirlpool is a swirling body of water usually produced by ocean tides. The vast majority of whirlpools are not very powerful. More powerful ones are more properly termed maelstroms. Vortex is the proper term for any whirlpool that has a downdraft...
s develop, which can be extremely hazardous to navigation.
Notable tidal races
- Cape ReingaCape ReingaCape Reinga is the northwesternmost tip of the Aupouri Peninsula, at the northern end of the North Island of New Zealand. Cape Reinga is located over 100 km north of the nearest small town of Kaitaia. State Highway 1 extends all the way to the Cape, but until 2010 was unsealed gravel road for the...
in New ZealandNew ZealandNew Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga... - Skookumchuck NarrowsSkookumchuck NarrowsSkookumchuck Narrows forms 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 pass through Sechelt Rapids. At peak flows, whitecaps and whirlpools form at...
in British ColumbiaBritish ColumbiaBritish Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
, CanadaCanadaCanada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean... - The BitchesThe BitchesThe Bitches are a tidal race and set of rocks between Ramsey Island and the west Welsh coastline near St. Davids. It is a popular tourist destination and playspot for extreme sports enthusiasts such as whitewater kayakers and surfers.-Formation:...
in WalesWalesWales 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...
, United KingdomUnited KingdomThe United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages... - Falls of LoraFalls of LoraThe 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....
in ScotlandScotlandScotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...
, United Kingdom - Portland BillPortland BillPortland Bill is a narrow promontory of Portland stone, which forms the most southerly part of Isle of Portland, and therefore also the county of Dorset, England....
on the Isle of PortlandIsle of PortlandThe Isle of Portland is a limestone tied island, long by wide, in the English Channel. Portland is south of the resort of Weymouth, forming the southernmost point of the county of Dorset, England. A tombolo over which runs the A354 road connects it to Chesil Beach and the mainland. Portland and...
, United Kingdom - The Alderney Race (12 knots+) on AlderneyAlderneyAlderney is the most northerly of the Channel Islands. It is part of the Bailiwick of Guernsey, a British Crown dependency. It is long and wide. The area is , making it the third-largest island of the Channel Islands, and the second largest in the Bailiwick...
, United Kingdom - Horizontal FallsHorizontal FallsThe Horizontal Falls, also called Horizontal Waterfalls are a natural phenomenon in the Kimberley region of Western Australia, in Australia....
in Western AustraliaWestern AustraliaWestern Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
, AustraliaAustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
See also
- Rip currentRip currentA rip current, commonly referred to by the misnomer rip tide, is a strong channel of water flowing seaward from near the shore, typically through the surf line. Typical flow is at 0.5 metres per second , and can be as fast as 2.5 metres per second...
- Tidal boreTidal boreA tidal bore is a tidal phenomenon in which the leading edge of the incoming tide forms a wave of water that travel up a river or narrow bay against the direction of the river or bay's current...