Tidal bore
, Alaska
A tidal bore\' (or just bore') is a tidal phenomenon in which the leading edge of the incoming tide forms a wave (or waves) of water that travel up a river against the direction of the current. As such, it is a true tidal wave (not to be confused with a tsunami). Bores occur in a relatively few locations worldwide, in areas with a large tidal range, only on certain tides, and when an incoming tide is funnelled into a shallow, narrowing river via a broad bay. A bore is a natural example of a self-reinforcing solitary wave or soliton. Larger bores can be particularly dangerous for shipping, but also present a challenge to surfers. The word bore derives through Old English from the Old Norse word bara, meaning a wave or swell. Rivers that have been known to exhibit bores include:
Brahmaputra, BangladeshIndus River, PakistanQiantang River, China, which has the world's largest bore, up to 9 metres (30 feet) high, travelling at up to 40 km per hour (25 miles an hour).
Amazon River, up to 4m (12 feet) high, running at up to 25 km per hour (15 miles per hour). It is known locally as the pororoca.
Petitcodiac River in the Bay of Fundy, New Brunswick, Canada, the highest bore in North America, up to 7.5 metres (25 feet) high.Shubenacadie River, also off the Bay of Fundy, Nova Scotia.Turnagain arm of Cook Inlet, Alaska. Up to 2 metres (6 feet) and 20 km per hour.
River Dee, Wales / EnglandRiver Mersey, EnglandRiver Severn, Wales / England up to 2 metres (7 feet) highRiver Trent, England and other tributaries of the Humber EstuaryRiver Parrett, EnglandRiver Kent, EnglandRiver Great Ouse, EnglandRiver Eden, EnglandRiver Esk, Scotland
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