Tidal race

View to Lunga from Scarba, across the 'Grey Dog' tidal race.

Tidal race (or tidal rapid) is a natural occurrence whereby a fast moving tide passes through a constriction resulting in the formation of waves, 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 whirlpools develop, which can be extremely hazardous to navigation.

Notable tidal races

• Cape Reinga in New Zealand
• Skookumchuck Narrows in British Columbia, Canada
• The Bitches in Wales, United Kingdom
• Falls of Lora in Scotland, United Kingdom
• Portland Bill on the Isle of Portland, United Kingdom
• The Alderney Race (12 knots+) on Alderney.
• Horizontal Falls in Western Australia, Australia

See also

• Rip current
• Tidal bore